1. Introduction

Since the invention of the first ruby laser in 1960, a range of solid-state lasers is continuously growing. Combinations of ions from the transition-metal group or lanthanides with various matrices resulted in hundreds of laser active materials generating laser radiation covering mainly a visible and near-infrared spectral region. From the point of mid-infrared (mid-IR) spectral region, lanthanides such as Tm³⁺, Ho³⁺, and Er³⁺ enable to generate at certain wavelengths in the ~1.8 to 3 µm wavelength range [1–3]. Active crystals based on transition-metal ion Cr²⁺ in various matrices (ZnSe, ZnS, ZnMgSe, ZnMnSe) were proven to be suitable for tunable laser generation in the 2.2 to 3 µm wavelength range [4–7]. Farther to the mid-IR, Fe²⁺ ion in various matrices (ZnSe, ZnMgSe, ZnMnSe) generating radiation from 3.9 µm up to 5.1 µm were studied [8–18]. Research of lasers extending the possibilities of generating radiation even farther into the mid-IR (5 - 6 µm) is pushed by the lack of compact measuring tools for air pollutant measurements, free-space communications, range-finding, target illumination, molecular spectroscopy, medicine treatment or biomedical diagnostics, and other applications. So far, lasers based on gas (CO laser), semiconductor (lead-salt), lasers using nonlinear effects (as OPO or Raman), or large free-electron laser systems have been used for generation in this wavelength range [2, 19–21]. Even farther to the mid-IR, it should be possible to use the Fe²⁺:Cd_1-xMn_xTe laser. We have already published a paper on the operation at 78 K in the wavelength range 4.95 - 5.27 µm [22–24], and some other results can be found in the literature [25–27].

The aim of this work is detailed study of the spectroscopic and laser characteristics of Fe²⁺:Cd_1-xMn_xTe crystals for a broad content of manganese Mn (x) in a wide temperature range (77-300 K). In comparison with the previously investigated solid-solutions as Zn_1-xMg_xSe or Zn_1-xMn_xSe, the lattice parameter of the Cd_1-xMn_xTe is reported to decrease with increasing Mn content x [28], and some specific behaviour of absorption and fluorescence lines can be expected in this solid-solution.

2. Active media characterization

As active media, a set of Cd_1-xMn_xTe crystals with different cadmium – manganese (Cd – Mn) ratio described by the Mn content x (0.1, 0.52, 0.68, and 0.76) was synthesized using the Bridgman technique. The crystals were doped with Fe²⁺ ions during the synthesis process (iron was added into the initial raw materials in the form of metal powder), and the Fe²⁺ concentration in all cases was on the level of 10¹⁷ cm⁻³. However, further X-ray fluorescence analysis of the synthesized samples has shown higher Fe²⁺ ions concentration, which turned out to be due to additional iron content in manganese raw materials. Thus Fe²⁺ concentration in crystals was growing steadily with Mn (x) content and was evaluated to be 2.1 × 10¹⁸ cm⁻³ (x = 0.1); 2.5 × 10¹⁸ cm⁻³ (x = 0.52); 3.1 × 10¹⁸ cm⁻³ (x = 0.68); 3.7 × 10¹⁸ cm⁻³ (x = 0.76). The investigated samples cross-section was 5 × 5 mm², and the thickness was ~3 mm. The crystal faces were without any antireflection coatings. The spectroscopic properties of this material will be presented in the following paragraphs.

2.1 Fe²⁺:Cd_1-xMn_xTe absorption spectra

The absorption spectra of Fe²⁺ ions in all investigated Cd_1-xMn_xTe crystals within the 2-7 µm spectral range were measured using a FTIR Infralum FT-08 spectrophotometer. The samples were placed in a liquid-nitrogen-cooled temperature-controlled tSTAT335x cryostat from RTI Ltd., and the spectra were measured within a 77-300 K temperature range. Examples of the curves measured for the samples with the Mn content x = 0.1 and 0.68 are shown in Fig. 1. As follows from these graphs, Fe²⁺ ions in the Cd_1-xMn_xTe crystals demonstrate broad absorption spectra covering approximately the region from 1600 cm⁻¹ to 3450 cm⁻¹ (~6250 nm down to 2900 nm) at 300 K; they become narrower mainly in the low-frequency part with the temperature decrease (from ~2500 nm to 5000 nm at 77 K).

 

Fig. 1 Absorption spectra of Fe²⁺:Cd_1-xMn_xTe crystal with Mn content x = 0.1 (a) and x = 0.68 (b) at various temperatures 77 to 300 K.

Download Full Size | PDF

All measured absorption spectra have main maxima around 2700 cm⁻¹ (~3700 nm), and the absorption coefficient is decreasing quite linearly with the temperature increase in all samples - see Fig. 2. Some deviation of the absorption coefficient values for the x = 0.1 sample at low temperature could be caused by low resolution of quite narrow absorption lines at these temperatures (see Fig. 1(a)).

 

Fig. 2 Dependence of absorption coefficient at the absorption maxima of Fe²⁺:Cd_1-xMn_xTe crystal with different Mn content x at various temperatures.

Download Full Size | PDF

The absorption spectra are seen to be not smooth and can be roughly approximated by three Gaussian-shape curves showing important features. Examples of such decomposition are shown in Fig. 3(a)-(c) for x = 0.1 and in Fig. 3(d)-(f) for x = 0.68. The main absorption maximum (central line) and the long-wavelength (low frequency) absorption maxima are shifted towards longer wavelengths with the temperature increase at quite a similar rate in both samples. On the other hand, it can be seen in Fig. 3 that the position of the short-wavelength (high frequency) maxima remains almost unchanged with the temperature increase.

 

Fig. 3 Absorption spectra of Fe:Cd_1-xMn_xTe x = 0.1 (a-c) and 0.68 (d-f) at various temperatures: decomposition into three Gaussian lines (dashed lines). Vertical lines show positions of the main, second (long-wavelength) and third (short-wavelength) absorption maxima.

Download Full Size | PDF

The temperature dependence of the main and long-wavelength absorption maxima positions for these two samples with x = 0.1 and 0.68 are summarized for all measured temperatures in Fig. 4. As follows from this figure, the long-wavelength part of absorption spectra is much more significantly shifted with Mn content (x) increase with respect to main absorption maximum.

 

Fig. 4 Positions of the main absorption spectra maxima (lower lines) and the second, long-wavelength absorption maxima (higher lines) of Fe²⁺:Cd_{1 x}Mn_xTe crystals with low (x = 0.1) and high (x = 0.68) Mn content at various temperatures.

Download Full Size | PDF

Using the estimated Fe²⁺ concentrations in the samples, the 300 K absorption spectra were recalculated into the absorption cross-section spectra for all samples under investigation and the results are shown in Fig. 5(a). As follows from this figure, a minor increase in the absorption cross-section at the absorption maximum (near 3500 nm) is observed with the Mn content increase x being about 0.8 × 10⁻¹⁸ cm² for x = 0.1 and about 1 × 10⁻¹⁸ cm² for x = 0.76. It has to be noted that these changes could occur within the accuracy of the Fe²⁺ concentration determination. The absorption cross-section value of 1 × 10⁻¹⁸ cm² is comparable with Fe²⁺:ZnSe presented in [11], but in Fe²⁺:ZnSe the absorption maximum is at ~3000 nm.

 

Fig. 5 Calculated absorption cross-section (a) and normalized absorption cross-section (b) for Fe²⁺:Cd_1-xMn_xTe crystals with different Mn content x at room temperature. The narrow peaks at ~3430 nm and ~4670 nm are probably caused by nitrogen or some other vapours cooling down the crystal in the cryostat.

Download Full Size | PDF

Figure 5(b) presents the normalized absorption cross-sections. As could be seen from this figure, in the Cd_1-xMn_xTe crystals (unlike in the Zn_1-xMn_xSe [18]) changes in the absorption spectrum shape can be observed in both the short and long-wavelength part of the spectrum. The intensity is changing in the opposite direction, i.e. the short-wavelength line intensity is decreasing with the x increase while at the same time long-wavelength line intensity is increasing with the x increase.

The temperature dependence of the long-wavelength absorption maxima positions for a wide range of Mn content x is shown in Fig. 6. As can be seen from this figure, independently of Mn content x in solid-solution, the long-wavelength maximum is “red” – shifted with temperature at quite a similar rate of about 12 nm per each 10 K.

 

Fig. 6 Temperature dependence of the long-wavelength absorption maxima positions in all Fe:Cd_1-xMn_xTe crystals investigated at various temperatures.

Download Full Size | PDF

2.2 Fe²⁺:Cd_1-xMn_xTe fluorescence spectra

The fluorescence spectra and lifetimes were measured under 4080 nm Fe²⁺:ZnSe laser excitation. This laser was pumped by a flashlamp-pumped Q-switched Er:YAG laser (output wavelength 2940 nm, pulse energy ~15 mJ, pulse duration ~150 ns, repetition rate 1 Hz [29]). The Er:YAG laser radiation was directed without any focusing into the Fe²⁺:ZnSe crystal placed in a LN₂-cooled cryostat equipped by uncoated CaF₂ windows. The Fe:ZnSe laser cavity was placed outside the cryostat and it was formed by a pumping flat dichroic mirror (HT @ 3 µm and HR @ 4 µm) and a concave output coupler (reflectivity R = 95% @ 4 µm; r = 200 mm). The laser was operating at 80 K with the maximum output energy of 3 mJ, pulse duration of ~200 ns (FWHM), and central oscillation wavelength of 4080 nm [14].

The Fe²⁺:ZnSe laser radiation was directed into the examined Fe²⁺:Cd_1-xMn_xTe active crystal placed in another LN₂-cooled cryostat (Janis VPF-100) with uncoated CaF₂ windows.

The fluorescence spectra as well as self-oscillation (without the external cavity) and oscillation (with the external cavity) spectra were measured using a single grating monochromator (Oriel model 77250 with 77301 grating, spectral range 3 – 8 µm) together with a cryogenically cooled MCT photodetector (Judson-Teledyne J15D). The measurements were performed for all samples. The fluorescence spectra for three crystals with Mn contents x of 0.1, 0.52, and 0.68 at three temperatures (80, 200, and 300 K) are shown in Fig. 7 and serve as examples. The spectra were not corrected to the measuring system spectral response.

 

Fig. 7 Temperature dependence of normalized shape of fluorescence spectrum and maximum position for Fe²⁺:Cd_1-xMn_xTe crystals with different Mn content x.

Download Full Size | PDF

As can be seen from this figure, fluorescence spectra maxima measured for all temperatures are shifting towards longer wavelengths with the higher Mn content x increase similar to [22]. However, some specific behaviour of the fluorescence spectra can be observed with the change in temperature. Unlike in the results obtained for Fe²⁺:Zn_1-xMg_xSe or Fe²⁺:Zn_1-xMn_xSe [17,18] where mostly the long-wavelength part of the fluorescence spectrum was significantly changed with the temperature (due to both the “red” shift and intensity changes in the long-wavelength fluorescence line), here we can observe either a more significant change in the short-wavelength part (as can be seen for the sample with low Mn content of 0.1) or changes in both short and long-wavelength parts (for the samples with high Mn content) in the fluorescence spectrum. The detailed Fe²⁺:Cd_1-xMn_xTe fluorescence spectra for Mn content x = 0.1 and 0.68 for low (80 K) and higher (~200 K) temperatures are shown in Fig. 8 and Fig. 9. As follows from these figures the fluorescence spectrum for the crystal with low Mn content x = 0.1 turns from non-symmetrical at 80 K to more symmetrical at about 200 K. On the other hand, the sample with higher Mn content x = 0.68 has quite an opposite tendency (becomes non-symmetrical at about 200 K). To fit the non-symmetrical shape of the fluorescence spectra, a decomposition by two Gaussian-shaped curves was applied. Examples of such decomposition are shown in Fig. 8 and Fig. 9 by the dashed lines. As follows from this decomposition, for the Fe:Cd_1-xMn_xTe crystal with low Mn content the components with higher energy (solid lines in decomposition in Fig. 8 and Fig. 9) have a stronger impact on the fluorescence than for the sample with high Mn content.

 

Fig. 8 Normalized fluorescence spectra of the Fe²⁺:Cd_1-xMn_xTe crystal with low Mn content x = 0.1 with decomposition into two Gaussian lines for: (a) low temperature of 80 K; (b) temperature of 215 K.

Download Full Size | PDF

 

Fig. 9 Normalized fluorescence spectra of the Fe²⁺:Cd_1-xMn_xTe crystal with high Mn content x = 0.68 with decomposition into two Gaussian lines for: (a) low temperature of 80 K; (b) temperature of 200 K.

Download Full Size | PDF

The Gaussian curves maxima positions used for the Fe²⁺:Cd_1-xMn_xTe fluorescence spectra decomposition at different temperatures for two Mn contents x = 0.1 and 0.68 are shown in Fig. 10. Similar to the absorption spectra, the long-wavelength shift of both fluorescence maxima positions is nearly linear with the temperature increase for both Mn contents. The main difference for various Mn content is which spectral line position is more strongly influenced by the temperature. For low Mn content in the Fe²⁺:Cd_1-xMn_xTe solid-solution, the short-wavelength component of the fluorescence spectra is seen to be shifted at much higher rate with the temperature (see Fig. 10(a)) - about 19 nm per 10 K - compared with the long-wavelength component (0.2 nm per 10 K). This is quite opposite to the results for the absorption spectra changes shown above and to the fluorescence spectra changes observed in the Fe²⁺:Zn_1-xMg_xSe and Fe²⁺:Zn_1-xMn_xSe solid-solutions [17,18]. For higher Mn content the short-wavelength component of the fluorescence spectra is shifting more slowly (see Fig. 10(b)) compared with the long-wavelength one (about 0.8 nm compared with 19 nm per 10 K). But, still, this shift is about 4 times more significant than for the sample with low Mn content. The shift of the rapidly changing spectral component in both samples seems to be similar (about 19 nm per 10 K). Both curves for maxima positions of Gaussian components (the lower line in Fig. 10(a) and the upper line in Fig. 10(b)) were found to be in very good agreement with the laser oscillation wavelength maxima measured at corresponding temperatures (red squares in Fig. 10(a) and Fig. 10(b)).

 

Fig. 10 Positions of two Gaussian lines maxima in the fluorescence spectrum decomposition of Fe²⁺:Cd_1-xMn_xTe with Mn content x = 0.1 (a) and x = 0.68 (b) at various temperatures. Red squares mark the positions of oscillation wavelength maxima at corresponding temperatures.

Download Full Size | PDF

2.3 Fe:Cd_1-xMn_xTe fluorescence lifetime

The decay kinetics of Fe²⁺ ions fluorescence was measured for various temperatures and manganese content x in Cd_1-xMn_xTe solid-solution. The experimental arrangement and the instruments were the same as for the fluorescence measurement. Examples of the decay curves at different temperatures (80 – 200 K) for Fe²⁺ ions in Cd_1-xMn_xTe (x = 0.52) crystal are shown in Fig. 11. All decay curves seem to be close to double exponential, with the fluorescence lifetimes increasing with temperature decrease, both in the initial and tail parts. This tendency was similar in all Fe²⁺:Cd_1-xMn_xTe crystals investigated.

 

Fig. 11 Example of Fe²⁺ ions in Cd_1-xMn_xTe x = 0.52 fluorescence decay curves at different temperatures.

Download Full Size | PDF

Temperature dependence of the Fe²⁺ ions fluorescence lifetime (long component) in Cd_1-xMn_xTe crystals with different Mn content x (x = 0.1, 0.52, and 0.68) is shown in Fig. 12. For all samples, the lifetime decreases with temperature increase. This decrease was observed to be more significant for higher Mn contents. At 200 K the lifetimes were 10 μs (x = 0.1) and 2.8 μs (x = 0.68). At 80 K in the same crystals the values were 110 μs (x = 0.1) and 50 μs (x = 0.68).

 

Fig. 12 Temperature dependence of the Fe²⁺ ions fluorescence lifetime (long component) in Cd_1-xMn_xTe crystals with different Mn content x.

Download Full Size | PDF

Decreasing luminescence lifetime at a temperature higher than ~100 K is supposed to be caused mainly by thermally activated nonradiative decay [11]. A single configuration-coordinate model with linear coupling can be considered as a first approximation for the theoretical description of the nonradiative decay. In the case of strong coupling (Huang Rhys factor > 1) and high temperature (kT greater than effective phonon energy) the radiationless transition rate is described by the Mott equation. This process is typical for nonradiative relaxation in optical centers with a strong electron–phonon coupling. This approach leads to a temperature-dependent fluorescence lifetime $\tau (T)$ described by the following equation [31]:

Solid lines in Fig. 12 demonstrate the results of the lifetime temperature dependences fitted for different Mn content x according to Eq. (1). Dependences of these parameters on the Mn content x used in the fit are shown in Fig. 13.

 

Fig. 13 Dependence of radiative lifetime τ_R and energy gap on the Mn content x in Cd1-xMnxTe solid-solution (a). Dependence of non-radiative transition rate WNR on the Mn content x in Cd1-xMnxTe solid-solution (b).

Download Full Size | PDF

As can be seen in these graphs, the radiative lifetime τ_R and energy gap $\Delta E_A$ are decreasing quite linearly with increase in Mn content in the Cd_1-xMn_xTe solid-solution – see Fig. 13(a). At the same time, the non-radiative transition rate W_NR is increasing nearly exponentially with Mn content increase – see Fig. 13(b).

2.4 Fe:Cd_1-xMn_xTe emission cross-section

Using the fluorescence spectra at 80 and 300 K shown above and taking into account the evaluated values of radiative lifetime from the previous section, the emission cross-section was calculated using a standard Füchtbauer-Landenburg equation [11]:

 

Fig. 14 Emission cross section of Fe²⁺:Cd_1-xMn_xTe at 80 K (a) and 300 K (b).

Download Full Size | PDF

3. Fe:Cd_1-xMn_xTe lasing

In the laser experiments, the 4080 nm Fe:ZnSe laser described above was used as a pump source. The radiation was focused by a CaF₂ lens (f = 70 mm) into the investigated Fe:Cd_1-xMn_xTe crystal placed inside the cryostat together with the cavity mirrors. The laser system schematic is shown in Fig. 15. The cavity was formed by a pumping flat dichroic mirror (T ~70% @ 4080 nm and HR @ 5000 – 5800 nm) and a concave output coupler (reflectivity ~99% @5100 – 5500 nm; r = 150 mm). The Fe:ZnSe laser pumping radiation was blocked behind the Fe:CdMnTe laser output coupler, using band-pass filters Thorlabs FB4750-500, FB5250-500, or FB5750-500.

 

Fig. 15 Fe²⁺:Cd_1-xMn_xTe laser system schematic.

Download Full Size | PDF

Lasing was successfully achieved with all the investigated Fe:Cd_1-xMn_xTe crystals within a temperature range from 80 K up to ~240 K. The output energy was measured by a Coherent J-10MB-LE probe and spectral properties were investigated using the Oriel monochromator and MCT photodetector described above. The laser beam spatial profile was monitored by an IR sensitive pyroelectric camera Spiricon Pyrocam III (spectral range 2 – 3000 μm, 124 × 124 pixels). The temporal characteristics were detected by the IR detector Vigo PVI-6 connected to the Tektronix DPO 4104 oscilloscope.

The Fe²⁺:Cd_1-xMn_xTe (x = 0.1, 0.52, and 0.76) laser output characteristics at 80 K are shown in Fig. 16. The absorbed energy was calculated from the absorption coefficient measured by the spectrophotometer (described in Section 2.1). As follows from this figure, the slope efficiency at 80 K with respect to the absorbed energy is growing with Mn content increase. The maximum slope efficiency obtained for the x = 0.76 sample was 0.7%. Relatively low efficiency was probably caused by imperfect crystal faces polishing, non-parallel active crystal faces as well as limited possibilities of the cavity alignment inside the cryostat.

 

Fig. 16 The Fe²⁺:Cd_1-xMn_xTe (x = 0.1, 0.52, and 0.76) laser output energy as a function of absorbed energy at 80 K.

Download Full Size | PDF

An example of the temporal shape of Fe²⁺:Cd_1-xMn_xTe x = 0.52 laser output pulse together with the pumping pulse is shown in Fig. 17. For all crystals, the pulse shape was similar. It can be seen that the Fe²⁺:CdMnTe oscillation pulse started at the maximum of the Fe²⁺:ZnSe pumping pulse and thus it was delayed by about 20 ns from the pumping pulse start. The Fe²⁺:CdMnTe oscillation pulse lasted till the end of the pump pulse and its overall pulse duration was ~800 ns and the leading short pulse duration ~100 ns at FWHM.

 

Fig. 17 Temporal shape of Fe²⁺:Cd_1-xMn_xTe laser output pulse together with the Fe²⁺:ZnSe pumping pulse.

Download Full Size | PDF

The dependence of the Fe:Cd_1-xMn_xTe crystals output energy on temperature and for different Mn content is shown in Fig. 18. It can be seen that the highest output energy (5.7 μJ) was obtained for 80 K for the highest Mn content of 0.76. As follows from this figure, the output energy at low temperature was higher for samples with higher Mn content x (unlike for other solid-solutions like Zn_1-xMg_xSe and Zn_1-xMn_xSe [17, 18]) while the output energy decrease (curves slope) with temperature increase was observed to be more significant for higher x. The overall low output energy is mainly caused by low quality and polishing of the Fe:Cd_1-xMn_xTe crystals as well as limited possibilities of the cavity alignment.

 

Fig. 18 Dependence of output energy of Fe²⁺:Cd_1-xMn_xTe crystals (with different Mn content x) on temperature. Inset: laser output beam spatial profile.

Download Full Size | PDF

The output pulse spatial structure approximately corresponded to the fundamental Gaussian mode, and an example is shown as an inset in Fig. 18. The aberrations were again probably caused by non-parallel active crystal faces as well as limited possibilities of the cavity alignment inside the cryostat.

The measured temperature dependence of the oscillation wavelength for Fe:Cd_1-xMn_xTe crystals with various Mn content x is presented in Fig. 19. A noticeable shift of the central wavelength of oscillation spectra towards longer wavelengths with the Mn content increase was observed to be practically independent of the crystal temperature. The oscillation spectra maxima were ~4950 nm (at 80 K) and 5300 nm (at 240 K) for x = 0.1; ~5130 nm (at 80 K) and 5500 nm (at 220 K) for x = 0.52; ~5300 nm (at 80 K) and 5650 nm (at 240 K) for x = 0.76.

 

Fig. 19 Dependence of the central oscillation wavelength of Fe²⁺:Cd_1-xMn_xTe lasers with different Mn content x on temperature.

Download Full Size | PDF

The oscillation wavelength was observed to increase quite linearly with temperature with a slope of about 19 nm per 10 K following very well the “red” shift of corresponding to the Gaussian components maximum in the temperature dependent decomposition of fluorescence spectra.

4. Conclusions

Spectroscopic properties of Fe²⁺ ions in Cd_1-xMn_xTe solid-solutions in a wide range of Mn content (x = 0.1 – 0.76) were investigated in a broad temperature range of 77 – 300 K for the first time. The absorption spectra at 77 K are ~1500 to 1700 nm broad with a maximum around 3750 nm. With the increasing Mn content as well as temperature, a shift was observed mainly in the long-wavelength spectral part of up to 7000 nm for x = 0.68 at 300 K, while the short-wavelength part remained almost unchanged. The absorption coefficient was generally decreasing with temperature increase, for example in x = 0.52 from 4.4 cm⁻¹ at 77 K to 2.3 cm⁻¹ at 300 K. A minor increase in the absorption cross-section at the absorption maximum was observed with the Mn content increase x being of about 0.8 × 10⁻¹⁸ cm² for x = 0.1 and about 1 × 10⁻¹⁸ cm² for x = 0.76. It has to be noted that these changes could be within the determination accuracy of the Fe²⁺ concentration.

The fluorescence spectra at 80 K were generally ~700 nm broad with the maximum around 5200 nm. With the increasing temperature, the spectrum was getting wider in both the long and short wavelength spectral regions (unlike in Fe²⁺:ZnMgSe or Fe²⁺:ZnMnSe solid-solutions).

Temperature dependence of Fe²⁺ ions lifetime was measured and it shows a relatively slight decrease in lifetime (compared with Fe²⁺:ZnMgSe or Fe²⁺:ZnMnSe solid-solutions) with Mn content increase: from ~110 μs for x = 0.1 to ~50 μs for x = 0.68 at 80 K. Inverse dependence (unlike Fe²⁺:ZnMgSe or Fe²⁺:ZnMnSe solid-solutions) of the non-radiative transition rate W_NR on the Mn content x was observed.

Using the fluorescence spectra measured and lifetime measurements, the emission cross-section was calculated and it was found to increase with the Mn content. This increase was evaluated to be from 2 × 10⁻¹⁸ cm² for x = 0.1 up to 4.5 × 10⁻¹⁸ cm² for x = 0.68 at 80 K.

For the first time lasing in a set of Fe²⁺:Cd_1-xMn_xTe crystals was achieved in a wide temperature range up to 240 K. Output energy up to 5.7 μJ and slope efficiency of 0.7% with respect to the absorbed energy was presented. The central oscillation wavelength can be set by the temperature as well as Mn content in the range from 4950 nm up to 5650 nm.