轴锥镜光强分布的角谱衍射数值分析法

针对理论上推导轴锥镜的衍射光场分布解析式较为困难，且用菲涅耳衍射理论分析时存在近轴近似及不能适用于近场衍射光场分析的问题，采用了严格遵从标量衍射亥姆霍兹方程的角谱衍射波前重建方法，对轴锥镜在单色和准单色高斯光波照射下的横向和轴向衍射光强分布特性，以及在单色均匀平面光波照射下的轴向衍射光强分布进行了数值计算和分析。结果表明，轴锥镜后单色光衍射光强分布在几何光束重叠的菱形区域内为近似无衍射贝塞尔光强分布，轴上光强沿光轴方向呈振荡变化，轴上光强分布规律与入射光波的垂轴横向光强分布有关；入射光的准单色性使得贝塞尔衍射条纹对比度略下降、轴上光强沿光轴方向振荡程度减小，但分布规律与单色光一致。

Intensity Distribution Analysis of Axicon Lens by Numerical Angular Spectrum Method

The lateral and on-axis diffractive intensity distributions of an axicon lens illuminated by the monochromatic and quasi-monochromatic Gaussian beams are numerically calculated and discussed by using the angular spectrum method. Also, the on-axis diffractive intensity distribution of the axicon illuminated by uniform monochromatic plane wave is given. Unlike the well-known Fresnel diffraction integral, the propagation theory of angular spectrum defers to the more rigorous Helmholtz scalar wave equation with fewer approximation, resulting in more accurate results. The results of numerical calculation show that the intensity distribution of diffractive field in the rhombic region determined by the overlap of light rays has the characteristics of diffraction-free Bessel beam. The intensity on the optical axis changes in a fluctuating way which shows direct correlations with the lateral intensity distribution of the incident waves. In the quasi-monochromatic case, the contrast of Bessel fringes and the degree of fluctuation of on-axis intensity tends to decrease slightly, depending on the bandwidth of incident beam, while the intensity distribution keeps the same form as the monochromatic case.