Objective High-energy, high-peak power, picosecond pulse lasers have broad application prospects in laser science research and industrial processing. The configuration of a master oscillator power amplifier (MOPA) is commonly used to obtain a high output power. In this case, a low-power oscillator with the desired characteristics is used as the seeder, whose radiation is injected into an amplifier to scale the output power or pulse energy, while other properties remain mostly unchanged. The planar waveguide can provide high seed light injection powers and high pumping power densities. Therefore, the planar waveguide lasers are a potential laser technology for obtaining picosecond pulse laser with high energy and high peak power. Methods A Nd:YAG planar waveguide picosecond laser amplifier is designed. The seed is a fiber picosecond laser, which is amplified by a compactness amplifier with a Nd:YAG planar waveguide as the gain medium to obtain a picosecond laser output. The small signal gain coefficient and power distributions at different positions within the planar waveguide are calculated using related theories. Finally, based on the results of theoretical calculations, a picosecond laser amplifier is designed and built, and the experiment is completed under different seed laser repetition frequencies. Results and Discussions To evaluate the amplification ability of the amplification system under different seed laser repetition frequencies, the seed source is operated at repetition frequencies of 24. 46 MHz, 4. 89 MHz, 2. 038 MHz, 1. 019 MHz, 500 kHz, 200 kHz, 99. 4 kHz, 49 kHz, and 25 kHz, and the output power is obtained as a function of the pump power (Fig. 7 and Table 1). Once the seed light passes through the isolator and the beam expansion system, the single pulse energy injected into the slab is 19. 6 nJ. In the single-end pumped case, when the repetition frequency of the seed source is 24. 46 MHz, the output power is 228 W, the single-pulse energy is 9. 3 mu J, the optical-optical conversion efficiency is 20. 2%, and the beam quality (M-2) values in the guided and non-guided directions are 1. 4 and 4. 6, respectively. In order to measure the amplification system, we change the repetition frequency of the seed laser under the condition that the pulse width of the seed laser is 11. 7 ps and the single pulse energy of the seed laser is fixed at 19. 6 nJ. When the repetition frequency of the seed source is 49. 8 kHz, a laser output power of 31. 6 W is obtained with the single-pulse energy of 0. 63 mJ. When the repetition frequency of the seed source is 25 kHz, a laser output power of 24. 2 W is obtained with the single-pulse energy of 0. 97 mJ and the peak power of 82. 9 MW. The magnification factor is up to 4. 9x10(4). Experimental results show that this amplifier can suppress the amplification of the spontaneous emission (ASE) effect and can effectively increase the magnification, thereby improving the output power and conversion efficiency. Moreover, the method of improving the output and suppressing the ASE is further analyzed based on the theoretical calculations. Experimental results reveal that the system has a strong amplification ability. Conclusions In this study, a back end-pumped Nd:YAG planar waveguide picosecond laser amplifier is designed. The fiber laser provides a picosecond seed source with a tunable repetition frequency, and the pumping source operates in the continuous mode. Based on the results, when the seed light repetition frequency is 24. 46 MHz, the pulse width is 11. 7 ps, the injection power is 0. 48 W, the output power is 228 W, the single-pulse energy is 9. 3 mu J, and the optical-optical conversion efficiency reaches 20. 2%. Moreover, the beam quality values in the guided and non-guided directions are 1. 4 and 4. 6, respectively. In contrast, when the repetition frequency of the seed laser is reduced to 25 kHz, the average output power is 24. 2 W, the single-pulse energy is increased to 0. 97 mJ, and the single-pulse energy magnification factor is 4. 9x10(4), indicating that the amplification system has a strong amplifying ability. The methods to further improve the optical-optical conversion efficiency and suppress ASE are analyzed based on the theoretical calculations. To the best of our knowledge, this is the first report on a planar waveguide picosecond laser amplifier.

高能激光广泛应用于材料加工、科学研究、空间碎片清除、军事应用等领域.二极管泵浦高能激光具有结构紧凑,系统简单、全电驱无限弹仓的特点,近年来,各类二极管泵浦高能激光围绕着同时实现高功率、高效率、高光束质量这一总目标发展迅速.详细综述了国内外高平均功率块状固体激光、高功率可见光波段激光、高峰值功率激光、高功率光纤激光、碱金属蒸气激光等二极管泵浦高能激光的研究进展,并对其发展趋势进行了展望.

This paper presents the research progress of high efficiency and compact all-solid-state lasers based on Yb:YAG slab at room temperature. The laser dynamics model of Yb slab at room temperature is established. It is quantitatively analysed that the pumped laser intensity and the injected laser brightness influence the optical conversion efficiency. The method to suppress the slab-edge-effect is founded. The output power of 22.3 kW, the optical conversion efficiency of 36%, and the beam quality of 2.4 times diffraction limit, were achieved in experiment. These results lay a foundation for the key technology research of higher power laser and development of the miniaturized, lightweight and practical high power Yb slab laser.

A diode pump high power and high efficiency NdYAG planar waveguide oscillator at quasi-continuous mode is reported.The 1mm×10mm×60mm planer waveguide is selected as gain medium.The plane-plane cavity is built, and the output properties of the planar waveguide laser under different output mirror transmissions and different pulse repetition rates are studied.Experimental results show that when the output coupler transmission is 79％, an average output power of 441 Wfor the 1064nm laser is achieved under the pulse repetition rate of 500Hz and the drive current of 200A.Under five different repetition rates, the maximum single pulse energy is 928 mJ, and the effective optical to optical efficiency is 53.2％.The pulse waveform of output laser is consistent with that of the pump laser, and both have a pulse width of 240μs.The output power of the oscillator can be increased after the system optimization.

The depolarization feature in high power,end-pumped Nd∶YAG slab lasers is studied.The polarization control and depolarization compensation in high power slab laser output are realized with the usage of high power polarizer and 90° quartz rotator,which effectively improves the polarized output power and the uniformity of the near-field light intensity distribution.The experimental results indicate that,via the optimization of depolarization compensation,the output power of linearly polarized laser is increased from 8.7 kW to 9.6 kW,and the depolarization rate is decreased from 30.8％ to 3.1％.

Taking Nd∶YAG planar waveguide as gain medium of a laser amplifier,we study the factors affecting optical-optical efficiency of laser with wavelength of 1064 nm during amplification.A free operational Nd∶ YAG rod oscillator with wavelength of 1064 nm is used as seed source,and a diode laser array with wavelength of 808 nm is used as the pump source.The pulse width of pump beam is equal to that of seed,and the output of pump beam and seed is synchronous.The size of the Nd∶ YAG planar waveguide is 60 mm× 10 mm× 1 mm,and the core thickness is 100 μm.The effects of seed energy,pump energy,and pump direction on the laser amplification efficiency are studied.The results show that when the input seed energy is 10 mJ,the quasi-continued laser with maximum energy of 713 mJ is obtained at the pulse repetition frequency of 100 Hz,the pump pulse energy is 1478 mJ,and the corresponding optical-optical efficiency is 47.6％.

开展了高功率双掺杂浓度板条激光技术的理论与实验研究,通过分段掺杂有效降低了板条长度方向上的吸收抽运功率密度的不均匀性,显著提高了单个激光板条的平均储能密度,总储能提高了39%。当二极管总抽运功率为15kW时,3kW的种子光源通过双掺杂板条可提取5.16kW的功率,这个数值相比单掺杂板条增加了36%,且光光转换效率为34.4%,与理论预期基本相符。

设计了一种高效率、结构紧凑的高功率激光放大器。采用解析方法分析了对称结构Nd:YAG双包层平面波导增益介质的内部热应力,获得了其可承受的最大抽运光强。针对不同厚度的内包层结构,采用Trace Pro软件模拟分析得到了最佳的抽运源结构和耦合系统。为了便于进行激光模式控制,掺杂区厚度取为100μm。内包层和外包层分别为纯YAG和蓝宝石,整个波导尺寸为60 mm×10 mm×2 mm。半导体激光器阵列输出的抽运光从波导的两个端面进入,两个大面和铜热沉焊接来获得良好的散热条件。种子光从一个端面注入,单通放大输出。通过模拟计算,在3384 W的抽运功率下,进入波导芯层的种子光功率为0.1 W,放大输出功率可以到达1322 W,光光效率约为39%。

利用端抽运板条放大器多角度通光的特点,建立了一套板条放大器各特性参数的测试系统,实现了动态加载条件下板条放大器的可提取功率、波前畸变及退偏度等多参数的同步测试。该系统包含千瓦级的窄线宽注入光源及提取功率测试系统,高精度热致波前畸变及退偏测试系统。当注入光源功率为2.7 k W,抽运电流为90 A时,板条放大器中可提取功率约为2.9 k W,波前畸变幅值差值小于1μm（27 mm口径）,热致退偏约为5.1%。对比无注入光时测得的放大器相关特性参数,两者差异较大,说明了该测试系统对于准确掌握板条放大器性能的必要性。