高斯光束通过非线性介质后的远场衍射图样的研究

 利用菲涅尔－基尔霍夫衍射积分公式，对发散和会聚高斯光束通过薄非线性介质时形成的远场衍射图样进行了研究。模拟计算结果表明：当发散高斯光束通过自散焦介质或会聚高斯光束通过自聚焦介质时，远场均会出现中央较暗、向外围逐渐增强、分布尺度较大的粗衍射环；当发散高斯光束通过自聚焦介质或会聚高斯光束通过自散焦介质时，远场均会出现中心强度最大、向外围逐渐减弱、分布尺度较小的细衍射环。不同远场衍射图样归根结底是入射高斯光束因介质折射率变化造成的空间自相位调制及其波前曲率共同作用的结果。

Far-field diffraction patterns formation of gaussian beam transmitted through thin nonlinear medium

Based on the Fresnel-Kirchhoff diffraction theory, this paper calculated the intensity distribution of the far-field diffraction patterns when a divergent or a convergent gaussian beam transmitted through a thin nonlinear medium, and analyzed the effect of the different Kerr mediums and the different gaussian beams on the patterns formation. The simulation results show that, when a divergent gaussian beam transmits through a defocusing nonlinear medium or a convergent one through a focusing nonlinear medium the pattern in the far field is a series of thick, larger diffraction rings with a central dark spot, while when a divergent gaussian beam transmits through a focusing nonlinear medium or a convergent one through a defocusing nonlinear medium the pattern in the far field is a series of thin, narrower diffraction rings with a central light spot. The difference between the diffractive patterns is attributed to the interaction of the strong spatial self-phase modulation caused by the refractive index change of the medium with wave-front curvature of the input gaussian beam. The results are significant to the design of practical optical limiters for the eye and sensor protection.