交叉偏振波(XPW)技术是一种基于具有各向异性特征的三阶非线性晶体的非线性滤波技术,由于结构简单,稳定可靠,是超强超快激光领域提高时域对比度、压缩脉宽的有效手段之一.在实验中发现,XPW的输出特性受驱动脉冲特性的直接影响,通过理论计算得到了XPW的脉宽和光谱宽度与驱动脉冲的啁啾特性关系,同时利用声光可编程色散滤波器设计实验对理论计算进行了验证.结果表明:实验结果很好地反映了理论计算得出的结论,同时在饱和功率密度条件下,还表现出了一些理论计算没有反映出的新现象,即XPW的光谱展宽突破了驱动脉冲宽度√3倍的限制,最终脉宽也能够压缩至小于入射脉宽的1/√3;此外对于相反线性啁啾的驱动脉冲所产生的XPW信号,其在光谱形状上有明显的偏移差异,同时输出效率也有所不同.最后对这些新现象进行了进一步的分析和理论解释.%Ultra-short and ultra-intense laser is one of the hottest research spot of laser technology and strong field physics, due to its challenging and the frontier application research. As the key specification of ultrafast ultrahigh intensity laser pulse, the contrast ratio is very influential on the effect of laser-matter interaction. To perform the laser-matter interaction experiments at a high power level, the contrast is required to be as high as 1010 to prevent preplasma dynamics. To solve these problems, one has proposed many methods to improve the contrast of ultrafast laser, such as using the saturable absorbers, double chirped pulse amplification, plasma mirrors and the cross-polarized wave (XPW) generation. The XPW technology can not only enhance the contrast of the pulse by 3–4 orders of magnitude without introducing any space dispersion, but also extend the output spectrum to support shorter pulse duration. The XPW is a nonlinear filter technique in third-order nonlinear crystal with anisotropic susceptibility. Because of its simple and all-solid-state structure, the XPW technique has become one of the most effective methods to enhance the temporal pulse contrast and deliver shorter pulse duration in the field of high peak-power ultrafast lasers. This method has been used in many large laser facilities under construction or upgrades, such as the Apollon and ELI, the contrast ratio as high as 1010 has been achieved. It is known that the conversion efficiency and spectral characteristics of XPW have a strong dependence on the spatial and temporal magnitudes of the input driving pulse. In our experiment, it is found that the various changes of the driven pulse properties have different influences on the characteristics of XPW pulses. The relationship between the linear dispersion of driven pulse and temporal property of XPW is investigated theoretically. In addition, an experiment on verifying the theory is conducted by taking advantage of a programmable acousto-optic dispersion filter. The experimental results fit well to the theoretical results while some new phenomena emerge when the intensity in the BaF2 crystal reaches a saturation threshold. The spectral broadening capability of XPW becomes stronger and exceeds a theoretical upper limit. The pulse width can also be compressed to shorter than the theoretical limit. It is found that there are significant differences in spectral shape and conversion efficiency between the XPW signals by applying the opposite linear chirps to the driving pulse. A further analysis and theoretical explanation of these new phenomena are also presented.
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