Low-reflection-loss attenuator optical coatings: theory and experiment.

Following the optical admittance matching approach, we have derived explicit equations to evaluate the refractive index and thickness of the matching dielectric layer deposited on an attenuator layer to obtain zero or near-zero reflection loss at one or more than one wavelength. With these equations a new family of optical coatings that can not only attenuate the input optical radiation to a required level but can also show a very low reflection loss (less than 0.1%) within a specified band is successfully designed and developed. Typical coatings, produced by electron-beam evaporation, have an average reflection loss of less than 1% and transmittance of 0.42 and 0.64 ± 0.02 over visible and near-IR spectral regions, respectively.