基于YCOB晶体分析信号光脉冲时间特性对光参变啁啾脉冲放大光谱和转换效率的影响

基于YCOB晶体中三波耦合方程理论模型,在抽运光波形和能量、晶体长度相同的条件下,研究信号光的时间波形对光参变啁啾脉冲放大(OPCPA)光谱和转换效率的影响。计算过程中,抽运光和信号光能量分别为45J和500mJ,光斑直径分别为60mm和50mm。抽运光脉宽取3ns,信号光脉宽为1.2ns。数值结果显示,信号光放大后的光谱和转换效率与输入信号光的时间波形有关。1阶高斯型脉冲光谱的半峰全宽(FWHM)得以展宽,由原来的36nm展宽为放大后的61nm,2阶超高斯脉冲频谱展宽为47nm,高斯脉冲的阶数越高,谱宽展宽越小,5阶和5阶以上的高斯脉冲光谱不再展宽,几乎保持原来36nm不变;1阶高斯脉冲的转换效率最高,达到32%左右,2阶高斯脉冲只有25%,8阶以上转换效率基本变化不大,约为19%。信号光脉冲时间特性对OPCPA的光谱输出和转换效率产生很大的影响。

Analysis of Optical Parametric Chirped Pulse Amplification Spectrum and Conversion Efficiency Resulting from Time Characteristics of Signal Pulse Based on YCOB Crystal

The impact of time-domain properties about the signal pulse on spectrum and conversion efficiency after optical parametric chirped pulse amplification (OPCPA) is studied, based on coupled equations in YCOB crystal, when pump energy and pulse shape are certain. The energies of pump and signal pulse are 45 J and 500 mJ, and beam diameters are 60 mm and 50 mm, respectively, during the calculation. Pulse width of pump pulse is 3 ns, while signal′s is 1.2 ns. The numerical results show that signal spectrum amplified and conversion efficiency are related to time-domain properties of input signal pulse. The spectral full width at half maximum (FWHM) after OPCPA is broadened from 36 nm to 61 nm when the signal pulse as one order Gaussian pulse, but that of two order Gaussian pulse is just broadened to 47 nm. The order is higher, broadening is less. The FWHM keeps almost unchanged at 36 nm, compared with that before OPCPA when the signal pulse as five even higher order Gaussian function. And when the length of YCOB crystal is constant, conversion efficiency reaches 32% when the signal pulse as one order Gaussian pulse, with that of two order Gaussian pulse is only 25%. That of eight order Gaussian pulse or above changed little, remaining approximately 19%. Temporal characteristics of signal pulse make great fluence on the spectrum and conversion efficiency of the amplified pulse when the pump pulse and the length of the crystal are certain.