Characteristics of beam waveguides

The performance of beam waveguides is analyzed in terms of spillover losses, cross-polarization generation, and beamwidths as a function of illumination taper, mirror separation, and mirror F/D. The effects of protective paint on the mirror surfaces are also analyzed, and it is shown that the paint depolarizes the guided beam; this effect is particularly severe since four mirrors inclined at 45 deg are involved. If a coating is required, its thickness should be less than 0.0015 lambda to prevent excessive depolarization.