Highly efficient cryogenically-cooled Yb:YAG laser

A MOPA laser system for high pulse energy and high average power has been developed by using a cryogenic Yb:YAG. In the regenerative amplifier with our original TRAM architecture, the high pulse energies of 6.5 and 1.5 mJ were obtained at the repetition rate of 200 Hz and 1 kHz, respectively. An optical efficiency was as high as η_o-o = 9.3% with an excellent beam quality of M ² < 1.1, which ensured that a cryogenic Yb:YAG TRAM had a high thermal strength. The following four pass power amplifier with a cryogenic Yb:YAG rod showed 140 mJ at 100 Hz. Both a high optical efficiency of η_o-o = 30% and a high slope efficiency of η_s = 44% showed that an efficient laser operation could be realized for a power amplification with both a high pulse energy and a high average power by using a cryogenic Yb:YAG.     

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.     

激光二极管泵浦的重复频率大能量低温Yb:YAG激光器设计

为实现重复频率大能量激光输出,基于Yb:YAG激光介质低温下良好的热特性和激光特性,设计了12kW高功率激光二极管(LD)阵列泵浦的V型腔低温Yb:YAG激光器(液氮温度)。对于泵浦耦合系统和散热结构两个关键点,分别使用光线追迹方法和有限元方法进行了分析,提出了楔形真空窗口和低温热管等解决方案。模拟结果表明,该设计的激光器热效应较低,可实现重复频率大能量输出。     

低温Yb:YAG放大器增益与热畸变特性实验研究

为了研究低温条件下Yb:YAG放大器的增益和热特性,搭建了一套液氮冷却的低温放大器,开展了实验研究。测量了不同泵浦强度下的小信号增益以及低温和常温下的介质热致波前畸变。结果表明:低温条件下,可以用更少的泵浦能量得到高于常温的增益;常温下泵浦电流200A、脉冲宽度1200μs的小信号增益为1.59;低温下泵浦电流200A、脉冲宽度400μs的小信号增益为1.82,光光效率显著提高。自发辐射放大(ASE)问题在低温下更加显著,采用短脉冲泵浦有利于降低ASE的影响。低温的热管理效果较常温有显著提高,可以在更高的平均功率下运行。     

Sub-kHz cryogenic Yb:YAG regenerative amplifier by using a total-reflection active mirror

The first pulse operation using a total-reflection active mirror (TRAM) with a cryogenic Yb:YAG/YAG monolithic composite ceramics was demonstrated in a regenerative amplifier scheme. More than 5.0 mJ of output pulse energy was obtained for repetition rates between 10 and 450 Hz. A high energy fluence of 3.5 J/cm² on the active media was realized by separating input and output surfaces of the TRAM.     

Investigation of the Emission Cross-sections and the Spectra of (Cr4+, Yb3+): YAG Crystal

The emission and the lifetime data of Cr, Yb: YAG and Yb: YAG were reported. The effective peak stimulated-emission cross section of chromium and ytterbium-co-doped yttrium-aluminum garnets (Cr, Yb: YAG) has been determined to be 8.98 × 10-20 cm2 at room temperature. The luminescence spectrum of Cr, Yb: YAG is the same as that of Yb: YAG. The luminescence lifetime of Cr, Yb: YAG at room temperature is 0.3 ms (Yb: YAG, 1.48 ms ). The causes of the differences in the fluorescence spectra and the stimulated emission cross-section between Yb: YAG and Cr, Yb: YAG crystals were discussed. Also the potential of Cr, Yb: YAG as a self Q- switched laser crystal was discussed.     

Investigation of the Emission Cross-sections and the Spectra of (Cr~(4 ), Yb~(3 ) ): YAG Crystal

l introductionIn recent years, Cr4 --doped crystals have attracted a great deal of attention aspassive Q--,wit,h.,[l~4]. These Cr4 --dOPed crystals include Cr4 : YAG[l'21 ) Cr4 :GSGG[s], Cr4 : YSO['] etc. They have a large absorption cross section and lOwsaturable intensity at the laser wavelength. In comparison with previously usedsaturable absorbers such as dyes['] and LiF: FZ-- [6] cOlor center crystals, Cr4 -dopedcrystals are more photO--chemically and thermally stable and h…     

Effect of ytterbium concentration on cw Yb:YAG microchip laser performance at ambient temperature – Part II: Theoretical modeling

A theoretical model based on a quasi-four-level system is modified to investigate the effect of Yb concentration on performance of continuous-wave Yb:YAG microchip lasers by taking into account temperature-dependent thermal population distribution, temperature-dependent emission cross-section and concentration-dependent fluorescence lifetime, thermal loading, thermal conductivity, and thermal expansion coefficient. The local temperature rise in Yb:YAG crystal caused by the absorbed pump power plays an important role in the laser performance of Yb:YAG microchip lasers working at ambient temperature without actively cooling the sample. The output wavelengths dependent on output coupling, Yb concentration, and pump power level were analyzed quantitatively. The numerical simulation of Yb:YAG microchip lasers is in good agreement with experimental data. The optimized laser operation for Yb:YAG microchip lasers is proposed by varying the thickness and output coupling for different Yb concentrations. The effect of thermal lens, thermal deformation effect, and saturated inversion population distribution inside the Yb:YAG crystal on performance of heavy-doped Yb:YAG microchip lasers are also addressed. PACS 42.55.Xi; 42.70.Hj; 42.55.Rz     

Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.     

Comparison of spectroscopic properties of Yb:YAP and Yb:YAG crystals

The Yb:YAG and Yb:YAP crystals have been grown by Czochralski method. The absorption spectra and the fluorescence spectra of Yb:YAG and Yb:YAP crystals have been investigated. It is shown that the Yb:YAG crystal has better laser properties and smaller threshold power than Yb:YAP crystal. In addition, the absorption cross-section of the Yb:YAP crystal is 2.16 times of that of the Yb:YAG crystal,so laser diode pumped Yb:YAG lasing can be easily realized. Because YAP single crystal is anisotropic, it is provided with polarization characteristics.     

Laser-diode pumped self-Q-switched microchip lasers

Optical properties of Cr,Yb:YAG, Cr,Nd:YAG crystals, and composite Yb:YAG/Cr:YAG ceramics self-Q-switched solid-state laser materials are presented. The merits of these self-Q-switched laser materials are given and the potentials of such lasers can be chosen by the applications. Cr,Yb:YAG and composite Yb:YAG/Cr:YAG ceramics self-Q-switched laser are conducted. Although several tens of kW peak power can be obtained with a monolithic microchip Cr,Yb:YAG laser, the experimental results show that the performance of this laser is limited by the absorption of Cr⁴⁺ ions at a pump wavelength of 940 nm and strong fluorescence quenching at high Cr concentration. Composite Yb:YAG/Cr:YAG ceramics are more suitable to realize high pulse energy and peak power (up to MW level) with optimized lasing and Q-switching parts. In addition, the instabilities induced by the multi-longitudinal mode competition in Cr,Nd:YAG and Cr,Yb:YAG microchip lasers are addressed. The different gain bandwidths of Yb:YAG and Nd:YAG play an important role in the instability of the output laser pulse trains. Stable laser pulses from the Cr,Yb:YAG microchip laser were obtained due to the antiphase dynamics. For the Cr,Nd:YAG microchip laser, the instability caused by the multi-longitudinal mode competition is an intrinsic property. Different transverse patterns were observed in Cr,Nd:YAG microchip lasers when a pump beam with larger diameter was used. Saturated inversion population distribution inside the gain medium plays an important role in the transverse pattern formation. Different transverse patterns were reconstructed by combining different sets of the Hermite-Gaussian modes.     

Laser-diode pumped heavy-doped Yb:YAG ceramic lasers

Laser performance of heavy-doped Yb:YAG ceramics was investigated using a two-pass pumping miniature laser configuration. Slope efficiency of 52% and optical-to-optical efficiency of 48% have been achieved for 1-mm-thick YAG ceramic doped with 20 at.% ytterbium ions. Laser spectra of Yb:YAG ceramic and single-crystal lasers were addressed under different intracavity laser intensities. Heavy-doped Yb:YAG ceramic is more suitable for a thin disk laser than a single-crystal with the same Yb(3+)-ion lasants.     

Yb:YAG晶体的光谱性能

系统地研究了不同掺杂浓度的Ｙｂ：ＹＡＧ晶体的光谱特性,通过吸收光谱的测量计算了晶体的吸收截面,用对易法计算了晶体的发射截面。在Ｙｂ：ＹＡＧ晶体毛坯中发现Ｙｂ＾２＋和色心,其浓度随Ｙｂ：ＹＡＧ晶体中Ｙｂ＾３＋的增加而增加。经１４００℃氧气氛退火后消失。首次用光子激发和Ｘ射线激发研究了Ｙｂ：ＹＡＧ晶体的荧光特性。     

Study of the effects of Cr ions on Yb in Cr,Yb:YAG crystal

The absorption and fluorescence spectra of Cr,Yb:YAG crystal were measured. There are two absorption bands at 940 nm and 968 nm although the absorption coefficient is lower than that of the absorption peak of Yb:YAG superimposed in Cr:YAG absorption peak. The emission peak intensity is 4 times lower than that of Yb:YAG, which may be caused by the existence of the ground state absorption of Cr⁴⁺ which quenches the Yb³⁺ emission intensity. Although the emission peak of Cr,Yb:YAG is lower than that of Yb:YAG, there is an advantage of this crystal which combines the saturable absorber and gain medium into one and can be a self-Q switching laser crystal if Cr,Yb:YAG crystal is pumped with high energy power.     

不同Yb掺杂量的Yb:Y3Al5O12晶体的光谱分析

采用提拉法生长了Yb³⁺掺杂量分别为5.4at%, 16.3at%, 27.1at%, 53.6at%和100at%的Yb:Y₃Al₅O₁₂晶体.系统地表征和分析了Yb³⁺掺杂量对晶体吸收光谱和荧光光谱的影响.随着Yb³⁺掺杂量的增加，各峰值吸收系数呈线性增加的趋势.应用Smakula公式计算了各吸收峰对应的振荡强度，并分析了Yb³⁺掺杂量对振荡强度的影 关键词： 吸收光谱 荧光光谱 自吸收 浓度猝灭     

YAG晶体中Cr4+和Yb3+的光谱和荧光特性研究

报道了（Ｃｒ＾４＋,Ｙｂ＾３＋）：ＹＡＧ晶体的吸收光谱和荧光光谱特性。在室温下,（Ｃｒ＾４＋,Ｙｂ＾３＋）：ＹＡＧ晶体在９３７ｎｍ和９６８ｎｍ处存在两个吸收带,能与ＩｎＧａＡｓ激光二级管有效耦合：而且在１０３０ｎｍ处有一Ｃｒ＾４＋吸收峰,可以实现对Ｙｂ＾３＋的自调Ｑ激光输出。（Ｃｒ＾＋,Ｙｂ＾３＋）：ＹＡＧ 荧光光谱与Ｙｂ＾３＋：ＹＡＧ晶体一样,发光中心也是位于１０２９ｎｍ,但其强度比Ｙｂ＾３＋：     

Yb：YAG晶体的光谱和激光性能

研究了Ｙｂ：ＹＡＧ晶体的光谱特性,通过不同掺杂深度的Ｙｂ：ＹＡＧ晶体的荧光寿命的测定,确定了Ｙｂ＾３＋在Ｙｂ：ＹＡＧ晶体的最佳掺杂浓度,用合作上转换机制解释了高浓度掺杂时的荧光浓度猝灭效应,研究了掺杂原子分数为０．２的晶体微片的激光性能。     

Thermoexoelectronic and thermoluminescent properties of transparent YAG:Nd and YAG:Yb nanoceramics

Preliminary investigations of thermoluminescent and thermoexoelectronic properties of transparent microstructured YAG:Nd and YAG:Yb ceramics are performed. Five peaks of thermostimulated luminescence are found for YAG:Nd in the VUV and UV ranges. Four and six peaks of thermostimulated exoemission are found for YAG:Yb and YAG:Nd, respectively. The parameters of carrier traps are calculated.     

Demonstration of a compact 100 Hz, 0.1 J, diode-pumped picosecond laser

We have demonstrated an all-diode-pumped Yb:YAG chirped pulse amplification laser that produces 100 mJ pulses of 5 ps duration at 100 Hz repetition rate. The compact laser system combines a room-temperature Yb:YAG regenerative amplifier for increased bandwidth and a cryogenically cooled Yb:YAG four-pass amplifier for improved heat dissipation and increased efficiency. The optical efficiency of this amplifier is higher than that of other diode-pumped systems of comparable energy.     

LD端面泵浦矩形Yb:YAG晶体热效应研究

建立了激光晶体热传导模型。通过求解泊松方程,得到了不同Yb3+离子掺杂浓度的Yb:YAG晶体内温度场分布及由此引起的光程差和热焦距,求出了在不同泵浦半径下的端面温度分布。研究结果表明:随着Yb3+离子掺杂浓度的增加,Yb:YAG晶体端面中心温度升高,晶体中心轴温度衰减加快,热焦距变小;随着泵浦光斑半径的增大,晶体端面中心温度降低。这一结论对改善Yb:YAG晶体热效应提供了理论依据。