We report on the continuous-wave and tunable laser operation of a transparent Yb:YAG ceramic which is prepared by non-aqueous tape casting method with vacuum sintering at 1750 °C for 10 h. The Yb:YAG ceramic is dense and with excellent optical in-line transmittance characteristics. In the lasing experiment, the Yb:YAG is end-pumped by a high-brightness 974 nm diode pump in fiber core of 50 μm and numerical aperture of 0.22, which results in a maximum output power of 7.01 W and a slope efficiency of 60.2% at 1050 nm. A smooth tunable curve from 1022 nm to 1058 nm is achieved in tunable laser testing, revealing the broadband lasing spectra over 30 nm.
© 2015 Optical Society of America
Transparent laser ceramics are the prevailing gain media for high-efficiency, miniature and all-solid-state lasers [1–3]. In recent decades, as there is an increasing demand for high-power, ultra-short pulses near 1.0 μm in many scientific fields like optical atomic clocks, optical imaging, and laser radar, etc, ceramic lasers based on trivalent-ytterbium-ion (Yb3+) doped materials have been enjoying an upsurge of research and investigation [4–7]. As a result, large number of laser media have been fabricated and improved such as Yb: Y3Al5O12 (Yb: YAG), Yb: Y3Sc2Al4O12 (Yb: YSAG), Yb: KY(WO4) (Yb: KYW), etc., and many excellent results have been reported [8–12]. For example, in 2004, the efficient laser oscillation of 72% slope efficiency for input pump power of Yb3+-doped disordered Y3Al5O12/Y3Sc2Al4O12 (YAG/YSAG) ceramics was demonstrated and passively mode-locked laser generating pulses as short as 280 fs with 62 mW average output power at 1035.8 nm was achieved [13, 14].
However, Yb:YAG has always been the most popular gain material for high power diode-pumped solid-state lasers, ultrafast lasers, and widely tunable lasers , because it exhibits the advantages including a wide emission bandwidth, an over 90% high quantum efficiency, a longer upper-state lifetime of:1 ms and a low pump defect that results in the reduction of heat loading. Moreover, it has no undesirable loss processes such as excited-state absorption, up-conversion, and concentration quenching owing to its simple electric structure [16–19]. Considerable efforts have been made to improve the Yb:YAG lasers for efficient and high-power laser performances. In 1997, T. Taira et al. carried out the modeling and experiment results of the longitudinally pumped quasi-three-level Yb:YAG laser oscillators, where their predictions on low threshold and high slope efficiency Yb:YAG lasers was confirmed by a 75% maximum slope efficiency CW lasing operation demonstrated by a Ti:Al2O3 laser pumped, short cavity, Yb:YAG laser . They further investigated the diode-pumped tunable Yb:YAG miniature lasers at room temperature and found out the simple design rule for optimizing end pumping of three- and four-level lasers with respect to the pump intensity and the local threshold intensity, which is of great significance in practical applications . Moreover, by using a double quartz-birefringent filter and an angle tuned LBO in Yb:YAG ceramic microchip laser cavity, a tunable intra-cavity frequency doubling oscillation from 515.3 nm to 537.7 nm was demonstrated, with a maximum green power of 520 mW [22, 23]. Besides, a face-cooled active mirror laser configuration using the thin disc or microchip active medium is feasible for updating lasers designs, concerning the solutions for reducing thermal effects and reabsorption loss. And diode edge pumping is a unique configuration for active mirror lasers due to the possibility of efficient pump absorption in the gain core even with single-pass pumping. The first CW operation up to 90 W of edge-pumped Yb:YAG microchip lasers was demonstrated by using Au–Sn soldering system. The slope efficiency and optical-to-optical efficiency of pump power reached 40% and 28%, respectively .
In addition, in order to enhance ceramic lasers to be of more favorable spectroscopic properties and thermal conductivity, the research interests in ceramic fabricating techniques never decline. In 1995, A. Ikesue et al. developed transparent polycrystalline trivalent rear-earth-ion-doped YAG ceramics using a solid-state reaction (SSR) and vacuum-sintering method [1, 25]. And T. Yanagitani et al. developed a co-precipitation method with vacuum sintering which can produce high quality YAG ceramics [26–30]. The two methods mentioned above are the main techniques for producing YAG ceramics. Accordingly, in 2000, researchers have pointed out a pioneering idea on engineered composite structure of laser ceramics, which not only offers a practical solution to intra-cavity thermal generation, but also makes the fabrication process for ceramic materials simpler and more flexible. It is also beneficial to the commercialization of laser ceramics since lower costs and shorter preparing time are required . Further reports on an efficient laser operation of 340 W CW output power (56 kW/cm3 of output power density) in a hybrid (single-crystal/ceramics) composite YAG edge-pumped microchip laser were published in 2006 , after which a demonstration up to 520 W quasi-continuous-wave and 414 W continuous-wave output power was obtained in a composite all-ceramic Yb:YAG microchip laser. The extracted CW output power density emitted from the ceramic core was 3.9 kW/cm2, and the power density from the active volume was 0.19 MW/cm3. The maximum output power densities are twice that of high-power diode-pumped disk lasers using single-crystal Yb:YAG and these performances are the highest for an active mirror solid-state laser .
On the other hand, tape casting method is an effective way to obtain transparent composite YAG ceramics with gradient structure [33, 34]. In tape casting fabrication technique, the single tape can be controlled at the micro-meter level by adjusting the gap of the blade. According to the solvent used in the slurry system, tape casting is divided into aqueous and non-aqueous tape casting. Although aqueous tape casting is an environmental friendly method as the solvent is harmless water, the non-aqueous tape casting method has shorter production cycle by rapid volatilization of the organic solvents, and the composition can be adjusted by different solvents for preparing different slurry systems. The quality of the tapes prepared by the non-aqueous method is excellent owing to the lower surface tension of the organic solvents compared to water [35–38], which leads to better microstructure and optical properties . Nowadays, rare earth doped YAG ceramics prepared by non-aqueous tape casting method and their related laser performances have been successfully demonstrated [40, 41].
In this paper, we report on the preparing process, the microstructure properties and the continuous-wave laser performance of a transparent 10 at% Yb:YAG ceramic fabricated by non-aqueous tape casting method through sintering a mixture of commercialα-alumina (α-Al2O3), yttria (Y2O3) and yttrerbia (Yb2O3) powders with MgO as sintering additives. In the lasing experiment, we have achieved the continuous-wave lasing in a maximum output power of 7.01 W with a slope efficiency of 60.2% in central wavelength of 1050 nm. In wavelength tuning experiments, a smooth tunable curve from 1022 nm to 1058 nm has been realized by using the intra-cavity SF57 prism under CW operation, revealing the lasing spectra over 30 nm.
2. Experiment results and discussion
To be specific, we employ α-Al2O3, Y2O3 and Yb2O3 powders (Alfa Aesra, USA) as the mixing materials, the absolute ethyl alcohol and xylenes (ACS 98.5%, Alfa Aesar, USA) as the solvents, and the menhaden fish oil (MFO, F8020-500ML, Sigma–Aldrich, USA) as the dispersing agents. In the first procedure, we take on the traditional ball milling to grind the mixture for 12 h, after which polyvinyl butyral (PVB, B-98, Aladdin Chemical Ltd., China) is added into the mixture as the binder. The PEG-400 and butyl benzyl phthalate (BBP, 98%, Alfa Aesar, USA) in mass ratio of 1:1 are also added into the mixture as the plasticizers. These components are further ball milled for another 12–24 h to obtain the slurry with homogeneous compositions. Then, the slurry is de-aired in a vacuum device for 30 min. The height between the blade and the substrate is 500 μm and the casting velocity of the belt is 100 mm per minute. The tape is dried at 25°C for 6 h in the confined space to control the rapid volatilization of the organic solvents, and the dried tape is cut to pieces and laminated for 20–80 layers at 85°C for 30 min under the pressure of 40 MPa. The sintering process is performed at 1750°C for 10 h in a tungsten mesh-heated vacuum furnace (<10−3 Pa, ZW-90-23, Shanghai Chenrong Electric Furnace Co., Ltd., China) . The compositions of the non-aqueous-slurries are presented in Table 1. and the fabrication process of multilayer Yb:YAG ceramics by non-aqueous tape casting is illustrated in Fig. 1.
Figure 2(a) shows the photo of annealed (left) and unannealed (right) Yb:YAG (10 at%) composite ceramic samples, which are completely transparent and without any macroscopic optical defects as observed. We attribute the dark green color in the unannealed ceramic to the co-existence of divalent ytterbium ions (Yb2+) and trivalent ytterbium ions (Yb3+), where the Yb2+ ions absorb the visible light in range of 510-835 nm, as shown in Fig. 2(b). Nevertheless, from the results in Fig. 2(b), the annealed sample has no absorptions in visible region as the annealing process transfers the entire Yb2+ ions to Yb3+ ions. In the UV region, the annealed Yb:YAG ceramic demonstrates one absorption peak at 255 nm which is caused by the light absorption of Fe3+ ions as impurities. And the unannealed Yb:YAG ceramic shows two absorption peaks dominating at 376 nm and 263 nm, which are caused by the optical transitions of Yb2+ ions. Moreover, in spectra range of in ~900 nm to ~1100 nm, the samples exhibit common absorption peaks at 915 nm, 940 nm, and 970 nm, respectively, which correspond to the absorption bands of Yb3+ ions. .
Correspondingly, the in-line transmission curves of the two ceramic samples are depicted in Fig. 2(c). In the visible range, the unannealed sample demonstrates two transmittance concaves that conform to the light absorption peaks. The transmittance ratio at 400 nm of the annealed sample reaches 82.1%. In the near infrared range, the two sample ceramics exhibit representative transmission peaks of Yb3+ ions and their transmittance ratios at 1100 nm are both higher than 83%. Figure 3 shows the SEM morphologies of the Yb:YAG ceramics in 1000 times of magnification, indicating that there exists no pores in the microstructure of the sample. The average size of the Yb:YAG grains is around 18 μm and no secondary phase at the grain boundaries are observed. Based on the descriptions above, we claim that the Yb:YAG ceramics prepared by non-aqueous-based tape casting herein satisfy the standards of laser material.
Subsequently, we employ both the plano–plano laser resonator (Fig. 4(a)) and the three-mirror laser resonator (Fig. 4(b)) to fully investigate the spectroscopic and laser properties of a 10 at% Yb:YAG ceramic sample prepared by non-aqueous-based tape casting method. In both configurations, the laser cavity is designed to reduce the thermal effects which can result in quantum defects of absorbed pump power in the laser medium . To pump this Yb:YAG ceramic, we use a 30 W fiber-coupled high-brightness 974 nm diode laser with an emitting fiber core diameter of 50 μm, numerical aperture of 0.22. Its central output wavelength is stabilized at 974 nm by adopting diode temperature controlling methods. We collimate the pump light using a set of 1:1 lenses, and thereby the emitting pump beam is focused on the laser ceramic with a beam radius of 50μm.
The experimental setups are shown in Fig. 4, a flat dichroic input mirror M1 (anti-reflection-coated: 940–976 nm, high-reflection-coated: 1020–1120 nm), and an output coupler (OC) with optional transmission ratio over 90% in realm of 1020~1120 nm are used in both the cavities. The three-mirror laser resonator possesses a concave output coupling mirror M2 with a curvature of 300 mm (high-reflection-coated: 1020–1120 nm) and a dispersive prism mounted at Brewster’s angle as the wavelength tuning component. The 10 at% Yb:YAG ceramic is vertically cut into the size of 3.9 mm long, 5 × 5 mm2 in aperture with optical polishing surfaces. In the spectroscopic and laser experiments, we coil the four non-light-passing surfaces of the Yb:YAG ceramic with indium foil and install it tightly in a water-cooled copper holder to dissipate the cumulative thermal loads. The corresponding controlled temperature of the gain medium is at 14°C. The cavity lengths of the plano–plano and three-mirror laser resonator are around 30 mm and 370 mm, respectively.
Firstly, we investigate the Yb:YAG ceramic in plano–plano laser cavity with an optical coupler in transmission ratio of 2%. As shown in Fig. 5(a), continues-wave laser operation is achieved at the threshold absorbed pump power of ~1.46 W, and the output power improves linearly with the increment of pump power. Under the absorbed pump power of ~11.76 W, the laser reaches maximum output power of ~2.53 W, corresponding to a slope efficiency of 24.1%. Then, we replace the 2% transmission output coupler in the laser cavity with a T = 5% and a T = 10% coupler to test the ceramic, separately. The laser cavity with T = 5% transmission coupler demonstrates a saturated pump power of ~13.44 W and maximum output power of 4.16 W, corresponding to a slope efficiency of 37.8%, and the cavity with T = 10% transmission coupler demonstrates a saturated pump power of ~15.12 W and maximum output power of 6.89 W, corresponding to a slope efficiency of 58.8%. We also measure the power prosperities of the three-mirror laser cavity using the same transmission ratio couplers. The output power as a function of absorbed pump power is shown in Fig. 5(b). With common ~1.46 W absorbed pump power at threshold, the three-mirror laser in T = 2%, 5%, and 10% output coupler demonstrates saturated pump power of ~11.76 W, ~13.44 W ~15.12 W and maximum output power of ~3.40 W, ~6.69 W, and ~7.01 W, with the slope efficiency of 30.8%, 59.5%, and 60.2%, respectively. From the results above, we can see that in both laser configurations, the maximum output powers and slope efficiencies increase successively when larger transmission ratio output couplers are used. And under the same transmission ratio, the three-mirror laser is more efficient than the plano–plano laser. Moreover, the 10 at% Yb:YAG ceramic exhibits stable lasing properties with respect to pump threshold and saturation powers.
Meanwhile, we measure the output laser wavelength by using a fiber optical spectrum analyzer (Ocean Optics, HR4000) with a resolution of 1 nm. The central emission wavelength of the laser is 1050 nm, as shown in insets of Fig. 5(a) and (b). In practice, we’ve observed laser radiation around both 1030 nm and 1050 nm at low powers, corresponding to the two major emission bands of Yb3+ ion from the lowest levels of 2F5/2 to the highest and secondary levels of 2F7/2 manifold, respectively. However, although the fluorescence intensity at 1030 nm is much larger than that at 1050 nm, the highest output power is obtained at 1050 nm because of the mode competition and re-absorption loss in the quasi-three-level Yb3+ in ceramic.
As the three-mirror laser cavity possesses a more stable configuration in terms of better thermal dissipation and less mechanical disturbs, we have measured its output beam quality in a T = 5% OC by using Spiricon M2-200 laser beam analyzer. Figure 6(a) shows the M2 value of the CW laser at threshold emission, which is 1.125 in the horizontal direction and 1.175 in the vertical direction. We’ve observed a deterioration of the beam quality for high-power laser operation. As shown in Fig. 6(b), the measured M2 value expands to be around 1.231 in the horizontal direction and 1.295 in the vertical direction when maximum output power is reached. As far as we know, the beam distortion is mainly caused by the inhomogeneous change of the refractive index of the Yb:YAG ceramic and diffraction impact under high power pump.
In addition, we’ve done a loss estimation on the Yb:YAG ceramic. We remove the OC in Fig. 4(a) and measure the transmitted light power from the ceramic with the increment of pump power. It is found that under the incident pump power of ~32 W, pump saturation of the ceramic occurs with maximum transmitted power of ~14.6 W. This value can give us a general idea on the absorption losses and reflective losses of the ceramic. Also, as the three-mirror laser cavity indicates more reliable lasing results, we have evaluated the cavity round-trip loss by the sets of slope efficiency for various output coupling transmissions from Fig. 5(b), and the calculated cavity round-trip loss is around 5.7% . These results mean that the ceramic herein has a relatively high loss coefficient. On one hand, it is because the surfaces of the ceramic are uncoated. On the other hand, it is possibly caused by the larger scattering loss at the grain boundaries, since the ceramics with higher ytterbium concentration have smaller grain sizes, i.e., an increased number of the grain boundaries . In order to obtain better laser outputs from the ceramic laser, further improvements of the sample with less intrinsic loss and a more efficient cooling on the gain media is necessary.
In another aspect, previous studies show that compared to crystals, composite laser ceramics normally present higher mode-matching efficiencies between the pump and intra-cavity laser beams due to their higher absorption coefficient, and thus leads to higher lasing slope efficiency. The absorption depths in the ceramics are shorter, resulting in larger mode overlap between the pump and the laser beams in the sample . And according to reference  and , for quasi-four-level laser, the waist size of pump beam should be larger than that of laser cavity mode to obtain a good overlap eﬃciency and maintain the higher pumping intensity to saturate the lower level reabsorption loss. Thus the calculated focused spot size onto the 5 × 5 mm2 ceramic should be larger than 100 μm to obtain more efficient slope efficiency. Based on the analyses, we believe that the ceramic sample herein can realize more remarkable power performances if suitable changes on the focal-length of the imaging lenses are conducted in aim of better mode-matching.
On the other hand, by inserting an intra-cavity prism between the folding mirror and the optical coupler, the wavelength tuning of the laser is realized. We conduct the tuning spectra of the laser comprised of fused silica, SF10, SF14, and SF57, respectively. Figure 7 depicts the tunability of the Yb:YAG lasers, which is demonstrated by a T = 5% transmission output coupler when the above different prisms are used. In general, laser oscillation operates around 1030 nm and 1049 nm, corresponding to two discrete emission bands of the Yb3+ ions. Broader and smoother tuning spectra are achieved by using SF14 and SF57, because they can offer larger angular separations for different wavelengths than fused silica and SF10. The SF57 prism applied in our experiment possesses a refractive index of 1.70 around 1050 nm with a calculated chromatic dispersion value of −0.034 μm−1, and it leads to the widest, continuously-tunable laser output spectra from 1022 nm to 1058 nm. The insufficient tuning range in short-wavelength is mainly caused by the limited high-reflection coating bandwidth from 1020 nm to 1120 nm of the laser cavity mirrors. However, the effective laser output at around 1020 nm indicates that this type of Yb:YAG ceramic has the potential of a large cross-section of emission and relatively small reabsorption loss in the waveband near 1 μm. Therefore, tunable lasing below 1020 nm will be expected if more appropriate laser mirrors or 940 nm off-axis laser diode pumping source are used in the laser system.
In conclusion, tunable continuous-wave laser performance is demonstrated by using a 10 at% Yb:YAG transparent ceramic as the gain medium, which is fabricated by non-aqueous tape casting and vacuum sintering method. In the lasing experiment, we obtain a maximum continuous-wave output power of 7.01 W at 1050 nm under the absorbed pump power of 15.12 W, corresponding to an efficient slope efficiency of 60.2%. In the wavelength tuning experiment, we obtain an optimum smooth tunable curve from 1022 nm to 1058 nm by inserting an intra-cavity SF57 dispersive prism. Mode-locking operation and further power scaling of the Yb:YAG ceramic can be achieved by implementing a more thorough annealing and proper coating to the ceramic sample, and by carrying out a better heat removing and pumping geometry in the laser configuration. We believe that this novel ceramic fabricated by non-aqueous tape casting will become a promising alternative in high-power and ultrafast laser applications.
This work was supported by the National Natural Science Fund (61127014, 50990301&51002172), National Key Project for Basic Research (2011CB808105), and the Key Program of Shanghai Association of Science and Technology (Grant No. 11JC1412400).
References and links
1. A. Ikesue, I. Furusato, and K. Kamata, “Fabrication of polycrystalline transparent YAG ceramics by a solid-state reaction method,” J. Am. Ceram. Soc. 78(1), 225–228 (1995). [CrossRef]
2. Y. Wu, J. Li, Y. Pan, J. Guo, B. Jiang, Y. Xu, and J. Xu, “Diode-pumped Yb:YAG ceramic laser,” J. Am. Ceram. Soc. 90(10), 3334–3337 (2007). [CrossRef]
3. W. Li, Q. Hao, H. Zhai, H. Zeng, W. Lu, G. Zhao, C. Yan, L. Su, and J. Xu, “Low-threshold and continuously tunable Yb: Gd2SiO5 laser,” Appl. Phys. Lett. 89(10), 101125 (2006). [CrossRef]
4. C. Stewen, K. Contag, M. Larionov, A. Giesen, and H. Hügel, “A 1-kW CW thin disc laser,” IEEE J. Sel. Top. Quantum Electron. 6(4), 650–657 (2000). [CrossRef]
5. E. Innerhofer, T. Südmeyer, F. Brunner, R. Häring, A. Aschwanden, R. Paschotta, C. Hönninger, M. Kumkar, and U. Keller, “60-W average power in 810-fs pulses from a thin-disk Yb:YAG laser,” Opt. Lett. 28(5), 367–369 (2003). [CrossRef] [PubMed]
6. J. Saikawa, S. Kurimura, I. Shoji, and T. Taira, “Tunable frequency-doubled Yb:YAG microchip lasers,” Opt. Mater. 19(1), 169–174 (2002). [CrossRef]
8. T. Taira, “Recent advances in crystal optics/Avancées récentes en optique crystalline Ceramic YAG lasers,” C. R. Phys. 8(2), 138–152 (2007). [CrossRef]
9. T. Taira, “RE3+-Ion-Doped YAG Ceramic Lasers,” IEEE J. Sel. Top. Quantum Electron. 13(3), 798–809 (2007). [CrossRef]
10. M. Tsunekane and T. Taira, “High-Power Operation of Diode Edge-Pumped, Glue-Bonded, Composite Yb:Y3Al5O12 Microchip Laser with Ceramic, Undoped YAG Pump Light-Guide,” Jpn. J. Appl. Phys. 44(37), 1164–1167 (2005). [CrossRef]
11. J. Saikawa, Y. Sato, T. Taira, and A. Ikesue, “Absorption, emission spectrum properties, and efficient laser performances of Yb: Y3ScAl4O12 ceramics,” Appl. Phys. Lett. 85(11), 1898–1900 (2004). [CrossRef]
12. P. Klopp, V. Petrov, U. Griebner, V. Nesterenko, V. Nikolov, M. Marinov, M. A. Bursukova, and M. Galan, “Continuous-wave lasing of a stoichiometric Yb laser material: KYb(WO4)2.,” Opt. Lett. 28(5), 322–324 (2003). [CrossRef] [PubMed]
13. J. Saikawa, Y. Sato, T. Taira, and A. Ikesue, “Passive mode locking of a mixed garnet Yb: Y3ScAl4O12 ceramic laser,” Appl. Phys. Lett. 85(24), 5845–5847 (2004). [CrossRef]
14. J. Saikawa, Y. Sato, T. Taira, and A. Ikesue, “Femtosecond Yb3+-doped Y3(Sc0.5Al0.5)2O12 ceramic laser,” Opt. Mater. 29(10), 1283–1288 (2007). [CrossRef]
15. A. Ikesue, T. Kinoshita, K. Kamata, and K. Yoshida, “Fabrication and Optical Properties of High-Performance Polycrystalline Nd:YAG Ceramics for Solid-State Lasers,” J. Am. Ceram. Soc. 78(4), 1033–1040 (1995). [CrossRef]
17. H. Zhou, W. Li, K. Yang, N. Lin, B. Jiang, Y. Pan, and H. Zeng, “Hybrid ultra-short Yb:YAG ceramic master-oscillator high-power fiber amplifier,” Opt. Express 20(S4Suppl 4), A489–A495 (2012). [CrossRef] [PubMed]
21. T. Taira, J. Saikawa, T. Kobayashi, and R. L. Byer, “Diode-Pumped Tunable Yb:YAG Miniature Lasers at Room Temperature: Modeling and Experiment,” IEEE J. Sel. Top. Quantum Electron. 3(1), 100–104 (1997). [CrossRef]
22. J. Saikawa, S. Kurimura, I. Shoji, and T. Taira, “Tunable frequency-doubled Yb:YAG microchip lasers,” Opt. Mater. 19(1), 169–174 (2002). [CrossRef]
23. J. Saikawa, S. Kurimura, N. Pavel, I. Shoji, and T. Taira, “Performance of widely tunable Yb:YAG microchip lasers,” OSA TOPS Adv. Solid-State Lasers. 34, 106–111 (2000).
24. T. Dascalu, N. Pavel, and T. Taira, “90 W continuous-wave diode edge-pumped microchip composite Yb:Y3Al5O12 laser,” Appl. Phys. Lett. 83(20), 4086–4088 (2003). [CrossRef]
25. A. Ikesue, T. Kinoshita, K. Kamata, and K. Yoshida, “Fabrication and optical properties of high performance polycrystalline Nd:YAG ceramics for solid-state lasers,” J. Am. Ceram. Soc. 78(4), 1033–1040 (1995). [CrossRef]
26. J. Lu, J. Song, M. Prabhu, J. Xu, K. Ueda, H. Yagi, T. Yanagitani, and A. Kudryashov, “High-power Nd:Y3Al5O12 ceramic laser,” Jpn. J. Appl. Phys. 39(Part 2, No. 10B), L1048–L1050 (2000). [CrossRef]
27. G. A. Kumar, J. Lu, A. A. Kaminskii, K. Ueda, H. Yagi, T. Yanagitani, and N. V. Unnikrishnan, “Spectroscopic and stimulated emission characteristics of Nd3+ in transparent YAG ceramics,” IEEE J. Quantum Electron. 40, 747–758 (2004).
28. H. Yagi, K. Takaichi, K. Ueda, Y. Yamasaki, T. Yanagitani, and A. A. Kaminskii, “The physical properties of composite YAG ceramics,” Laser Phys. 15, 1338–1344 (2005).
29. J. Lu, H. Yagi, K. Takaichi, T. Uematsu, J. Bisson, Y. Feng, A. Shirakawa, K. Ueda, T. Yanagitani, and A. A. Kaminskii, “110 W ceramic Nd3+:Y3Al5O12 laser,” Appl. Phys. B 79(1), 25–28 (2004). [CrossRef]
30. H. Yagi, T. Yanagitani, K. Takaichi, K. Ueda, and A. A. Kaminskii, “Characterization and laser performances of highly transparent Nd:Y3Al5O12 laser ceramics,” Opt. Mater. 29(10), 1258–1262 (2007). [CrossRef]
32. M. Tsunekane and T. Taira, “High-power operation of diode edge-pumped, composite all-ceramic Yb: Y3Al5O12 microchip laser,” Appl. Phys. Lett. 90(12), 121101 (2007). [CrossRef]
33. A. Ikesue and Y. L. Aung, “Synthesis and Performance of Advanced Ceramic Lasers,” J. Am. Ceram. Soc. 89(6), 1936–1944 (2006). [CrossRef]
34. A. Ikesue and Y. L. Aung, “Ceramic laser materials,” Nat. Photonics 2(12), 721–727 (2008). [CrossRef]
35. Y. Fu, Y. Liu, and S. Hu, “Aqueous tape casting and crystallization behavior of gadolinium-doped ceria,” Ceram. Int. 35(8), 3153–3159 (2009). [CrossRef]
36. D. Hotza and P. Greil, “Review: aqueous tape casting of ceramic powders,” Mater. Sci. Eng. A 202(1-2), 206–217 (1995). [CrossRef]
37. M. Descamps, G. Ringuet, D. Leger, and B. Thierry, “Tape-casting: Relationship between organic constituents and the physical and mechanical properties of tapes,” J. Eur. Ceram. Soc. 15(4), 357–362 (1995). [CrossRef]
38. C. Ye, J. Hao, B. Shen, and J. Zhai, “Large Strain Response in <001> Textured 0.79BNT–0.20BKT–0.01NKN Lead-Free Piezoelectric Ceramics,” J. Am. Ceram. Soc. 95(11), 3577–3581 (2012). [CrossRef]
39. X. Ba, J. Li, Y. Pan, Y. Zeng, H. Kou, W. Liu, J. Liu, L. Wu, and J. Guo, “Comparison of aqueous-and non-aqueous-based tape casting for preparing YAG transparent ceramics,” J. Alloy. Comp. 577, 228–231 (2013). [CrossRef]
40. C. Wang, W. Li, X. Yang, D. Bai, K. Yang, X. Ba, J. Li, Y. Pan, and H. Zeng, “Tape casting of a YAG/Yb:YAG/YAG transparent ceramic for a broadband tunable laser,” High Power Laser Science and Engineering 2, e36 (2014). [CrossRef]
41. K. Yang, X. Ba, J. Li, Y. Pan, and H. Zeng, “Multilayer YAG/Yb:YAG Composite Ceramic Laser,” IEEE J. Sel. Top. Quantum Electron. 21(1), 1602705 (2015). [CrossRef]
42. X. Ba, J. Li, Y. Pan, J. Liu, B. Jiang, W. Liu, H. Kou, and J. Guo, “Optimization of dispersing agents for preparing YAG transparent ceramics,” J. Rare Earths 31(5), 507–511 (2013). [CrossRef]
43. A. J. Bayramian, C. D. Marshall, K. I. Schaffers, and S. A. Payne, “Characterization of Yb3+: Sr5-x Bax (PO4)3F crystals for diode-pumped lasers,” IEEE J. Quantum Electron. 35(4), 665–674 (1999). [CrossRef]
44. I. Shoji, Y. Sato, S. Kurimura, T. Taira, A. Ikesue, and K. Yoshida, “Optical properties and laser characteristics of highly Nd3+-doped Y3Al5O12 ceramics,” Appl. Phys. Lett. 77(7), 939–941 (2000). [CrossRef]