Low-Loss Multilayer Dielectric Mirrors

Abstract

The preparation of low-loss multilayer dielectric coatings for laser mirrors is described. Layer thickness is controlled by a unique monitoring system utilizing a 6328-Å gas laser as a light source. Experiments designed to evaluate and reduce losses in the mirror coatings are discussed. It is found that mirror transmission losses may be reduced to a negligible value by deposition of a sufficient number of dielectric layers, without at the same time increasing scattering and absorption losses. Reflectivities in excess of 99.8% have been obtained from a single stack of twenty-five quarter-wave layers. Broad-band mirrors with reflectivities greater than 99.5% from 4300 Å to 7400 Å have been produced by properly stacking two such twenty-five-layer groups.