Extreme broadband dichroics: Monte Carlo transmission line modeling for astronomical spectroscopy

Dichroic beamsplitters, or dichroics, rely on the optical interference that occurs within thin-film layers to ensure the separation of the transmission and reflection of selective wavelengths of an incident beam of light at a given angle of incidence. Utilized within the optical systems of numerous space telescopes, they act to separate the incoming light spectrally and spatially into various channels. As space missions increasingly demand simultaneous observations across wavebands spanning extreme wavelength ranges, the necessity for exceedingly complex broadband dichroics has emerged. Subsequently, the uncertainties pertaining to their optical performance have also become more intricate. We use transmission line modeling to evaluate the spectral performance of multilayer coatings deposited on a substrate material for given thicknesses, materials, angles of incidence, and polarization. A dichroic recipe in line with the typical specifications and requirements of a dichroic is designed with the aid of a Monte Carlo simulation. The tolerances of the coating performance to systematic and random uncertainties from the manufacturing process, as well as from environmental changes in space, are studied. With the aid of accurate manufacturing recipes and uncertainty amplitudes from commercial manufacturers, this tool can predict variations in the optical performance that result from the propagation of each of these uncertainties for various hypothetical scenarios and systematic effects.