为了提高再生放大器输出激光脉冲的对比度，需要同时提高激光脉冲纳秒尺度的对比度和皮秒尺度的对比度。利用普克尔盒对主脉冲和预脉冲时间滤波的方法，设计了普克尔盒的双通预脉冲清洁装置，通过该装置使再生放大器输出激光纳秒尺度的预脉冲对比度提高了5个数量级；利用频谱整形方法，通过在放大器腔内适当位置插入频谱整形滤波片使得主脉冲前400 ps处的放大自发辐射对比度提高了1个数量级。最终，在双通预脉冲清洁与腔内频谱滤波共同作用下，再生放大器输出激光纳秒尺度的预脉冲对比度从4.3×10^-4提高到了6.6×10^-10，放大自发辐射对比度（主脉冲前400 ps）从5.0×10^-8提高到了5.0×10^-9。

Two different pulse cleaning techniques for ultra-high contrast laser systems are comparably analysed in this work. The first pulse cleaning technique is based on noncollinear femtosecond optical-parametric amplification (NOPA) and second-harmonic generation (SHG) processes. The other is based on cross-polarized wave (XPW) generation. With a double chirped pulse amplifier (double-CPA) scheme, although temporal contrast enhancement in a high-intensity femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system can be achieved based on both of the techniques, the two different pulse cleaning techniques still have their own advantages and are suitable for different contrast enhancement requirements of different laser systems.