Kohno Kenta, Orii Yosuke, Sawada Hisashi, Okuyama Daisuke, Shibuya Kimihiko, Shimizu Seiji, Yoshimura Masashi, Mori Yusuke, Nishimae Junichi, Okada George
Opt Lett. 2020 Apr 15;45(8):2351-2354. doi: 10.1364/OL.389017.
We report the generation of a 266 nm deep ultraviolet (DUV) picosecond pulse with an average output power of 14 W by the fourth-harmonic generation (FHG) from two consecutive frequency-doubling stages of a 1064 nm pulse based on a gain-switched-laser-diode (LD)-seeded hybrid fiber/solid-state master oscillator and power amplifier (MOPA) system. Through the gain-switched operation of a narrow-spectral-linewidth distributed-feedback laser diode and by using a Yb-doped fiber and a two-stage ${\rm Nd}:{{\rm YVO}_4}$Nd:YVO solid-state amplifier, we achieved an average power of 46.5 W near the Fourier transform limit for a 13 ps pulse with a repetition rate of 200 kHz. The narrow linewidth pulse characteristics enabled highly efficient frequency conversion, and the efficiency of conversion from 532 to 266 nm was 54%, and from 1064 to 266 nm was 31%. The beam quality factor ${M^2}$M of the generated DUV pulse was below 1.2. The highly efficient FHG process resulted in appeasing thermal stress caused by nonlinear absorption in the crystal, and more than 5000 h of continuous operation were achieved without any power down or beam profile degradation.
我们报道了基于增益开关激光二极管（LD）种子源的混合光纤/固态主振荡器和功率放大器（MOPA）系统，通过对1064 nm脉冲进行连续两级倍频的四阶谐波产生（FHG），产生了平均输出功率为14 W的266 nm深紫外（DUV）皮秒脉冲。通过窄谱线宽度分布反馈激光二极管的增益开关操作，并使用掺镱光纤和两级Nd:YVO₄固态放大器，我们在重复频率为200 kHz时，实现了13 ps脉冲在傅里叶变换极限附近46.5 W的平均功率。窄线宽脉冲特性实现了高效频率转换，从532 nm到266 nm的转换效率为54%，从1064 nm到266 nm的转换效率为31%。所产生的深紫外脉冲的光束质量因子M²低于1.2。高效的四阶谐波产生过程减轻了晶体中非线性吸收引起的热应力，实现了超过5000小时的连续运行，且没有任何功率下降或光束轮廓劣化。
