实验研究了激光脉冲宽度和脉冲个数对镍基高温合金材料去除阈值的影响，分别在290 fs，1 ps和7 ps脉宽的激光下，使用1，10，50，100，300，500和1000个不同能量的激光脉冲辐照高温合金样品表面。实验结果表明，烧蚀坑尺寸会随脉冲数的增加而增加，而脉冲宽度的增加会加大脉冲个数对烧蚀坑直径的影响。通过烧蚀坑直径的平方值与激光脉冲能量之间存在的对数关系，得到了不同脉冲宽度下镍基高温合金的多脉冲材料阈值。3种不同脉宽下的高温合金多脉冲去除阈值都存在显著的累积效应。根据去除阈值计算得到290 fs，1 ps和7 ps脉宽下的累积效应系数分别为0.88，0.86和0.78。

Non-mode-selective (NMS) multiplexers (muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile (wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion (MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian (HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of -1.6dB, mode-dependent loss of 4.7 dB, and average total mode crosstalk of -4.4dB. Additionally, this design, featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

We propose a mode demultiplexing hybrid (MDH) that integrates mode demultiplexing, local oscillator power splitting, and optical 90-deg mixing using multi-plane light conversion (MPLC). We demonstrate the realization of a three-mode MDH using four phase plates, one more than what is required for an MPLC-based mode demultiplexer, via numerical simulations. The performance of the three-mode MDH is comparable to that of commercial single-mode 90-deg hybrids. This multiple-functionality device enables simplification of the coherent optical front end of mode-division multiplexing receivers.

The spectral purity of fiber lasers has become a critical issue in both optical sensing and communication fields. As a result of ultra-narrow intrinsic linewidth, stimulated thermal Rayleigh scattering (STRS) has presented special potential to compress the linewidth of fiber lasers. To suppress stimulated Brillouin scattering (SBS), the most dominant disturbance for STRS in optical fibers, a semi-quantitative estimation has been established to illuminate the mechanism of suppressing SBS in a periodic tapered fiber, and it agrees with experimental results. Finally, a linewidth compression device based on STRS is integrated into a single-longitudinal-mode ring-cavity fiber laser with secondary cavities, and its linewidth is verified to be 200 Hz through a self-heterodyne detecting and Voigt fitting method.