A 52-mJ Ho：YAG Master Oscillator and Power Amplifier with Kilohertz Pulse Repetition Frequency

We report on a high energy, high repetition rate Ho：YAG master oscillator and power amplifier （MOPA）, res- onantly dual-end-pumped by Tm：YLF lasers at room temperature. At the pulse repetition frequency of i kHz, we demonstrate a maximum energy of 30mJ per pulse with a 28.2ns pulse width in a Ho：YAG oscillator system resonantly double-end-pumped by Tm：YLF lasers. A maximum energy of 52mJ per pulse with a 30.5ns pulse width is achieved in the Ho： YA G amplifier, corresponding to a peak power of approximately 1.7 MW. The output wavelength is at 2090.6nm and 2096.9nm, and a beam quality factor of M2-2.1 is achieved.     

激光二极管纵向抽运（Tm，Ho）：YLF激光器的研究

对激光二极管端面抽运(Tm，Ho)：YLF固体激光器的激光特性进行了研究。根据激光二极管抽运准三能级系统的特性，详尽地分析了能量在Tm^3 离子和Ho^3 离子之间的传递过程，给出了(Tm，Ho)：YLF激光器准三能级的速率方程，对上转换及激光下能级粒子再吸收对激光二极管抽运(Tm，Ho)：YLF激光器运转的影响进行了理论分析，得出了(Tm，Ho)：YLF激光器的阈值抽运功率和斜率效率的解析表达式。同时对(Tm，Ho)：YLF微片激光器的激光特性进行了实验研究，当保持晶体温度为19℃时，阈值抽运功率为425mW，斜率效率为22．5％，最大光—光转换效率为17．4％，并且在将晶体保持在四个不同的温度下，给出了激光输出功率随抽运功率变化的实验结果。将理论与实验结果进行比较，发现吻合得比较好。     

Performance of a liquid-nitrogen-cooled CW Tm, HorYLF laser

A liquid-nitrogen-cooled Tm, Ho:YLF laser is constructed with a 10-mm-long Tm(6%) and Ho(0.5%) co-doped yttrium lithium fluoride crystal pumped by a laser diode operating at 792 nm. The laser output power is improved by cooling the Tm, Ho:YLF crystal from 300 to 77 K. When the crystal is kept at 77 K, the laser threshold pump power is 230 mW, the slope efficiency is 27.4%, and the maximum optical-to-optical efficiency is 19.9%. At the same time, the relation between the input power and the output power at different temperatures is obtained.     

3.6-W cryogenic Tm,Ho:YLF laser pumped by fiber-coupled diodes module

In this paper, we report a high power cryogenic cooling Tm(6 at.-%),Ho(0.5 at.-%):YLF laser end-pumped by a 19-fiber-coupled-diodes module with the central wavelength of 792 nm at 20°. The highest continuous-wave power of 3.6 W at 2.051 μm is attained under pumping power of 13.6 W, corresponding to optical-optical conversion efficiency of 26%, and the slope efficiency is larger than 30%. The threshold power is only about 0.16 W because of the long lifetime, large effective emission cross section, and low re-absorption in Tm,Ho:YLF crystal.     

LD pumped 2-μm CW laser from Tm,Ho:GdVO_4

A set of fiber-coupled continuous wave (CW) diode lasers has been used to pump Tm, Ho:GdVO_4 and generate 2.048-μm laser radiation at liquid nitrogen temperature. The optical-optical efficiencies of 25%, output power of 3.5 W, and pumping threshold of 838 mW have been obtained and compared with those from Tm, Ho:YLF under identical experimental conditions.     

High Efficiency Continuous-Wave Tm：Ho：GdVO4 Laser Pumped by a Diode

We report a high efficiency cw diode-pumped cryogenic Tin(Sat.%), Ho(0.5at.%):GdV04 laser. The pumping source is a fibre-coupled laser diode with fibre core diameter of 0.4 mm and numerical aperture of 0.3, supplying power 14.8 W at 793.6nm. For input pump power of 13.6 W at 794.2nm, the maximum output power of 4.2 W,optical-to-optical conversion efficiency of 31% and slope efficiency 38% have been attained at 2.0485 μm. To our knowledge, the operating performance is the best among the previously reported Tm:Ho:GdVO4 lasers. We also analyse the influence of pump wavelengths (from 792nm to 794.2nm) on the output power, the optical-to-optical conversion efficiency increases with the longer pump wavelength which is closer to the absorption peak of 797nm in Tm,Ho:GdV04.     

High power 1.57-μm OPO pumped by MOPA with SBS

A Nd:YAG master oscillator power amplifier (MOPA) system, pumped by a pulse flash-lamps as the pump source of optical parametric oscillator (OPO), is employed to improve the pump beam quality of OPO pump source. A back amplifying configuration with stimulated Brillouin scattering (SBS) phase conjugation mirror is used. OPO pump laser energy of 611 mJ/pulse with 30-ns pulse duration is obtained, and near diffraction limited beam quality is achieved. Based on the type Ⅱdegenerate non-critically phase-matched KTP crystal, the OPO is used to convert pump beam from 1.064 μm to 1.57 μm, eye-safe near infrared laser range source. 1.57-μm output energy of 209 mJ/pulse with 18-ns pulse duration is attained with a short cavity KTP OPO, when pump laser energy is approximately 611 mJ. OPO conversion efficiency is up to 38.7% when pump laser energy is approximately 200 mJ.     

二极管泵浦的2 μm高重复频率脉冲固体激光器

 报道了连续二极管端面泵浦2 μm高重复频率Tm,Ho:YLF激光器的实验研究结果。792 nm光纤耦合激光二极管作泵浦源，泵浦液氮制冷的Tm,Ho:YLF晶体。动态运转时，平均输出功率达到4 W，相应的能量抽取效率大于85%。采用声光调Q方式，重复频率1～50 kHz可调，10 kHz时，峰值功率达到12 kW，最小脉宽为32 ns。同时，还对二极管泵浦2 μm激光器设计中的各种因素进行了分析。     

Diode Pumped Operation of Tm,Ho：YVO4 Microchip Laser

A cryogenic and room-temperature diode pumped Tm,Ho：YVO4 microchip laser with 0.5 mm crystal length lasing around 2μm is demonstrated for the first time to our knowledge. Under cryogenic temperature of 77 K, as much as 1.2 W output and slope efficiency of 35% with respect to absorbed pump power are obtained. At temperature of 5℃ the maximum output power of 48mW is obtained at an absorbed pump power of 503 mW, representing a 9.5% optical to optical conversion efficiency. In addition, as much as 8 mW single-frequency output lasing at 2052.6 nm is achieved at room temperature of 15℃.     

Analysis and compensation of thermal lens effects in Tm：YAP lasers

The thermal lens effects in Tm：YAP laser are analyzed by solving the Poisson equation with finite difference method. The thermal focal lengths measured are in the range of 40-90 mm at the pump power of 16-34 W, consistent with the simulation results. The temperature contribution coefficient （the linear coefficient between the maximum temperature in the laser crystal and the pump power） of 1.19 K/W is also obtained. The convex lens and plano-concave mirror thermal lens compensation methods are proposed and applied to a high power pumped Tm：YAP laser.