光学参量啁啾脉冲放大中时间抖动对飞秒脉冲对比度的影响

Influences of synchronization time jitter in OPCPA system on contrast ratio of femto-second pulse

基于宽带脉冲的计算模型,采用4阶龙格-库塔法研究了光学参量放大所满足的三光波耦合方程。数值结果表明:时间不同步导致大量本底能量不能被压缩,使本底形成,导致飞秒脉冲展宽,如抖动从0变化到150 ps,则其预脉冲宽度由0.2 ps展宽到0.7 ps,降低了输出飞秒激光对比度,并导致输出能量稳定性降低。采用长而平滑泵浦光脉冲、选择适当长度的非线性晶体、并使系统工作于增益饱和区,能实现高对比度和高稳定的飞秒激光输出。

Based on the propagation model for the wideband ultra-short pulse, the coupled equations which determine the interaction process among pump, idle and signal pulses in the LBO crystal are studied by the fourth-order Runge-Kutta methods. The simulation results are as follows： the synchronization time jitter induces the pedestal generation, which possesses plentiful energy and can not be removed in the compression stage, therefore, the pulse duration stretches and the contrast ratio of the femtosecond pulses decreases seriously, for example, the prepulse stretches from 0.2 ps to 0.7 ps when the synchronization time jitter changed from 0 to 150 ps; Using the longer duration and smoother shape pump pulse can restrain the time jitter effectively, and choosing suitable length of the nonlinear crystal, the femto-second pulse with high contrast and high gain stability can be obtained when the OPCPA system is operating in the saturation region.