非线性介质表面缺陷对激光光场的调制

Modulation of nonlinear medium with surface defects on intensity properties of laser

以高斯光束为例,研究了非线性介质表面振幅调制型缺陷对光场的调制。基于广义惠更斯-菲涅尔衍射积分并采用泰勒级数展开方法,建立了高斯光束经过表面存在缺陷的非线性介质后的传输模型,得到了受缺陷调制光束经非线性介质后的光强分布解析式,研究了缺陷尺寸和光束在非线性介质中产生的附加相移大小对光强分布的影响,结果表明介质表面的缺陷尺寸越大,介质内产生的附加相移越大,光场受到的调制越严重。分别考虑了非线性折射率为正值和为负值的情况,研究发现相应的折射率值导致光束发生会聚或发散现象,并由于缺陷调制的作用,在光束传输过程中始终存在一光强极值点,且随着附加相移绝对值的增大光强极值点的峰值也随之增强。

This paper studies the modulation of the amplitude modulating nonlinear medium defects on a Gaussian beam. Based on the Fresnel diffraction integral and Taylor series expansion, the model of the beam propagating through the nonlinear medium with defects is built, and the analytical expressions for the intensity distribution at different distance of a Gaussian beam getting through the defective nonlinear medium are derived. The impact of the defect size and the additional phase shift in the me- dium on the intensity distribution of the beam propagating through the medium is studied. It is shown that larger defects and more additional phase shift lead to deeper beam modulation. Under the modulation of the defects and the nonlinear effect in the medi- um, there would be a maximum intensity near the rear surface of the nonlinear medium before the beam convergence or diffusion, when the medium has positive or negative nonlinear index of refraction, and the larger the phase shift of the beam is in the medi- um, the stronger the maximum intensity becomes.