Scattered light in reflective and refractive optical systems

A scalar theory, verified by the Rigorous Coupled Wave Analysis (RCWA), is used to compare the performance of optical surfaces with a specified roughness. It is shown that for surfaces with identical micro roughness structures, backward scattered light level for a reflecting surface is much higher than the forward scattered light produced by the surface of a refractive optical element made from typical optical glass. This implies that application of refractive components (such as transmission gratings and lenses) in optical systems where scattered light background is a limiting factor of the instrument performance may be advantageous over reflective components such as reflection gratings and mirrors.