为了制备高质量表面周期结构，利用法布里-珀罗腔对飞秒激光进行时域整形，输出子脉冲间隔在1~300 ps内灵活可调的飞秒激光脉冲串，在硅表面诱导亚波长周期条纹。实验结果显示，利用飞秒激光脉冲串诱导得到的亚波长周期条纹明显优于原始高斯光诱导的亚波长周期条纹。利用子脉冲间隔为100 ps的脉冲串诱导的亚波长条纹最佳，条纹周期为1 008 nm，结构取向角为2.8°，边缘粗糙度为3.9 nm，可达到光刻工艺的标准。

Parametric interaction allows both forward and backward energy transfers among the three interacting waves. The back-conversion effect is usually detrimental when unidirectional energy transfer is desired. In this theoretical work, we manifest that the back-conversion effect underpins the direct generation of the picosecond pulse train without the need for a laser resonator. The research scenario is an optical parametric amplification (OPA) that consists of a second-order nonlinear medium, a quasi-continuous pump laser and a sinusoidal amplitude-modulated seed signal. The back-conversion of OPA can transfer the modulation peaks (valleys) of the incident signal into output valleys (peaks), which inherently induces spectral sidebands. The generation of each sideband is naturally accompanied with a phase shift of ±π. In the regime of full-back-conversion, the amount and amplitude of the sidebands reach the maximum simultaneously, and their phase constitutes an arithmetic sequence, leading to the production of a picosecond pulse train. The generated picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher, which may facilitate ultrafast applications with ultrahigh speed.

为了改善高能流密度飞秒激光的烧蚀质量，使用法布里珀罗腔产生子脉冲间隔在1~3 500 ps内连续可调的飞秒激光脉冲序列，系统探究了单个飞秒高斯脉冲与不同脉冲间隔的脉冲序列在硅上烧蚀的孔型质量。实验结果显示，子脉冲间隔在50~100 ps范围内时，孔边缘的冠状重熔物大大减少，其厚度仅为单个飞秒高斯脉冲的40%，周围基底几乎没有粘连的粉尘或热损伤痕迹，孔型品质因子数值从单个飞秒脉冲的0.52提升至0.89。本文报道的飞秒激光脉冲序列，基于后续子脉冲与喷出物的二次烧蚀原理，子脉冲间隔在50~100 ps范围内时，后续子脉冲能够最大程度的雾化喷出物，从而减少冠状重熔物与高温粉尘污染损伤，烧蚀质量得到改善。