拼接光栅缝隙对激光脉冲光强分布的影响

Laser pulse pattern influenced by mosaic grating gap

以拼接光栅作为色散元件的激光脉冲压缩器中,要求脉冲压缩光栅表面光强分布均匀、能量输出效率高。利用菲涅耳-基尔霍夫衍射原理对脉冲压缩光栅表面光强和远场光强分布进行了研究。计算了拼接光栅缝隙宽度对光栅表面光强变化量和远场光强极大值的影响。在利特罗角附近入射时发现激光脉冲光强分布与拼接光栅缝隙宽度相关,得出了光栅拼接缝隙宽度应控制在0.5mm以内。适当提高缝隙衍射效率能够改善光强分布均匀性和提高光能量输出,提出了对拼接缝隙采用两次重复曝光以提高其衍射效率的方法。

High energy efficiency and well-distributed output on the surface of the chirped pulse grating are required in the laser pulse compressor with mosaic gratings as the dispersion element.Fresnel-Kirchhoff＇s diffraction theory is utilized to study the light distribution on the grating surface and the far-field diffraction pattern.The variations of the light intensity on the grating surface and the maximum value of the far-field light intensity influenced by the mosaic grating gap are calculated.It is found that the light distribution is related to the width of the gap for light incidence near the Littrow angle,and the width of the gap should be limited within 0.5 mm.When the diffraction efficiency of the gap increases,the light distribution will be more uniform and the output energy can be enhanced.Thus a method of twice holographic exposure is proposed to increase the diffraction efficiency of the gap.