泵浦光波形和脉宽对飞秒激光对比度的影响

采用宽带数值模型，应用四阶龙格-库塔数值算法对三波耦合方程进行数值分析，研究了泵浦光的波形和脉宽在提高光参量啁啾脉冲放大系统输出飞秒激光对比度的作用。结果表明：在泵浦光脉宽较小的条件下，采用平滑的泵浦光波形更有利于提高飞秒激光对比度；在泵浦光脉宽较宽时，飞秒激光对比度得到很好地提高，而对泵浦光波形不敏感；但继续提高泵浦光脉宽并不能进一步改善飞秒激光对比度，而系统的转换效率却显著降低。

Improving contrast ratio of compressed pulses in OPCPA system by using long duration pump pulses

The fourth order Runge-algorithm was used in the numerical simulation methods to study the influences of the profiles and durations of pump pulse on the compressed pulses. The LBO crystal was used for the nonlinear gain medium in the numerical simulation. When the narrower duration pump pulses were used, a higher contrast ratio of femtosecond was obtained by adopting the more smooth profiles of the pumps (namely the lower order parameters of pump pulses). The contrast ratio of the femtosecond can be improved by longer duration pump pulse. But the contrast ratio can not be further improved by improving the duration pump pulses further, while much lower conversion coefficient in OPCPA system occurs.