强光辐照下主镜表面散射引起的视场内杂光分布

Distribution of in-field stray light due to surface scattering from primary mirror illuminated by intense light

在强光辐照情况下,主镜表面粗糙度产生的散射是引起反射系统视场内杂散光的主要因素之一。本文针对主镜的散射,提出了一种简单的处理方法。采用双向散射分布函数(BSDF)描述散射的角分布特性,推导了平行光平行于光轴入射时主镜焦平面上的散射光强分布表达式,并将其与衍射光强分布表达式联立,得到了焦平面上以几何像点为中心,散射与衍射强度相等时的特征半径。该特征半径将焦平面上的光强分布分为两个区域,在强光辐照下这两个区域的饱和效应机理不同:特征半径以内,衍射强度大于散射强度,饱和效应主要由衍射贡献;特征半径以外,散射强度大于衍射强度,散射是该区域饱和的主要因素。仿真实验表明,对于半径为115 mm,焦距为-757 mm,入射波长为550 nm时表面粗糙度为10 nm的主镜,其特征半径约为0.843 mm,该结果与表达式计算结果相符,说明了计算表达式的正确性。

Light scattered from the imperfect surface of a primary mirror in a reflective optical system will result in the in-field stray light and reduce the image contrast.This paper presents a simple method to process the scattering of the primary mirror.A Harvey Bidirectional Scatter Distribution Function（BSDF） model is used to characterize the angular distribution of scattered light from the mirror,and the scattering distribution at the focal plane of the primary mirror is derived.The characteristic radius centered by the image point can be achieved when the intensity of scattering equals that of diffraction.It is found that for the given optical system,the characteristic radius only depends on the scattering characteristic of the primary mirror.The intensity distribution at the focal plane is divided into two regions by the characteristic radius.The intensity of diffraction is larger than that of scattering intensity,which makes the dominant contribution to the saturation effect when the distance from the image point is less than the characteristic radius,conversely,the scattering is the main factor to the saturation effect when the distance from the image point is larger than the characteristic radius.For a primary mirror with a focal length of-757 mm,an radius of 115 mm and the rms roughness of 10 nm at the wavelength of 550 nm,the characteristic radius is 0.843 mm approximately.These conclusions are conductive to the analyzing and explaining of the saturation effects in an optical system irradiated by a intense light.