将夫琅禾费衍射理论与几何散射(包括折射和反射)相结合,给出平行光入射下圆形颗粒在前向大角度范围内的散射光强分布近似算法。由于考虑了衍射、折射和反射相互间的干涉效应和颗粒对光的吸收性,对于正常或非正常衍射状态下无因次参量α≥40的耗散颗粒,在前向0°～60°散射之内,该方法对散射光强计算结果与米氏理论结果是吻合的。由于计算速度比米氏理论快,有效角度范围比夫琅禾费衍射理论宽,因而适合于大颗粒的前向光强计算。将这一计算方法应用到大角度采光时的激光粒度测量实验中,收到了良好的效果。

The whole-geometric-approximation-method(WGAM) is presented to compute the forward light intensity. Since Fraunhofer diffraction and geometric scattering are combined, such a method is applicable under anomalous or normal diffraction regime. Due to the consideration of interference between the diffraction, refraction and the reflection rays, the calculable angle range is extended to 0°～60°. Because of its high calculation efficiency and wide validity range, WGAM is especially effective for light pattern calculation of the large particles with size parameter α larger than 40. Numerical calculations show that the results of WGAM are consistent with Mie theory. The experiments also find that WGAM can be applied in laser particle sizing based on large-angle forward scattering method.