Abstract

Low-loss dielectric mirrors for wavelengths between 130 and 250 nm were developed using conventional deposition, IAD and IBS. Firstly, single layers of SiO₂, Al₂O₃, HfO₂, AlF₃, MgF₂, LaF₃, NdF₃ and GdF₃ were deposited. The refractive indices, extinction coefficients and packing densities of the layers were determined by spectrophotometric methods in order to investigate their dependence on deposition parameters. At HR-coatings, the reflection coefficients were measured and compared to values calculated from single layer data and interface roughness data. At 248 nm, the highest reflectivities were achieved with conventional as well as ion-beam- sputtered oxide mirrors. At wavelengths below 200 nm, conventionally deposited fluoride mirrors yielded the best results. Their reflection losses are mainly due to interface scattering. Fluoride mirrors deposited by IBS show substantially reduced scattering, but their reflectivities are decreased by absorption losses. At mirrors for 193 and 248 nm, the damage thresholds were measured. The highest values were obtained with conventionally deposited fluoride mirrors.

© 1991 Optical Society of America