Properties of Laser Mirrors at Non-normal Incidence

For laser mirrors made out of lossless periodic dielectric mutlilayers, having a basic period of two layers (ZnS and MgF₂) with different refractive indices and equal effective optical thicknesses, both the reflectivity at the stopband centre and the width of the stopband are calculated as a function of the angle of incidence for radiation polarized perpendicular or parallel to the plane of incidence. The results of computer calculations for mirrors with up to 20 layers are presented in a number of graphs and are discussed in detail. The graphs simplify the design of laser mirrors according to prescribed specifications and make it possible to distinguish between a maximum or a minimum of the spectral reflectivity at the centre of the stopband.