Random lasers are a type of lasers that lack typical resonator structures, offering benefits such as easy integration, low cost, and low spatial coherence. These features make them popular for speckle-free imaging and random number generation. However, due to their high threshold and phase instability, the production of picosecond random lasers has still been a challenge. In this work, we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers. Notably, stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 µJ, indicating the gain-switching mechanism. Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value, the number of inversion populations in the “scattering cavity” surpasses the threshold rapidly. Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon. This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.

We present an effective approach to realize a highly efficient, high-power and chirped pulse amplification-free ultrafast ytterbium-doped yttrium aluminum garnet thin-disk regenerative amplifier pumped by a zero-phonon line 969 nm laser diode. The amplifier delivers an output power exceeding 154 W at a pulse repetition rate of 1 MHz with custom-designed 48 pump passes. The exceptional thermal management on the thin disk through high-quality bonding, efficient heat dissipation and a fully locked spectrum collectively contributes to achieving a remarkable optical-to-optical efficiency of 61% and a near-diffraction-limit beam quality with an M² factor of 1.06. To the best of our knowledge, this represents the highest conversion efficiency reported in ultrafast thin-disk regenerative amplifiers. Furthermore, the amplifier operates at room temperature and exhibits exceptional stability, with root mean square stability of less than 0.33%. This study significantly represents advances in the field of laser amplification systems, particularly in terms of efficiency and average power. This advantageous combination of high efficiency and diffraction limitation positions the thin-disk regenerative amplifier as a promising solution for a wide range of scientific and industrial applications.

尽管纹身的人数在增加，但希望祛除纹身的需求量也在增加。现在纹身祛除大多采用激光进行治疗，但仅凭肉眼观察的单次疗效不够理想，往往需要重复治疗。因此，研究了基于图像技术量化评价治疗的效果。使用皮秒激光对猪皮的不同颜色的纹身进行照射，采集治疗部位与正常皮肤组织的图像，再标准化提取部位，并对此部位的图像进行特征提取后，量化照射前后的纹身所占面积比，进而得到祛除率。为了验证量化算法的可靠性，设计了不同对比度的标准图像来计算色素占比，得到的误差均小于0.01%，证明该算法是可靠的。对于色素祛除的量化评价能客观反映激光祛除色素的效果，避免了因医师的主观判断所造成的疗效偏差，为治疗参数的选择及疗效的提高等提供了帮助。

为改善碳化硅的表面润湿性能, 本研究利用脉冲激光加工表面处理和化学改性分别改善了碳化硅的表面形貌和表面能。实验选用皮秒激光加工方式构造表面微织构, 利用激光共聚焦显微镜分析了微织构的微观形貌, 并进一步分析了烧蚀形态与激光自身特性和加工参数之间的联系。研究发现, 激光加工效果以烧蚀为主, 重熔为辅, 而由于碳化硅烧蚀阈值和激光能量在光斑中的高斯分布特性, 形成的微织构的烧蚀凹槽呈倒三角形。此外, 选用的氟硅烷修饰剂使碳化硅表面从亲水表面转变为疏水表面; 通过改变加工参数获得不同微织构并进行氟硅烷修饰后, 碳化硅表面接触角最大提高到157°, 达到了超疏水效果。为了进一步探讨微织构对疏水性的影响原理, 提出了一个基于实际形貌参数的固液接触角模型。该模型阐释了接触角随微织构特征参数变化的机制, 固、气、液两两之间的接触面积影响了表面润湿性, 这为寻找具有最佳疏水性能的微织构提供了新的理论指导。

Multilayer dielectric gratings (MLDGs) are crucial for pulse compression in picosecond–petawatt laser systems. Bulged nodular defects, embedded in coating stacks during multilayer deposition, influence the lithographic process and performance of the final MLDG products. In this study, the integration of nanosecond laser conditioning (NLC) into different manufacturing stages of MLDGs was proposed for the first time on multilayer dielectric films (MLDFs) and final grating products to improve laser-induced damage performance. The results suggest that the remaining nodular ejection pits introduced by the two protocols exhibit a high nanosecond laser damage resistance, which remains stable when the irradiated laser fluence is more than twice the nanosecond-laser-induced damage threshold (nanosecond-LIDT) of the unconditioned MLDGs. Furthermore, the picosecond-LIDT of the nodular ejection pit conditioned on the MLDFs was approximately 40% higher than that of the nodular defects, and the loss of the grating structure surrounding the nodular defects was avoided. Therefore, NLC is an effective strategy for improving the laser damage resistance of MLDGs.

为了提高半导体检测用深紫外激光器的检测效率，需要搭建高功率、高重频257 nm深紫外皮秒激光器实验平台。本文以光子晶体光纤放大器和腔外四倍频结构为基础，进行了257 nm深紫外激光器的实验研究。种子源采用中心波长为1030 nm、脉冲宽度为50 ps的光纤激光器，输出功率为20 mW，重复频率为19.8 MHz。通过两级掺镱双包层（65 μm/275 μm）光子晶体光纤棒放大结构，获得了1030 nm高功率基频光。利用二倍频晶体LBO、四倍频晶体BBO，采用腔外倍频方式获得了257 nm深紫外激光。种子源通过两级光子晶体光纤放大器输出的1030 nm基频光，输出功率为86 W，经过激光聚焦系统后，倍频得到二次谐波515 nm激光输出功率为47.5 W，四次谐波257 nm深紫外激光输出功率为5.2 W，四次谐波转换效率为6.05%。实验结果表明，该结构可获得高功率257 nm深紫外激光输出，为提高半导体检测用激光器的检测效率提供了新思路。