Publications

Design and development of laser damage resistant low group delay dispersion optical coatings for high reflection at 45o incidence P polarization and wavelengths from 800 to 1000 nm

Bellum, John C.; Field, Ella S.; Winstone, Trevor W.; Kletecka, Damon E.

This paper describes the modelling and design development of an optical coating that is suitable for broad bandwidth high reflection (BBHR) at 45° angle of incidence (AOI), P polarization (Ppol) and fs-class laser pulses whose frequencies correspond to wavelengths from 800 to 1000 nm, and that can eventually be produced uniformly on meter-class optical substrates. The coating design process was guided by specifications of not only high reflection but also high laser-induced damage threshold (LIDT) as well as low group delay dispersion (GDD) for reflected light over the broad, 200 nm bandwidth in order to minimize temporal broadening of the fs pulses upon reflection. The coating is based on TiO₂/SiO₂layer pairs by means of e-beam evaporation with ion-assisted deposition (IAD). We used OptiLayer Thin Film Software to explore coating designs with a limited optimization process starting from TiO₂/SiO₂ layer pairs with layer thicknesses in an opposite “chirp” arrangement. This approach proved to be successful, leading to a design with R > 99.5% from 801 – 999 nm and GDD < 20 fs² from 843 – 949 nm (45° AOI, Ppol). The GDD behaves in a smooth way that lends itself to compensation of GDD effects. Also, the electric field intensities are favorable to high LIDT in that they quench rapidly into the outer coating layers or are of moderate strength, or they are located in the higher band gap SiO₂ layers.