Abstract

We report on the observation of uranium monoxide (UO) emission following fs laser ablation (LA) of a uranium metal sample. The formation and evolution of the molecular emission is studied under various ambient air pressures. Observation of UO emission spectra at a rarefied residual air pressure of ~1 Torr indicates that the UO molecule is readily formed in the expanding plasma with trace concentrations of oxygen present within the vacuum chamber. The persistence of the UO emission exceeded that of the atomic emission; however, the molecular emission was delayed in time compared to the atomic emission due to the necessary cooling and expansion of the plasma before the UO molecules can form.

© 2017 Optical Society of America

1. Introduction

Laser ablation (LA) is a powerful technique that has been implemented in a number of material processing and analytical applications. Some of the well-known material processing applications include micro-fabrication/machining, additive manufacturing, and thin-film deposition [1]. Similarly, LA is an integral component of common analytical techniques like laser ablation inductively coupled mass spectroscopy (LA-ICP-MS), laser ablation laser absorption spectroscopy (LA-LAS), and laser-induced breakdown spectroscopy (LIBS) [2–4]. LA is a simple technique that requires a limited number of optical components – a pulsed high-power laser and a focusing lens. However, while the application of LA may be simple, the LA process is largely unexplored at the fundamental level since the underlying physics is exceptionally complex. The properties of the laser-induced plasma that results from LA depend on the laser parameters such as focal spot size, wavelength, pulse duration, and intensity [2]. It has been widely reported that LA with short-pulse lasers (e.g., ps and fs pulse durations) exhibits reduced laser-plasma coupling (inverse bremsstrahlung), a smaller heat affected zone, and a reduced magnitude of bremsstrahlung emission compared to LA with long (ns) laser pulses [5]. Further, it has been reported in the literature that ablation with shorter wavelength laser pulses exhibits a lower ablation threshold and reduced elemental fractionation compared to longer wavelength laser pulses [6]. Within the available literature, a number of studies have considered the effect of laser pulse duration, wavelength, and intensity on LA and the resulting laser-induced plasma at a fundamental level [7].

LIBS is a powerful all-optical technique for direct and rapid elemental analysis [2]. The technique involves the collection and spectral analysis of the emitted light from the luminous plasma produced following LA on the surface of a sample. One benefit of the LIBS technique is its inherent compatibility with standoff measurements due to its all-optical nature [8, 9]. LIBS can be used not only for elemental analysis, but isotopic analysis as well, and has been applied to measure several isotopes of B, Li, Zr, Pu, and U, for example [10–14].

The formation and emission of molecular species within laser-induced plasmas has been the subject of a number of recent studies [15–20]. The increased interest in molecular emissions has been largely driven by the notion that their measurement may provide more robust isotopic identification and discrimination [12, 14]. Vibronic emission spectra from diatomic molecules exhibit an isotope dependence, and the isotope shifts of the molecular emission lines are often greater than the isotope shifts of atomic and ionic emission lines especially for lighter molecules [16]. Molecular emissions from BO have been studied extensively for measurement of the B isotopes in B-containing samples [12, 14, 21]. In laser-induced plasmas molecules are formed through a number of reaction pathways: combustion or oxidation by direct interaction with the ambient atmosphere, recombination between species present within the plasma, and fragmentation of larger molecular clusters [18,20,22]. The laser pulse duration significantly impacts the fundamental properties of laser ablation plumes, which in turn affects the resulting emission properties of the expanding plasma plume. The molecular emissions are observed at longer delays after the arrival of the laser pulse (>1 μs for fs LA), when the plasma has cooled and undergone significant expansion into the ambient atmosphere, and persist for longer periods compared to the excited atomic and ionic emissions [16, 18, 19, 23]. When compared to ns-LA, fs-LA exhibits a number of distinguishing characteristics, including a lower plasma temperature, rapid plasma temperature decay, increased ablation efficiency, and the presence of a primarily atomic plume, resulting in more favorable conditions for molecular formation [7]. The emission intensity, delay, and persistence of the atomic, ionic, and molecular emissions are influenced by the plasma chemistry. Within the available literature, only a few works are available that have reported on the formation and evolution of the molecules and their emission, respectively, within a laser-induced plasma [15, 20, 22, 24].

In the context of molecular emission, significant work has been reported in the available literature on molecules comprised of low-Z elements such as B, Zr, Sr, and Al [14, 18, 19, 23]. The majority of these studies have been focused on the diatomic oxides that low-Z elements form in the ambient atmosphere. Even though a number of studies are available on the emission of diatomic molecules, little is known on the formation of more complex polyatomic molecules in a laser-induced plasma. The formation of polyatomic molecules is likely for elements like U and Al, which would deplete the population of diatomic molecules. Further, the formation of molecules within the plasma is dependent on the plasma chemistry, which is influenced by the ambient atmospheric conditions, and has not been studied for high-Z elements like U. Wormhoudt et al. reported on the reaction of uranium with ambient oxygen and showed that gaseous uranium readily reacts with oxygen to form uranium oxides [25]. Kaledin et al. reported on the emission of gaseous UO that was cooled through supersonic expansion of the UO gas to temperatures of ~130 K [26]. The collection of high-resolution gas phase electronic spectra of UO enabled the determination of molecular constants for low-lying electronic states of UO. While extensive literature exists on low-Z diatomic molecular emission in laser-induced plasmas, the understanding of the characteristics of uranium molecular emissions from laser-induced plasmas is lacking at the present time.

Recent work by our group has shown that the uranium plasma is very sensitive to the composition of the ambient atmosphere; a significant reduction in persistence of a U atomic ground state transition between ambient air and N2 environments has been observed in absorption studies [15]. The abundance of reactive species such as O2 in air leads to the formation of uranium oxides that may be responsible for the quenching of the atomic absorption signal. Limited studies exist on the effect of ambient atmospheric conditions on uranium laser-induced plasma emission and chemistry [15, 17, 27], and even fewer of them consider the formation of uranium oxides within LA plasmas [15, 17]. Due to the inherent nature of standoff measurements, LA is performed under ambient atmospheric conditions, which is why the formation and chemistry of uranium oxides within the plasma formed in air and their effect on the measured emission signal must be elucidated.

In this work, we report on the formation and dynamics of uranium molecules (uranium monoxide) in a laser-induced plasma. The plasma is formed following fs LA of a solid uranium metal sample (natural isotopic composition) contained within a vacuum chamber where the pressure and composition of the ambient atmosphere is varied. Uranium atomic and molecular emission features over a range of different air pressures and emission wavelengths are studied.

2. Experimental setup

The sample used was a uranium metal foil (natural isotopic composition, 0.7% 235U), with a size of approximately 0.5 cm x 2.0 cm and was lightly oxidized with minor surface defects. The sample was provided by The Pennsylvania State University’s Radiation Science and Engineering Center.

A schematic of the experimental setup is shown in Fig. 1. The vacuum chamber was evacuated to a residual pressure of ~0.5 Torr and backfilled with argon or air through an installed tube feedthrough. The sample was mounted to a holder, which is capable of translating the sample along the x- and y-axes perpendicular to the laser beam. The fs laser was a commercial Ti:sapphire chirped-pulse amplification system (Trident X, Amplitude Technologies), from which ~6 mJ, 800 nm pulses were split at a minimum pulse duration (FWHM) of 42 fs and at 10 Hz repetition rate.

 figure: Fig. 1

Fig. 1 Simplified schematic of the experimental setup utilized in this work, which is licensed for laser ablation analysis of radioactive and special nuclear materials (SNM).

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The fs laser pulses were focused using a 30 cm focal length BK7 lens normal to the sample surface, producing a spot size of ~200 μm. The emission from the luminous plasma was collected and coupled into an optical fiber by a 5.0 cm focal length achromatic lens (400–700 nm) mounted at an angle of ~45° with respect to the laser beam path; hence the spectral emission from the plasma is spatially integrated. The optical fiber (a 1 mm diameter fiber bundle) was coupled out of the vacuum chamber through a fiber feedthrough and terminated at the spectrometer in a linear arrangement aligned to the entrance slit. The spectrometer (Horiba Jobin Yvon iHR 550) had an 1800 grooves/mm grating coupled to an Andor iStar 334t intensified CCD (ICCD). The plasma emission collection optics and spectrometer system were intensity calibrated using an Ocean Optics DH2000 Deuterium Tungsten calibration lamp.

For LIBS measurements, the plasma was generated over a range of ambient air and inert gas pressures measured using a digital manometer connected to the vacuum chamber. The ICCD acquisition gate delay and width was varied according to the measurement requirements, and each measurement was synchronized to the laser pulse using a Stanford Research Instruments (SRS DG645) Digital Delay Generator. Each spectrum is the accumulation of 10 individual laser ablation spectral measurements. Two cleaning shots were performed before each spectral measurement, which served to remove the thin oxide layer on the uranium metal sample.

3. Results

3.1 Spectral analysis of uranium plasmas

LA of uranium samples allows for the study of the atomic, ionic, and molecular species that are formed in the expanding plasma plume and through interaction of the plume with the ambient atmosphere. Depending on the irradiation conditions (pulse duration, laser wavelength, focusing configuration, etc.), the temporal behavior of the emitting atoms, ions and molecules can change drastically. Typically, LA plumes are hotter and denser at the earlier times of plasma evolution and become cooler and less dense as the plasma expands into the ambient atmosphere [28]. Due to high temperatures at early times of plasma evolution, free-free (bremsstrahlung) and free-bound (recombination) emissions dominate over bound-bound (characteristic spectral lines) emissions. Even though it is well known that ultrafast LA reduces the magnitude of continuum emission, the size of the heat affected zone, and the plasma temperature in comparison with ns LA [7] (which should create a favorable environment for molecular formation), limited experimental studies are available that provide evidence of these characteristics of fs LA of U metal.

Figure 2 shows the LIBS emission spectrum in the range of 400–600 nm from fs-LA of a uranium metal sample recorded with an ambient Ar pressure of ~82 Torr. Since U is a high-Z material, its plasma emits a very crowded emission spectrum. Many of the strongest optical transitions and energy levels for U atoms and ions have been reported in the literature [29, 30]. Selected uranium emission lines are indicated in the spectrum (Fig. 2) for both neutral (blue) and ionic (red) atomic emissions.

 figure: Fig. 2

Fig. 2 Intensity calibrated LIBS emission spectrum of natural uranium metal sample following femtosecond laser ablation in the range of (a) 400 – 500 nm and (b) 500 – 600 nm with a 1.0 μs gate delay and 10 μs gate width averaged over 10 laser shots. After the vacuum chamber was evacuated, it was filled with argon to a pressure of 82 Torr; however, 3 Torr of ambient air leaked into the chamber during the measurement. Strong and commonly referenced uranium emission lines are labeled in the spectrum for neutral (blue), ionic (red), and molecular (black) emissions.

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3.2 Identification of uranium molecular emission from fs-LIBS plasmas

The fs LIBS spectrum shown in Fig. 2 was acquired under a rarefied Ar atmosphere of 82 Torr; however, due to the use of HEPA filters and additional fittings on the vacuum chamber to satisfy the mandated experimental safety procedure, a small but constant air leak into the chamber was observed. For the case of Fig. 2, the air leak caused approximately 3 Torr partial pressure of air to be present by the end of the spectral scan. The inset of Fig. 2(b) shows the uranium fs LIBS emission spectra for the spectral range studied by Kaledin et al. [26], where the authors identified a number of uranium monoxide (UO) emissions, including a strong Q branch emission centered at 593.57 nm. From inspection of the inset in Fig. 2(b), an emission feature is observed at 593.57 nm, and a review of the Los Alamos Scientific Laboratory Uranium Atlas [30], the Kurucz Database [31], and the NIST Atomic Line Database [32] reveals that this emission feature is not associated with either U I or U II emissions. Additional emission bandheads reported by Kaledin et al. [26] were not observed in the measured spectra, which could be due to the low intensity of the molecular emissions and spectral interference from nearby U I and U II emissions.

Uranium is pyrophoric and will oxidize when heated in an ambient air atmosphere [33]. In previous work by Kaledin et al. [26], Heaven et al. [34], and Wormhoudt [25], the emission of UO from the reaction of U with O2 has been identified, 38 vibronic bands analyzed including the 235U and 18O isotopologues, and the center of one strong band for 238U16O is reported at 593.52 nm. Also, in emission at approximately 2500 K a strong band is reported at 593.48 nm. The latter study showed the dependence of the UO formation rate and emission on the concentration of O2 available for the U to oxidize with. As the O2 concentration was increased, uranium in the reaction flow tube readily formed UO2 and UO3 that reduced the population of UO. Moreover, Wormhoudt et al. showed that U oxidizes in the presence of O2 and forms UO even when only trace concentrations of O2 are present [25]. Based on these prior findings, it is hypothesized that the 593.57 nm emission line observed in Fig. 2 is due to UO emission. To confirm that this emission line is associated with a molecular transition, temporally resolved emission measurements and pressure dependent studies were performed.

3.3 Dynamics of uranium molecular emission in fs-LIBS plasmas

The ambient air pressure influences the physical and chemical conditions of the plume, which in turn affect the temporal history of the population of excited neutral atoms, ions, and molecules [8, 15, 23]. For example, the formation of UO within the plasma is dependent on the oxidation of uranium atoms in the plume in the ambient atmosphere. To further examine this dependence, we assessed the time evolution of U plasma spectral features at various ambient air pressures in the spectral region of 590–597 nm, where the UO band resides. Figure 3 shows the temporal behavior of the uranium emission spectrum as for several gate delays and widths at three different pressures (95, 440, and 730 Torr). At early times (100 ns delay), the spectrum is dominated by the bremsstrahlung and recombination emissions for all three pressures; however, several uranium atomic emissions are also visible, for example at 591.53 and 593.38 nm. At 1 μs delay the uranium atomic and molecular emissions are clearly visible for the 440 and 730 Torr pressures. As the plasma evolves (2 μs delay), the uranium molecular emission intensity increases above the nearby 593.38 U I emission. At late times (8 μs delay), the uranium molecular emission becomes isolated for the 440 and 730 Torr pressures, and only the strong 591.53 nm U I transition to the ground state is visible.

 figure: Fig. 3

Fig. 3 Uranium LIBS spectra at 95, 440, and 730 Torr air pressure for several gate delays and widths. The spectra were intensity corrected for a range of ICCD gains used during the measurement. A vertical dashed line has been placed at the center of the observed UO emission line to help guide the eye.

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Figure 4 shows the temporally resolved peak emission intensity for the U I 591.53 nm and the UO 593.57 nm band. An exponential decay function was fit to the temporally resolved peak intensity of the two emission features from which we determine that the UO emission persists ~2 × longer compared to the ground state 591.53 nm U I emission. The measured persistence (1/e2) for U I and UO emission features are 7.3 µs and 13.5, µs respectively. The UO emission feature was observed at early times with significant intensity and continued to decrease (except for two outliers at 6 and 7 μs). The presence of UO molecules during the early times of plasma evolution could be related to the lower temperature of the plasma in fs LIBS in comparison to ns LIBS [23]. Figure 5 shows the ratio of the peak intensity of the 591.53 nm U I emission to the UO 593.57 nm peak intensity. The persistence of UO emission over the U I emission is highlighted in Fig. 5, where the ratio is below unity for the first 12 μs and then increases above unity as the hypothesized molecular emission dominates the emission spectrum.

 figure: Fig. 4

Fig. 4 Temporally resolved peak intensity of (a) U I 591.53 nm and (b) UO 593.57 nm emission lines with a constant gate width of 1.0 μs. The smooth curves in the figure are the exponential decay fit. The measurements were taken at atmospheric pressure.

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 figure: Fig. 5

Fig. 5 Temporally resolved molecular-to-atomic emission ratio for the emission lines referenced in Fig. 3 with a constant gate width of 1.0 μs under ambient atmospheric conditions.

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The effect of ambient pressure on the U and UO emission from the uranium plasma can be seen in Fig. 6. Both the U I emission and the uranium molecular emission intensity increase as the pressure initially increases, as shown in Fig. 6. However, at ~500 Torr the emission intensity begins to decrease for both species. The UO emission intensity at low (< 100 Torr) air pressures rapidly increases compared to the U emission intensity. For the lowest air pressure studied in this work (10 Torr), the UO emission intensity was less than the U emission intensity; however when the air pressure was increased to 50 – 100 Torr the UO emission intensity increased to about ~1.5X that of the U emission intensity. The increase in the UO emission intensity compared to the U emission intensity at low pressures suggests that an increase in the oxidation of U in the LA plasma occurs independent of confinement effects.

 figure: Fig. 6

Fig. 6 U I 593.38 nm and UO 593.57 peak emission intensity as a function of the ambient air pressure in the vacuum chamber.

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4. Discussion

A number of studies have reported on the LIBS emission spectra of uranium and uranium containing samples [10, 15, 35–37]; however, only one study to date has reported the uranium LIBS emission spectrum over a range of 100’s of nm [36]. From inspection of the available spectroscopic databases for U I & II emission, over 92,000 spectral lines are observed originating from ~1600 energy levels [29], and according to Palmer et al. [30] there are at least ~2800 emission lines in the 400–600 nm region shown in Fig. 2. In the work by Palmer et al., the authors limited the number of emission lines reported for U I & II, and a number of additional low intensity emission lines are observed in the reported spectra that are not tabulated in the text. The presence of a large number of emission lines results in a crowded emission spectrum, where interference between individual emission lines is possible [27, 35].

The fs laser plasmas typically exhibit reduced continuum emission with limited persistence in comparison with ns laser plasmas [7]. The spectral features given in Fig. 2 have been recorded at a delay of ~1 µs. However, even at this relatively long delay the background emission is significant, indicating that a large fraction of the baseline is in fact due to the overlap of the wings of interfering uranium emission lines and possible weaker unresolved uranium emission lines [35, 37]. Strong U I emission lines are observed for fs LA at 462.02, 502.74, 528.04, 562.07, and 591.53 nm. The most commonly reported uranium emission lines in the 400-600 nm region occur at 409.01, 424.17, 424.43, and 424.62 nm; the latter three emission lines are shown in the inset of Fig. 2(a). The 424.43 nm uranium ionic emission is commonly studied due to its relatively large isotope shift (~25 pm) [38]; however, as can be seen from Fig. 2, the signal-to-background ratio (SBR) is low compared to the strong emission lines mentioned above. This result highlights the need for improved spectral modeling and analysis of the uranium emission over large wavelength ranges in ns & fs LA plasmas.

In previous work by Barefield et al. [36], long pulse (ns) lasers pulses were used to ablate mixed oxide uranium containing samples over an acquisition spectral range of 300–600 nm. The acquisition of the spectra was delayed over the range of 1–4 μs following the laser pulse in order to reduce the influence of the prominent bremsstrahlung and recombination emission in the measured LIBS spectra. Compared to the previous ns LIBS spectra, the fs LIBS spectra in Fig. 2 exhibit a lower background and an overall reduced characteristic emission intensity; however, comparison of emission line intensities and behavior over the measured spectral window is not possible due to the lack of intensity correction in the ns LIBS results.

Compared to ns LA, fs LA results in a cooler, less dense plasma that exhibits reduced bremsstrahlung and recombination background emission as well as reduced spectral broadening [7]. The reduction in the background emission allows for the use of non-gated detectors and improved SBR for the measured emission lines [21, 39]. Due to the large number (1,000’s) of emission lines in the spectra of high-Z elements relevant to nuclear security, a reduction in the spectral broadening of the emission lines in fs LIBS measurements improves the potential for discerning the individual emission lines that may otherwise be convolved or overlapped in ns LIBS measurements. Further, as the isotope shift of both atomic and molecular emissions are of interest for uranium and other high-Z elements, the isotope shift-to-linewidth ratio must be considered as a figure of merit, quantifying the ability to resolve an isotope shift in the measured LIBS spectra. Based on the above discussion, fs LA offers a number of analytical merits compared to ns LA for the analysis of nuclear security relevant materials.

Figures 3 and 4 show the UO emission appears at later times when compared to atomic emission, and UO is predominant at later times of the plasma lifecycle. In laser-produced plasmas, the ionic species exist only at early times of the plasma evolution when the plasmas are hotter and hence the persistence of their characteristic emission is limited. Neutral emissions appear when the plasmas are cooler and can persist for longer times in comparison with ions. The plasma-assisted chemical reactions occur in the presence of an ambient atmosphere once the plasma has sufficiently cooled (~5000 K), which leads to production of excited molecular radicals [11, 25, 26]. Hence the appearance of molecular emission is delayed and the molecular emission can persist for longer times in comparison with emission from neutral and ionic species [7, 26]. The delay in the formation and observation of the radiating molecular species is shorter (~300–500 ns) for fs LA compared to ns LA (~5–10 µs) which could be the consequence of a range of conditions in fs LA, including the lower plasma temperatures, reduced thermal effects during ablation, increased ablation efficiency, weaker shock wave, etc [7, 26].

The intensity of both the U I and UO emission increases as the pressure initially increases and is shown in Fig. 6. The observed increase in the emission intensity as the gas pressure is increased has been explained as a result of a simultaneous increase in the number density and excitation temperature of the emitting species due to collisional confinement of the plasma by the ambient gas [40]. At 500 Torr the emission intensity begins to decrease for both U I and UO species, which is partially attributed to rapid collisional cooling of the plasma and self-absorption in the high density U plasma at higher ambient air pressures [41]. The decrease in the uranium atomic and molecular emission as the pressure was increased above ~400 Torr can be further explained by the preferential formation of complex uranium oxides (UxOy) at higher air pressures [25].

The oxidation of uranium and the formation of complex uranium oxides in LA plasmas has not been studied extensively in the literature, and the formation and depletion mechanisms of UO in a laser produced uranium plasma is unknown. It has to be mentioned that the oxidation in a transient laser-plasma system expanding into an ambient is dictated by diffusion of oxygen molecules into the plasma, strength of the shockwaves which hinder plasma-ambient interaction and plume thermodynamics. A simplified version of the gas-phase chemistry for the reaction of atomic U with O2 can be represented by the following reaction pathways:

U+O2UO+O
UO+O2UO2+O
UO2+O2UO3+O
Based on cross-molecular beam and rare-gas matrix spectroscopy studies with laser ablation [42–44], reaction (1) has a small activation barrier and proceeds at a hard sphere collision rate at thermal energies. No rate constant data is available in the literature for reaction (2), however, and Wormhoudt et al. assumed that the reaction rates for (2) and (3) were the same based on the comparable reaction exothermicities. These values were set to half that of the hard sphere collision rate [25]. Setting the reaction rate constant for reaction (3) to a smaller value than reaction (1) is in agreement with the observation in matrix isolation studies in Ar that significant UO3 formation was only possible after UV irradiation of the matrix sample [43]. Taken together, this information on the reaction of atomic uranium with O2, increasing the O2 number density increases the rate of consumption of both U and UO, leading to the generation of the larger UO2 and UO3 oxides. An attempt has been made in this work to elucidate the formation and evolution of UO within fs LA plasmas; however, due to experimental limitations we were not able to identify the specific reaction pathway(s) for UO formation and the possible depletion mechanisms discussed above. In addition, it is important to note that the emission intensity of both U and UO are sensitive to the excitation temperature within plasma. Further studies are needed to isolate and measure the time-dependence of atomic and molecular number densities within the expanding plume; for example using absorption-based measurements.

The reaction of U with N2 present in air to form NUN is possible through an insertion mechanism [45]. The dissociation bond strength for UO compared to O2 favors reaction of U with O2 to form UO; however, atomic uranium cannot abstract a nitrogen atom from N2 as the reaction is endothermic and the required activation energy for this reaction (>99 ± 5 kcal/mol) is not likely to be provided by hypothermal uranium atoms in the plasma plume [45]. Further, the insertion reaction required to form NUN is only slightly exothermic compared to the significantly exothermic uranium oxidation reaction (222 ± 7 kcal/mol) shown above in reaction (1) [45]. This is also supported by the fact that our recent laser absorption studies showed that the persistence of the U ground state population is significantly reduced in the presence of air compared to nitrogen environment [15].

The UO/U line intensity ratio is found to peak at ~100 Torr air pressure (Fig. 6). The rapid cooling and expansion of the inhomogeneous plasma plume into the ambient atmosphere results in complex plasma dynamics and occurrence of plasma-assisted chemical reactions. The reaction pathways, rates, and temperatures of formation are not well understood for most of the possible plasma assisted chemical reactions that can take place within the expanding uranium plasma plume, and a limited number of studies have been performed on this topic [17, 20, 22, 23]. As the ambient air pressure is increased, preferential formation of both simple diatomic and complex polyatomic oxide molecules occurs, which depletes the atomic population density within the plasma plume [4, 15, 46].

In the fs LIBS results reported in this work, only the strong Q branch UO emission feature is observed due to the weaker emission intensities of the P and R branch emissions and the high temperatures present during the emission [26, 34]. Further, the complex spectrum consisting of atomic, ionic, and molecular emissions could lead to the additional emission branches being overlapped by atomic or ionic emission features. Lastly, the rotational structure in the Q branch is not resolved in the measured fs LIBS spectra due to the relatively strong broadening of the individual emission lines and close spacing of these emissions in the Q branch for UO.

5. Summary

We investigated the temporal evolution of uranium containing plasmas using optical emission spectroscopy under a number of ambient air pressures. A 200 nm wide spectral scan of the uranium emission originating from fs LA produced plasmas is reported and was compared to previous work available in the literature on ns LA of uranium containing samples. The spectral emission features showed the presence of atomic, ionic, and molecular uranium species from fs LA plasmas. The presence of a UO molecular emission feature at 593.57 nm in the fs LIBS plasma was confirmed through analysis of the temporally resolved emission spectra, the dependence of the emission spectra on the ambient gas pressure, and the previous work on uranium oxide emission and formation reported in the open literature. The enhancement of the uranium molecular emission intensity as the ambient air pressure was increased, along with the greater persistence of the molecular emission compared to the atomic emission, confirms that the emission originates from a molecular transition within the fs LA plasma.

Even though the fs LA provided reduced continuum emission, a significant background emission can be seen in the recorded spectral features. The presence of a large number of emission lines in the spectra results in a crowded emission spectrum, where interference between individual emission lines is possible. Hence strong background emission that appears as spectral features could be the result of the overlap of uranium emission lines. Extensive LIBS work exists in the literature on isotopic separation of the U atomic emission lines; however, the emission lines which exhibit the strongest known isotope shift have a considerably lower SBR (SBR = 1.5 for 424.43 nm) compared to the strongest observed atomic emission lines (SBR = 8 for 591.53 nm) in the 400 – 600 nm region [29, 38]. These results highlight the need for improved spectral modeling and analysis of the uranium emission over large wavelength ranges in fs LA plasmas.

Previous work by our group [15] has shown that the magnitude and persistence of the uranium absorption signal are significantly reduced in air compared to N2 environment. The present results show that the presence of oxygen in the ambient environment promotes formation of molecular species through an oxidation process. The oxidation process removes ground state atomic uranium from the system, which explains the observed decrease in the uranium absorption signal in our previous work. The intensity of both the U I and UO emission increases as the pressure increases; however, at higher pressure (500 Torr), a reduction in signal intensity is seen for both species. Additional plasma-assisted chemical reactions can result in the formation of more complex uranium oxide (UxOy) molecules that could reduce the emission intensity of both the neutral atomic and UO species. Although our studies showed the presence of strong UO band in fs LA plumes and its time evolution, the detailed chemical reaction pathways for UO are still unknown. Hence further work must be conducted to investigate the formation of UO in fs LA plasmas under a range of absolute oxygen concentrations and independent of any plasma confinement effects in the measurement. Finally, the present work is very relevant to the LIF, LA-LAS, LIBS, and LA-ICP-MS communities, where generation of oxides within the LA plasma affects the population density of the species of interest.

6. Funding and Acknowledgments

This work is supported in part by the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) Office of Defense Nuclear Nonproliferation and Verification Research and Development (NA-22). This work was funded in part by the Consortium for Verification Technology under U.S. Department of Energy National Nuclear Security Administration Award Number DE-NA0002534 and by the U.S. Department of Homeland Security under Grant Award Number 2012.05 DN-130-NF0001. Pacific Northwest National Laboratory is operated for the U.S. DOE by the Battelle Memorial Institute under Contract No. DE-AC05-76RLO1830. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Department of Homeland Security.

The authors would like to acknowledge the Pennsylvania State University Environmental Health and Safety’s Radiation Protection Office for their support in licensing the experimental facilities and obtaining the uranium samples used in this work as well as the staff of the Pennsylvania State University’s Radiation Science and Engineering Center for assisting with gaining access to uranium samples. The authors would like to personally thank and acknowledge Radiation Safety Officer Jeff Leavey, who passed away shortly before this work was completed and was involved in the licensing and regulation of our laboratory space.

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9. I. Ghebregziabher, K. C. Hartig, and I. Jovanovic, “Propagation distance-resolved characteristics of filament-induced copper plasma,” Opt. Express 24(5), 5263 (2016). [CrossRef]  

10. P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016). [CrossRef]  

11. C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002). [CrossRef]  

12. H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998). [CrossRef]  

13. D. A. Cremers, A. Beddingfield, R. Smithwick, R. C. Chinni, C. R. Jones, B. Beardsley, and L. Karch, “Monitoring uranium, hydrogen, and lithium and their isotopes using a compact laser-induced breakdown spectroscopy (LIBS) probe and high-resolution spectrometer,” Appl. Spectrosc. 66(3), 250–261 (2012). [CrossRef]   [PubMed]  

14. A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016). [CrossRef]  

15. P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016). [CrossRef]  

16. R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011). [CrossRef]  

17. D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015). [CrossRef]  

18. R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015). [CrossRef]   [PubMed]  

19. J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016). [CrossRef]   [PubMed]  

20. S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016). [CrossRef]   [PubMed]  

21. B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013). [CrossRef]  

22. M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014). [CrossRef]  

23. S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016). [CrossRef]  

24. J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015). [CrossRef]  

25. J. Wormhoudt, “Uranium oxide gaseous ion and neutral infrared spectroscopy,” (Aerodyne Research, Inc., 1983).

26. L. A. Kaledin and M. C. Heaven, “Electronic Spectroscopy of UO,” J. Mol. Spectrosc. 185(1), 1–7 (1997). [CrossRef]   [PubMed]  

27. S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015). [CrossRef]  

28. S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016). [CrossRef]   [PubMed]  

29. J. Blaise and L. J. Radziemski, “Energy levels of neutral atomic uranium (Ui),” J. Opt. Soc. Am. 66(7), 644–659 (1976). [CrossRef]  

30. B. A. Palmer, R. A. Keller, and J. R. Engleman, “An atlas of uranium emissions intensities in a hollow cathode discharge,” (Los Alamos Scientific Laboratory, 1980).

31. R. L. Kurucz and B. Bell, “1995 Atomic Line Data: CD-ROM 23” (2016), retrieved http://www.cfa.harvard.edu/amp/ampdata/kurucz23/sekur.html/.

32. A. Kramida, Y. Ralchenko, J. Reader, and NIST ASD Team, “NIST Atomic Spectra Database (ver. 5.3) [Online],” (National Institute of Standards and Technology, Gaithersburg, MD).

33. I. Grenthe, J. Drożdżyński, T. Fujino, E. C. Buck, T. E. Albrecht-Schmitt, and S. F. Wolf, Uranium*, in The Chemistry of the Actinide and Transactinide Elements, L. R. Morss, N. M. Edelstein, and J. Fuger, eds. (Springer Netherlands, Dordrecht, 2011), pp. 253–698.

34. M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985). [CrossRef]  

35. I. Choi, G. C. Chan, X. Mao, D. L. Perry, and R. E. Russo, “Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS),” Appl. Spectrosc. 67(11), 1275–1284 (2013). [CrossRef]   [PubMed]  

36. J. E. Barefield 2nd, E. J. Judge, J. M. Berg, S. P. Willson, L. A. Le, and L. N. Lopez, “Analysis and spectral assignments of mixed actinide oxide samples using Laser-Induced Breakdown Spectroscopy (LIBS),” Appl. Spectrosc. 67(4), 433–440 (2013). [CrossRef]   [PubMed]  

37. R. C. Chinni, D. A. Cremers, L. J. Radziemski, M. Bostian, and C. Navarro-Northrup, “Detection of Uranium Using Laser-Induced Breakdown Spectroscopy,” Appl. Spectrosc. 63(11), 1238–1250 (2009). [CrossRef]   [PubMed]  

38. J. Blaise, J.-F. Wyart, J. Vergès, R. Engleman Jr, B. A. Palmer, and L. J. Radziemski, “Energy levels and isotope shifts for singly ionized uranium (U II),” J. Opt. Soc. Am. B 11(10), 1897–1929 (1994). [CrossRef]  

39. A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008). [CrossRef]  

40. S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015). [CrossRef]  

41. D. E. Kim, K. J. Yoo, H. K. Park, K. J. Oh, and D. W. Kim, “Quantitative analysis of aluminum impurities in zinc alloy by laser-induced breakdown spectroscopy,” Appl. Spectrosc. 51(1), 22–29 (1997). [CrossRef]  

42. W. L. Fite, H. H. Lo, and P. Irving, “Associative ionization in U+O and U+O2 collisions,” J. Chem. Phys. 60(4), 1236–1250 (1974). [CrossRef]  

43. R. D. Hunt and L. Andrews, “Reactions of Pulsed-laser evaporated uranium atoms with molecular-oxygen - infrared-spectra of Uo, Uo2, Uo3, Uo2+, Uo22+, and Uo3-O2 in solid argon,” J. Chem. Phys. 98(5), 3690–3696 (1993). [CrossRef]  

44. R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994). [CrossRef]  

45. R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993). [CrossRef]  

46. S. S. Harilal, N. L. LaHaye, and M. C. Phillips, “Two-dimensional fluorescence spectroscopy of laser-produced plasmas,” Opt. Lett. 41(15), 3547–3550 (2016). [CrossRef]   [PubMed]  

References

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  1. W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).
  2. D. W. Hahn and N. Omenetto, “Laser-Induced Breakdown Spectroscopy (LIBS), Part II: review of instrumental and methodological approaches to material analysis and applications to different fields,” Appl. Spectrosc. 66(4), 347–419 (2012).
    [Crossref] [PubMed]
  3. N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
    [Crossref]
  4. N. R. Taylor and M. C. Phillips, “Differential laser absorption spectroscopy of uranium in an atmospheric pressure laser-induced plasma,” Opt. Lett. 39(3), 594–597 (2014).
    [Crossref] [PubMed]
  5. T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
    [Crossref]
  6. J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
    [Crossref]
  7. E. L. Gurevich and R. Hergenröder, “Femtosecond laser-induced breakdown spectroscopy: physics, applications, and perspectives,” Appl. Spectrosc. 61(10), 233A–242A (2007).
    [Crossref] [PubMed]
  8. H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
    [Crossref]
  9. I. Ghebregziabher, K. C. Hartig, and I. Jovanovic, “Propagation distance-resolved characteristics of filament-induced copper plasma,” Opt. Express 24(5), 5263 (2016).
    [Crossref]
  10. P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016).
    [Crossref]
  11. C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002).
    [Crossref]
  12. H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998).
    [Crossref]
  13. D. A. Cremers, A. Beddingfield, R. Smithwick, R. C. Chinni, C. R. Jones, B. Beardsley, and L. Karch, “Monitoring uranium, hydrogen, and lithium and their isotopes using a compact laser-induced breakdown spectroscopy (LIBS) probe and high-resolution spectrometer,” Appl. Spectrosc. 66(3), 250–261 (2012).
    [Crossref] [PubMed]
  14. A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
    [Crossref]
  15. P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
    [Crossref]
  16. R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
    [Crossref]
  17. D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
    [Crossref]
  18. R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015).
    [Crossref] [PubMed]
  19. J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016).
    [Crossref] [PubMed]
  20. S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
    [Crossref] [PubMed]
  21. B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
    [Crossref]
  22. M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
    [Crossref]
  23. S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
    [Crossref]
  24. J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015).
    [Crossref]
  25. J. Wormhoudt, “Uranium oxide gaseous ion and neutral infrared spectroscopy,” (Aerodyne Research, Inc., 1983).
  26. L. A. Kaledin and M. C. Heaven, “Electronic Spectroscopy of UO,” J. Mol. Spectrosc. 185(1), 1–7 (1997).
    [Crossref] [PubMed]
  27. S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
    [Crossref]
  28. S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016).
    [Crossref] [PubMed]
  29. J. Blaise and L. J. Radziemski, “Energy levels of neutral atomic uranium (Ui),” J. Opt. Soc. Am. 66(7), 644–659 (1976).
    [Crossref]
  30. B. A. Palmer, R. A. Keller, and J. R. Engleman, “An atlas of uranium emissions intensities in a hollow cathode discharge,” (Los Alamos Scientific Laboratory, 1980).
  31. R. L. Kurucz and B. Bell, “1995 Atomic Line Data: CD-ROM 23” (2016), retrieved http://www.cfa.harvard.edu/amp/ampdata/kurucz23/sekur.html/ .
  32. A. Kramida, Y. Ralchenko, J. Reader, and NIST ASD Team, “NIST Atomic Spectra Database (ver. 5.3) [Online],” (National Institute of Standards and Technology, Gaithersburg, MD).
  33. I. Grenthe, J. Drożdżyński, T. Fujino, E. C. Buck, T. E. Albrecht-Schmitt, and S. F. Wolf, Uranium*, in The Chemistry of the Actinide and Transactinide Elements, L. R. Morss, N. M. Edelstein, and J. Fuger, eds. (Springer Netherlands, Dordrecht, 2011), pp. 253–698.
  34. M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
    [Crossref]
  35. I. Choi, G. C. Chan, X. Mao, D. L. Perry, and R. E. Russo, “Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS),” Appl. Spectrosc. 67(11), 1275–1284 (2013).
    [Crossref] [PubMed]
  36. J. E. Barefield, E. J. Judge, J. M. Berg, S. P. Willson, L. A. Le, and L. N. Lopez, “Analysis and spectral assignments of mixed actinide oxide samples using Laser-Induced Breakdown Spectroscopy (LIBS),” Appl. Spectrosc. 67(4), 433–440 (2013).
    [Crossref] [PubMed]
  37. R. C. Chinni, D. A. Cremers, L. J. Radziemski, M. Bostian, and C. Navarro-Northrup, “Detection of Uranium Using Laser-Induced Breakdown Spectroscopy,” Appl. Spectrosc. 63(11), 1238–1250 (2009).
    [Crossref] [PubMed]
  38. J. Blaise, J.-F. Wyart, J. Vergès, R. Engleman, B. A. Palmer, and L. J. Radziemski, “Energy levels and isotope shifts for singly ionized uranium (U II),” J. Opt. Soc. Am. B 11(10), 1897–1929 (1994).
    [Crossref]
  39. A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
    [Crossref]
  40. S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
    [Crossref]
  41. D. E. Kim, K. J. Yoo, H. K. Park, K. J. Oh, and D. W. Kim, “Quantitative analysis of aluminum impurities in zinc alloy by laser-induced breakdown spectroscopy,” Appl. Spectrosc. 51(1), 22–29 (1997).
    [Crossref]
  42. W. L. Fite, H. H. Lo, and P. Irving, “Associative ionization in U+O and U+O2 collisions,” J. Chem. Phys. 60(4), 1236–1250 (1974).
    [Crossref]
  43. R. D. Hunt and L. Andrews, “Reactions of Pulsed-laser evaporated uranium atoms with molecular-oxygen - infrared-spectra of Uo, Uo2, Uo3, Uo2+, Uo22+, and Uo3-O2 in solid argon,” J. Chem. Phys. 98(5), 3690–3696 (1993).
    [Crossref]
  44. R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
    [Crossref]
  45. R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993).
    [Crossref]
  46. S. S. Harilal, N. L. LaHaye, and M. C. Phillips, “Two-dimensional fluorescence spectroscopy of laser-produced plasmas,” Opt. Lett. 41(15), 3547–3550 (2016).
    [Crossref] [PubMed]

2016 (11)

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
[Crossref]

I. Ghebregziabher, K. C. Hartig, and I. Jovanovic, “Propagation distance-resolved characteristics of filament-induced copper plasma,” Opt. Express 24(5), 5263 (2016).
[Crossref]

P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016).
[Crossref]

A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
[Crossref]

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016).
[Crossref] [PubMed]

S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
[Crossref] [PubMed]

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016).
[Crossref] [PubMed]

S. S. Harilal, N. L. LaHaye, and M. C. Phillips, “Two-dimensional fluorescence spectroscopy of laser-produced plasmas,” Opt. Lett. 41(15), 3547–3550 (2016).
[Crossref] [PubMed]

2015 (6)

J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
[Crossref]

R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015).
[Crossref] [PubMed]

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

2014 (3)

N. R. Taylor and M. C. Phillips, “Differential laser absorption spectroscopy of uranium in an atmospheric pressure laser-induced plasma,” Opt. Lett. 39(3), 594–597 (2014).
[Crossref] [PubMed]

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

2013 (3)

2012 (2)

2011 (1)

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

2009 (1)

2008 (1)

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

2007 (1)

2006 (1)

J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
[Crossref]

2002 (1)

C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002).
[Crossref]

1998 (1)

H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998).
[Crossref]

1997 (2)

1994 (2)

J. Blaise, J.-F. Wyart, J. Vergès, R. Engleman, B. A. Palmer, and L. J. Radziemski, “Energy levels and isotope shifts for singly ionized uranium (U II),” J. Opt. Soc. Am. B 11(10), 1897–1929 (1994).
[Crossref]

R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
[Crossref]

1993 (2)

R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993).
[Crossref]

R. D. Hunt and L. Andrews, “Reactions of Pulsed-laser evaporated uranium atoms with molecular-oxygen - infrared-spectra of Uo, Uo2, Uo3, Uo2+, Uo22+, and Uo3-O2 in solid argon,” J. Chem. Phys. 98(5), 3690–3696 (1993).
[Crossref]

1985 (1)

M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
[Crossref]

1976 (1)

1974 (1)

W. L. Fite, H. H. Lo, and P. Irving, “Associative ionization in U+O and U+O2 collisions,” J. Chem. Phys. 60(4), 1236–1250 (1974).
[Crossref]

Ahn, S.-H.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Andrews, L.

R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
[Crossref]

R. D. Hunt and L. Andrews, “Reactions of Pulsed-laser evaporated uranium atoms with molecular-oxygen - infrared-spectra of Uo, Uo2, Uo3, Uo2+, Uo22+, and Uo3-O2 in solid argon,” J. Chem. Phys. 98(5), 3690–3696 (1993).
[Crossref]

R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993).
[Crossref]

Anglos, D.

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

Barefield, J. E.

Beardsley, B.

Beddingfield, A.

Berg, J. M.

Blaise, J.

Bol’shakov, A. A.

A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
[Crossref]

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

Bostian, M.

Brumfield, B. E.

S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016).
[Crossref] [PubMed]

S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
[Crossref] [PubMed]

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

Cannon, B. D.

S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
[Crossref] [PubMed]

Chan, G. C.

Chan, G. C. Y.

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

Chinni, R. C.

Choi, I.

Choi, J.-O.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Chu, W.-S.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Cremers, D. A.

Diwakar, P. M.

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

Dong, M.

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

Duffin, A. M.

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

Eiden, G. C.

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

Elhassan, A.

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

Engleman, R.

Fite, W. L.

W. L. Fite, H. H. Lo, and P. Irving, “Associative ionization in U+O and U+O2 collisions,” J. Chem. Phys. 60(4), 1236–1250 (1974).
[Crossref]

Ghebregziabher, I.

Giakoumaki, A.

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

Glaus, R.

R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015).
[Crossref] [PubMed]

Gonzalez, J. J.

A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
[Crossref]

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

Gornushkin, I.

R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015).
[Crossref] [PubMed]

Gunther, D.

J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
[Crossref]

Gurevich, E. L.

Hahn, D. W.

Harilal, S. S.

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
[Crossref] [PubMed]

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016).
[Crossref] [PubMed]

S. S. Harilal, N. L. LaHaye, and M. C. Phillips, “Two-dimensional fluorescence spectroscopy of laser-produced plasmas,” Opt. Lett. 41(15), 3547–3550 (2016).
[Crossref] [PubMed]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

Harith, M. A.

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

Hartig, K. C.

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

I. Ghebregziabher, K. C. Hartig, and I. Jovanovic, “Propagation distance-resolved characteristics of filament-induced copper plasma,” Opt. Express 24(5), 5263 (2016).
[Crossref]

B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
[Crossref]

Heaven, M. C.

L. A. Kaledin and M. C. Heaven, “Electronic Spectroscopy of UO,” J. Mol. Spectrosc. 185(1), 1–7 (1997).
[Crossref] [PubMed]

M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
[Crossref]

Hergenröder, R.

Hou, H.

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

Hunt, R. D.

R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
[Crossref]

R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993).
[Crossref]

R. D. Hunt and L. Andrews, “Reactions of Pulsed-laser evaporated uranium atoms with molecular-oxygen - infrared-spectra of Uo, Uo2, Uo3, Uo2+, Uo22+, and Uo3-O2 in solid argon,” J. Chem. Phys. 98(5), 3690–3696 (1993).
[Crossref]

Ilyin, A. A.

T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
[Crossref]

Ingo, G. M.

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

Irving, P.

W. L. Fite, H. H. Lo, and P. Irving, “Associative ionization in U+O and U+O2 collisions,” J. Chem. Phys. 60(4), 1236–1250 (1974).
[Crossref]

Jang, K.-H.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Javier Laserna, J.

J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016).
[Crossref] [PubMed]

Jones, C. R.

Jovanovic, I.

P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016).
[Crossref]

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

I. Ghebregziabher, K. C. Hartig, and I. Jovanovic, “Propagation distance-resolved characteristics of filament-induced copper plasma,” Opt. Express 24(5), 5263 (2016).
[Crossref]

B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
[Crossref]

Judge, E. J.

Kaledin, L. A.

L. A. Kaledin and M. C. Heaven, “Electronic Spectroscopy of UO,” J. Mol. Spectrosc. 185(1), 1–7 (1997).
[Crossref] [PubMed]

Karch, L.

Kim, C.-S.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Kim, D. E.

Kim, D. W.

Kitazima, I.

H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998).
[Crossref]

Ko, P.

B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
[Crossref]

Koch, J.

J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
[Crossref]

Labutin, T. A.

T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
[Crossref]

LaHaye, N. L.

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

S. S. Harilal, N. L. LaHaye, and M. C. Phillips, “Two-dimensional fluorescence spectroscopy of laser-produced plasmas,” Opt. Lett. 41(15), 3547–3550 (2016).
[Crossref] [PubMed]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

Laserna, J. J.

J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015).
[Crossref]

Le, L. A.

Lednev, V. N.

T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
[Crossref]

Lee, H.-T.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Lo, H. H.

W. L. Fite, H. H. Lo, and P. Irving, “Associative ionization in U+O and U+O2 collisions,” J. Chem. Phys. 60(4), 1236–1250 (1974).
[Crossref]

Lopez, L. N.

Lu, J.

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

Ma, X. W.

D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
[Crossref]

Mao, X.

A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
[Crossref]

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

I. Choi, G. C. Chan, X. Mao, D. L. Perry, and R. E. Russo, “Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS),” Appl. Spectrosc. 67(11), 1275–1284 (2013).
[Crossref] [PubMed]

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

Martinez, M. A.

C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002).
[Crossref]

McKay, C. P.

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

McNutt, J.

B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
[Crossref]

Morgan, P. K.

P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016).
[Crossref]

Moros, J.

J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016).
[Crossref] [PubMed]

J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015).
[Crossref]

Navarro-Northrup, C.

Nicolai, J. P.

M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
[Crossref]

Niki, H.

H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998).
[Crossref]

Oh, K. J.

Omenetto, N.

Palmer, B. A.

Park, H. K.

Park, J.-I.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Parks, E. K.

M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
[Crossref]

Perry, D. L.

I. Choi, G. C. Chan, X. Mao, D. L. Perry, and R. E. Russo, “Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS),” Appl. Spectrosc. 67(11), 1275–1284 (2013).
[Crossref] [PubMed]

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

Phillips, M. C.

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016).
[Crossref] [PubMed]

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
[Crossref] [PubMed]

S. S. Harilal, N. L. LaHaye, and M. C. Phillips, “Two-dimensional fluorescence spectroscopy of laser-produced plasmas,” Opt. Lett. 41(15), 3547–3550 (2016).
[Crossref] [PubMed]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

N. R. Taylor and M. C. Phillips, “Differential laser absorption spectroscopy of uranium in an atmospheric pressure laser-induced plasma,” Opt. Lett. 39(3), 594–597 (2014).
[Crossref] [PubMed]

Pisonero, J.

J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
[Crossref]

Popov, A. M.

T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
[Crossref]

Radziemski, L. J.

Riedel, J.

R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015).
[Crossref] [PubMed]

Riley, S. J.

M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
[Crossref]

Robbiola, L.

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

Russo, R. E.

A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
[Crossref]

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

I. Choi, G. C. Chan, X. Mao, D. L. Perry, and R. E. Russo, “Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS),” Appl. Spectrosc. 67(11), 1275–1284 (2013).
[Crossref] [PubMed]

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

Scott, J. R.

P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016).
[Crossref]

Serrano, J.

J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016).
[Crossref] [PubMed]

J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015).
[Crossref]

Shah, N. P.

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

Skrodzki, P. J.

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

Smith, C. A.

C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002).
[Crossref]

Smithwick, R.

Song, J.-H.

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

Sorkhabi, O.

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

Suter, J. D.

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

Taylor, N.

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

Taylor, N. R.

Toth, L. M.

R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
[Crossref]

Veirs, D. K.

C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002).
[Crossref]

Vergès, J.

Walle, M.

J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
[Crossref]

Wang, S. L.

D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
[Crossref]

Willson, S. P.

Wyart, J.-F.

Yasuda, T.

H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998).
[Crossref]

Yeak, J.

S. S. Harilal, J. Yeak, B. E. Brumfield, and M. C. Phillips, “Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy,” Opt. Express 24(16), 17941–17949 (2016).
[Crossref] [PubMed]

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

Yee, B.

B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
[Crossref]

Yoo, K. J.

Yustein, J. T.

R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
[Crossref]

R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993).
[Crossref]

Zhang, D. C.

D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
[Crossref]

Zheng, R.

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

Zhu, X. L.

D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
[Crossref]

Zorba, V.

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

AIP Conf. Proc. (1)

R. D. Hunt, L. M. Toth, J. T. Yustein, and L. Andrews, “Matrix-isolation infrared-spectra of O2 and N2 insertion reactions with atomic uranium,” AIP Conf. Proc. 288, 148–152 (1994).
[Crossref]

Anal. Chem. (2)

R. Glaus, J. Riedel, and I. Gornushkin, “Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples,” Anal. Chem. 87(19), 10131–10137 (2015).
[Crossref] [PubMed]

S. S. Harilal, B. E. Brumfield, B. D. Cannon, and M. C. Phillips, “Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas,” Anal. Chem. 88(4), 2296–2302 (2016).
[Crossref] [PubMed]

Appl. Spectrosc. (7)

I. Choi, G. C. Chan, X. Mao, D. L. Perry, and R. E. Russo, “Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS),” Appl. Spectrosc. 67(11), 1275–1284 (2013).
[Crossref] [PubMed]

J. E. Barefield, E. J. Judge, J. M. Berg, S. P. Willson, L. A. Le, and L. N. Lopez, “Analysis and spectral assignments of mixed actinide oxide samples using Laser-Induced Breakdown Spectroscopy (LIBS),” Appl. Spectrosc. 67(4), 433–440 (2013).
[Crossref] [PubMed]

R. C. Chinni, D. A. Cremers, L. J. Radziemski, M. Bostian, and C. Navarro-Northrup, “Detection of Uranium Using Laser-Induced Breakdown Spectroscopy,” Appl. Spectrosc. 63(11), 1238–1250 (2009).
[Crossref] [PubMed]

D. A. Cremers, A. Beddingfield, R. Smithwick, R. C. Chinni, C. R. Jones, B. Beardsley, and L. Karch, “Monitoring uranium, hydrogen, and lithium and their isotopes using a compact laser-induced breakdown spectroscopy (LIBS) probe and high-resolution spectrometer,” Appl. Spectrosc. 66(3), 250–261 (2012).
[Crossref] [PubMed]

D. W. Hahn and N. Omenetto, “Laser-Induced Breakdown Spectroscopy (LIBS), Part II: review of instrumental and methodological approaches to material analysis and applications to different fields,” Appl. Spectrosc. 66(4), 347–419 (2012).
[Crossref] [PubMed]

E. L. Gurevich and R. Hergenröder, “Femtosecond laser-induced breakdown spectroscopy: physics, applications, and perspectives,” Appl. Spectrosc. 61(10), 233A–242A (2007).
[Crossref] [PubMed]

D. E. Kim, K. J. Yoo, H. K. Park, K. J. Oh, and D. W. Kim, “Quantitative analysis of aluminum impurities in zinc alloy by laser-induced breakdown spectroscopy,” Appl. Spectrosc. 51(1), 22–29 (1997).
[Crossref]

Chem. Phys. Lett. (1)

M. C. Heaven, J. P. Nicolai, S. J. Riley, and E. K. Parks, “Rotationally Resolved Electronic-Spectra for Uranium Monoxide,” Chem. Phys. Lett. 119(2-3), 229–233 (1985).
[Crossref]

Int. J. of Precis. Eng. Manuf.- Green Tech. (1)

W.-S. Chu, C.-S. Kim, H.-T. Lee, J.-O. Choi, J.-I. Park, J.-H. Song, K.-H. Jang, and S.-H. Ahn, “Hybrid manufacturing in micro/nano scale: A Review,” Int. J. of Precis. Eng. Manuf.- Green Tech. 1, 75–92 (2014).

J. Anal. At. Spectrom. (6)

A. A. Bol’shakov, X. Mao, J. J. Gonzalez, and R. E. Russo, “Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art,” J. Anal. At. Spectrom. 31(1), 119–134 (2016).
[Crossref]

N. L. LaHaye, M. C. Phillips, A. M. Duffin, G. C. Eiden, and S. S. Harilal, “The influence of ns- and fs-LA plume local conditions on the performance of a combined LIBS/LA-ICP-MS sensor,” J. Anal. At. Spectrom. 31(2), 515–522 (2016).
[Crossref]

T. A. Labutin, V. N. Lednev, A. A. Ilyin, and A. M. Popov, “Femtosecond laser-induced breakdown spectroscopy,” J. Anal. At. Spectrom. 31(1), 90–118 (2016).
[Crossref]

J. Koch, M. Walle, J. Pisonero, and D. Gunther, “Performance characteristics of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry at ∼265 and ∼200 nm,” J. Anal. At. Spectrom. 21(9), 932–940 (2006).
[Crossref]

S. S. Harilal, J. Yeak, B. E. Brumfield, J. D. Suter, and M. C. Phillips, “Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas,” J. Anal. At. Spectrom. 31(6), 1192–1197 (2016).
[Crossref]

J. Serrano, J. Moros, and J. J. Laserna, “Exploring the formation routes of diatomic hydrogenated radicals using femtosecond laser-induced breakdown spectroscopy of deuterated molecular solids,” J. Anal. At. Spectrom. 30(11), 2343–2352 (2015).
[Crossref]

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[Crossref]

R. D. Hunt, J. T. Yustein, and L. Andrews, “Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen,” J. Chem. Phys. 98(8), 6070–6074 (1993).
[Crossref]

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[Crossref] [PubMed]

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H. Niki, T. Yasuda, and I. Kitazima, “Measurement technique of boron isotopic ratio by laser-induced breakdown spectroscopy,” J. Nucl. Sci. Technol. 35(1), 34–39 (1998).
[Crossref]

J. Opt. Soc. Am. (1)

J. Opt. Soc. Am. B (1)

Opt. Express (2)

Opt. Lett. (2)

Phys. Chem. Chem. Phys. (1)

J. Serrano, J. Moros, and J. Javier Laserna, “Molecular signatures in femtosecond laser-induced organic plasmas: comparison with nanosecond laser ablation,” Phys. Chem. Chem. Phys. 18(4), 2398–2408 (2016).
[Crossref] [PubMed]

Plasma Sci. Technol. (1)

D. C. Zhang, X. W. Ma, S. L. Wang, and X. L. Zhu, “Influence of ambient gas on laser-induced breakdown spectroscopy of uranium metal,” Plasma Sci. Technol. 17(11), 971–974 (2015).
[Crossref]

Spectrochim. Acta B At. Spectrosc. (10)

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

B. Yee, K. C. Hartig, P. Ko, J. McNutt, and I. Jovanovic, “Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma,” Spectrochim. Acta B At. Spectrosc. 79–80, 72–76 (2013).
[Crossref]

M. Dong, G. C. Y. Chan, X. Mao, J. J. Gonzalez, J. Lu, and R. E. Russo, “Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio,” Spectrochim. Acta B At. Spectrosc. 100, 62–69 (2014).
[Crossref]

A. Elhassan, A. Giakoumaki, D. Anglos, G. M. Ingo, L. Robbiola, and M. A. Harith, “Nanosecond and femtosecond Laser Induced Breakdown Spectroscopic analysis of bronze alloys,” Spectrochim. Acta B At. Spectrosc. 63(4), 504–511 (2008).
[Crossref]

S. S. Harilal, P. M. Diwakar, N. L. LaHaye, and M. C. Phillips, “Spatio-temporal evolution of uranium emission in laser-produced plasmas,” Spectrochim. Acta B At. Spectrosc. 111, 1–7 (2015).
[Crossref]

P. J. Skrodzki, N. P. Shah, N. Taylor, K. C. Hartig, N. L. LaHaye, B. E. Brumfield, I. Jovanovic, M. C. Phillips, and S. S. Harilal, “Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas,” Spectrochim. Acta B At. Spectrosc. 125, 112–119 (2016).
[Crossref]

R. E. Russo, A. A. Bol’shakov, X. Mao, C. P. McKay, D. L. Perry, and O. Sorkhabi, “Laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 66(2), 99–104 (2011).
[Crossref]

P. K. Morgan, J. R. Scott, and I. Jovanovic, “Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma,” Spectrochim. Acta B At. Spectrosc. 116, 58–62 (2016).
[Crossref]

C. A. Smith, M. A. Martinez, D. K. Veirs, and D. A. Cremers, “Pu-239/Pu-240 isotope ratios determined using high resolution emission spectroscopy in a laser-induced plasma,” Spectrochim. Acta B At. Spectrosc. 57(5), 929–937 (2002).
[Crossref]

H. Hou, G. C. Y. Chan, X. Mao, R. Zheng, V. Zorba, and R. E. Russo, “Femtosecond filament-laser ablation molecular isotopic spectrometry,” Spectrochim. Acta B At. Spectrosc. 113, 113–118 (2015).
[Crossref]

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Figures (6)

Fig. 1
Fig. 1 Simplified schematic of the experimental setup utilized in this work, which is licensed for laser ablation analysis of radioactive and special nuclear materials (SNM).
Fig. 2
Fig. 2 Intensity calibrated LIBS emission spectrum of natural uranium metal sample following femtosecond laser ablation in the range of (a) 400 – 500 nm and (b) 500 – 600 nm with a 1.0 μs gate delay and 10 μs gate width averaged over 10 laser shots. After the vacuum chamber was evacuated, it was filled with argon to a pressure of 82 Torr; however, 3 Torr of ambient air leaked into the chamber during the measurement. Strong and commonly referenced uranium emission lines are labeled in the spectrum for neutral (blue), ionic (red), and molecular (black) emissions.
Fig. 3
Fig. 3 Uranium LIBS spectra at 95, 440, and 730 Torr air pressure for several gate delays and widths. The spectra were intensity corrected for a range of ICCD gains used during the measurement. A vertical dashed line has been placed at the center of the observed UO emission line to help guide the eye.
Fig. 4
Fig. 4 Temporally resolved peak intensity of (a) U I 591.53 nm and (b) UO 593.57 nm emission lines with a constant gate width of 1.0 μs. The smooth curves in the figure are the exponential decay fit. The measurements were taken at atmospheric pressure.
Fig. 5
Fig. 5 Temporally resolved molecular-to-atomic emission ratio for the emission lines referenced in Fig. 3 with a constant gate width of 1.0 μs under ambient atmospheric conditions.
Fig. 6
Fig. 6 U I 593.38 nm and UO 593.57 peak emission intensity as a function of the ambient air pressure in the vacuum chamber.

Equations (3)

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U+ O 2 UO+O
UO+ O 2 U O 2 +O
U O 2 + O 2 U O 3 +O

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