大信号增益区的宽带OPCPA系统特性分析

Characteristics of wideband OPCPA lasers in saturated amplification case

利用大啁啾信号光脉冲的光谱在时域内的分布特点,采用四阶龙格-库塔算法对宽光谱的光参量啁啾脉冲放大(OPCPA)激光器特性进行了数值分析。以LBO晶体为增益介质,信号光脉冲宽度取100 ps、啁啾系数为1000,中心波长为800 nm;泵浦光的中心波长为532 nm,脉宽为100 ps。数值计算结果表明:信号光的非线性相位变化的中心部分为线性分布区,且随增益饱和的程度增大而增大;系统的功率转换效率有准振荡结构,且其第一个极值点为系统能量最大的转换率点;随着系统进入增益饱和区,压缩光脉冲的对比度明显降低,预脉冲长度显著增大。

The spectrum of the signal pulses with big chirped coefficient distrusts linearly around the central wavelength in the temporal domain, which characters has been used in the numerical simulation methods, namely the fourth order Runge-algorithm, to study the OPCPA system operating in saturated amplification case. We take the LBO crystal as the nonlinear gain medium in the numerical simulation. The results showed as follows. The nonlinear phase shifting of the signal pulses occurred during the optical parameters process distrusted linearly around the central wavelength fraction. There exists a quasi-periodic structure in the power conversion efficiency, which originated from the phase mismatch among the pump pulse, signal and ideal pulse. And the maximal conversion efficiency occurs at the first peak conversion point. The contrast of the output femtosecond pulse reduced and the length of the pre-pulse enlarged as the degree of the saturated amplification severed.