相干极紫外超连续光谱产生机制和方法的研究

Attosecond optical pulses require eXtreme Ultraviolet (XUV) supercontinuum. Amplitude gating was the first experimental method for XUV supercontinuum and isolated attosecond pulse generation, which has produced pulses as short as 80as. Unfortunately, the supercontinuous spectra generated by amplitude gating were always restricted by the bandwidth of multilayer mirrors employed in the relevant experiments. An attosecond pulse composed by the intrinsic supercontinuum produced by amplitude gating has not been reported. Therefore, it is necessary to investigate the optimal experimental conditions of supercontinuum generation by amplitude gating without the bandwidth limitation of multilayer mirrors. In the proposed project, we plan to measure and optimize the bandwidth and strength of the intrinsic supercontinuum produced by amplitude gating in order to increase the cutoff energy to about 200eV, and to measure the attosecond pulse width of the supercontinuum as well. Similar research has not been reported before. We hope to obtain a bandwidth and pulse length exceeding the best results reported in China. The project is aiming to push forward future research to generate broader spectrum and shorter attosecond pulse. The application of such attosecond pulses promises to offer a formidable tool for a broad range of research and investigation.

相干极紫外（XUV）超连续光谱的产生是获得阿秒脉冲的一个关键前提条件。振幅选通是第一种在实验中产生XUV超连续和单阿秒脉冲的方法，曾获得80as的超短光脉冲。但是，所有利用振幅选通产生的超连续谱都受限于镀膜反射镜的带宽，到目前为止没有利用所产生的XUV超连续全部光谱合成脉冲并测量脉宽的实验结果。因此有必要在实验中去除镀膜镜对光谱的限制而对振幅选通产生的本征XUV超连续及其最佳实验条件进行详细的研究。本项目拟对振幅选通方法产生的本征超连续进行实验观测并充分优化其宽度和强度，争取将截止能量提高至200eV附近，并利用阿秒条纹相机测量脉冲宽度。本项目力争填补国内外对振幅选通方法产生的本征XUV超连续谱研究的空白，可望在光谱宽度和脉冲宽度上突破国内最好结果，也为下一步产生更短的阿秒脉冲获得有指导意义的实验参数。提高光谱宽度可以将阿秒脉冲这一前沿工具推广到更广泛的应用领域，与更多的研究方向交叉结合。

根据项目的任务和要求，项目组利用固体薄片组实现了飞秒脉冲的非线性光谱展宽至一个倍频程，经啁啾镜压缩获得5fs左右的少周期脉冲，取得了国际先进的成果，并已成为实验室中的主要阿秒脉冲驱动光源，实现了载波包络相位（CEP）的锁定和自差频（DFG）的产生和测量；并成功实现阿秒脉冲串的产生和测量。同时利用相干合成光源驱动产生高次谐波，在实验中观察到光谱范围覆盖50到65eV的阿秒超连续。本项目还发展了阿秒条纹相机能谱图反演计算的新方法，初步结果显示此方法计算速度快、准确度高，已成为本课题组内部阿秒脉冲反演的标准方法。项目组取得的这些研究成果为下一步产生和测量更短阿秒脉冲在实验和理论上打下了坚实的基础，提高了在阿秒光学领域的研究水平，并促进了与国内外其他相关研究单位的合作与交流。