啁啾脉冲放大激光系统中展宽器色散的解析算法

Analytical algorithem of stretcher dispersion in chirp pulse amplification laser system

时域色散精密控制是超短激光产生及其应用中的关键技术之一,它通过控制各波长的光程产生相对延迟从而改变脉冲宽度.展宽器是啁啾脉冲放大激光系统中对激光脉冲展宽的装置,基于光线追迹法研究光线在展宽器中的传输路径,可计算飞秒脉冲中各波长的光程,进而计算脉冲展宽量并应用于系统设计.由于展宽器的光程表达式复杂,直接对其求导获得色散表达式较困难,目前只能采用数值导数获得近似解,这在计算过程中会引入误差,不利于激光系统精确设计和优化.本文介绍了一种易实现的求解展宽器色散的解析算法,通过归纳展宽器光程表达式特点,引入四个基元函数,将光程表达式分解和反复代换,可得到高阶色散的精确解析值.本文首先对Martinez型展宽器重新光线追迹,获得与Offner型展宽器一致的相位表达式,其次通过解析算法获得了两种展宽器的精确高阶色散值,最后将解析算法与数值算法的结果进行了比较.该解析算法对于啁啾脉冲放大系统的参数设计具有实用价值.

Dispersion control is one of many key techniques in ultrashort laser pulse generation and its applications.By controlling the optical path of wavelength in the laser pulse to generate relative time delay, the pulse width of laser can be changed. The stretcher is the optical scheme to broaden the pulse width in chirp pulse amplification. By using ray trace, the pulse stretch time can be evaluated. However, due to the complicated formula of optical path in stretcher, it is difficult to obtain an analytical expression of high-order dispersion by using direct derivative. In this case, the present numerical methods are commonly used and error would be introduced into the optical system design and optimization inevitably. In this paper we introduce an analytical algorithm of stretcher dispersion. By summarizing the characteristic of stretcher formula, four fundamental functions are introduced to help to calculate the analytical derivative. By substituting the separate terms of the expressions step by step, analytical calculation of stretcher dispersion can be realized. In this paper, the ray trace of Martinez stretcher is first introduced to achieve similar phase expressions to them of existing Offner stretcher, then accurate high order dispersion results are attained by using analytical method, finally the calculation results by using the analytical method and numerical method are compared with each other. The algorithm introduced into this paper for calculating the dispersion is practical and hopeful in designing the chirp pulse amplification laser systems.