Glancing incidence measurements of diamond turned copper mirrors

The absorptance characteristics of diamond turned copper mirrors are measured at angles of incidence from 0 to 87 degrees . The measurements are performed at 1.06 microm for both s and p polarization and for the diamond turned grooves on the mirror surface oriented either perpendicular or parallel to the plane of incidence. To first order, the absorptances tend to follow the theoretical curves predicted by the Fresnel equations for flat bare metal surfaces. However, at glancing incidence, the Fresnel equations tend to have difficulty accurately predicting the experimental results. When the grooves are oriented perpendicular to the plane of incidence, the measured absorptance for s-polarized light is significantly higher than that predicted by theory; whereas the absorptance is slightly lower than theory when the grooves are parallel to the plane of incidence. Possible explanations for the observed absorptance behavior are discussed.