高重频硬X射线自由电子激光脉冲到达时间诊断方法研究

Arrival time diagnosis method of high refrequency hard X-ray free electron laser

X射线自由电子激光(XFEL)脉冲时间诊断技术常用于实验站附近XFEL脉冲和配套激光的相对到达时间探测,是飞秒级XFEL泵浦探测实验的重要辅助技术,为XFEL和激光泵浦探测实验中两种脉冲对准提供参考信号.随着XFEL向高重频、短脉冲发展,对时间诊断中的诊断频率、泵浦样品和分辨率提出了更高的要求.该技术通过泵浦探测和光学互相关实现,当XFEL脉冲入射高带宽半导体样品瞬间,导致样品复折射率突变,使XFEL到达时间编码于突变空间.本文基于空间编码和光谱编码两种方法,研发设计了XFEL单脉冲到达时间诊断装置;并通过Beer’s吸收理论和原子散射理论对X射线与样品作用过程进行模拟,研究了该过程中X射线吸收与折射率突变的响应程度,完善了样品的分析选择模型;对光谱编码中的啁啾脉冲调制进行分析,得到色散介质和脉冲本征参数对诊断分辨率的影响.该研究对XFEL脉冲到达时间诊断装置的应用具有指导意义.

X-ray free electron laser(XFEL)pulse time diagnosis technology is often used to detect the relative arrival time of XFEL pulse and auxiliary laser near the experimental station.It is an important auxiliary technology and provides a reference signal for the pump-probe pulse in the XFEL laser pump-probe experiment.With the development of XFEL towards high repetition frequency and short pulse,higher requirements are put forward for diagnostic frequency,pump sample and resolution in time diagnosis.The technology is realized by the pump-probe method and optical cross-correlation method.When the XFEL pulse is incident on the high-bandwidth semiconductor solid target instantaneously,the complex refractive index of the solid target will change,then the arrival time of XFEL will be encoded in the mutation space.In thiswork,we design an XFEL pulse arrival time diagnostic device based on two methods:spatial coding and spectral coding.In this framework,the interaction between X-ray and solid target is explored by Beer's absorption theory and atomic scattering theory.Therefore,the response to X-ray absorption and refractive index in this process are investigated,and the solid target selection model is developed.This model is used to analyze the influence of solid target type and thickness in diagnosis,while avoiding situations where the sample is too hot due to a lot X-ray absorption.Moreover,the influence of hard X-ray on sample temperature at high frequency is considered,and the samples suitable for different X-ray bands are given.The chirped pulse modulation in spectral coding is analyzed,and the influence of dispersion medium and pulse parameters on the diagnostic resolution of spectral coding are obtained.Finally,the error effects of X-ray,spatial coding and spectral coding on the results are analyzed,and the analysis methods and consideration factors of the two coding methods are given.This work is of great significance in using the XFEL pulse arrival time diagnostic device.