抑制调Q不稳定性的非线性镜锁模激光器  

Nonlinear Mirror Mode⁃Locked Laser for Suppressing Q⁃Switching Instability

作　　者：韩佳坤 李国泰 李帅[1] 赵静[1] 朱占达[1,2,3,4] 雷訇 李强[1,2,3,4] Han Jiakun;Li Guotai;Li Shuai;Zhao Jing;Zhu Zhanda;Lei Hong;Li Qiang(Faculty of Physics and Optoelectronic Engineering Beijing University of Technology,Beijing 100124,China;Beijing Engineering Research Center of Laser Technology,Beijing 100124,China;Beijing Colleges and Universities Engineering Research Center of Advanced Laser Manufacturing,Beijing 100124,China;Key Laboratory of TransScale Laser Manufacturing Technology,Ministry of Education,Beijing 100124,China)

机构地区：[1]北京工业大学物理与光电工程学院,北京100124 [2]北京市激光应用技术工程技术研究中心,北京100124 [3]激光先进制造北京市高等学校工程研究中心,北京100124 [4]跨尺度激光成型制造技术教育部重点实验室,北京100124

出　　处：《中国激光》2024年第14期46-53,共8页Chinese Journal of Lasers

基　　金：国家自然科学基金(62075003,62275007);北京市自然科学基金(4202007,KZ202110005010)。

摘　　要：为了抑制高功率非线性镜锁模激光器的调Q不稳定性,提出了一种双晶体二次倍频非线性镜结构,通过加入第二块非线性晶体将二次谐波倍频为四次谐波来产生损耗,从而实现非线性反射率的提前饱和。该结构降低了非线性镜锁模器件的饱和峰值功率密度和调制深度,从而降低连续锁模阈值,得到稳定的连续锁模输出。通过理论分析这种非线性镜结构抑制调Q不稳定性的原理和表达,并使用大芯径晶体方波导作为增益介质,进一步搭建实验,验证了这一结构的可行性。最终实验获得了功率为26.5 W、重复频率为32.2 MHz、脉宽为0.95 ps的连续锁模脉冲输出。实验结果表明,这种高功率非线性镜锁模激光器结构简单、稳定可靠,并且该器件在高功率锁模激光器的发展中具有巨大潜力。Objective High-power ultrashort-pulse lasers operating in the picosecond and femtosecond time domains have important applications in strong-field physics, biomedical imaging, optical frequency conversion, and nuclear laser fusion. The direct output of mode-locked lasers has a more promising signal-to-noise ratio, beam quality, and stability than the power amplification method for high-power ultrashort pulse generation. Commonly used mode-locking methods for high-power mode-locked lasers include semiconductor saturable absorber mirror mode-locking(SESAM), Kerr lens mode-locking(KLM), and non-linear mirror modelocking(NLM). In particular, the NLM mode-locking method, which utilizes a nonlinear crystal and an output coupling mirror, has demonstrated significant potential owing to its high stability, wide range of applicable wavelengths, and large modulation depth.However, achieving saturation in the NLM method requires a high power density, resulting in a peak power density within the cavity that is typically lower than that required for reflectivity saturation. The quality factor(Q) of a cavity in an NLM mode-locked laser increases with the peak power density within the cavity. This phenomenon results in Q-switching instability, making it challenging to attain stable continuous-wave mode-locking(CWML). This challenge can be addressed by introducing an early saturation tendency for the nonlinear reflectivity of NLM devices. This ensures a balance between gain and loss at the saturation point, ultimately achieving stable continuous-wave mode-locked pulses. Hence, the development of a straightforward, stable, and dependable method to achieve early saturation is important for achieving high-power mode-locked outputs.Methods In this paper, we present a novel NLM structure involving two crystals that undergo frequency doubling twice. This design introduces loss by incorporating a crystal that doubles the second harmonic, achieving early saturation of reflectivity to effectively suppress Q-switching instability and facili

关 键 词：锁模 晶体波导 调Q 锁模 连续锁模 非线性镜锁模 高功率 

分 类 号：TN248.1[电子电信—物理电子学]