Development of damage resistant optics for KrF excimer lasers

At excimer wavelengths the photon energy either exceeds or is comparable to bandgap energies of most materials. This severely limits the materials suitable for optical coatings and is also responsible for the rapid decrease in observed damage threshold fluences as laser wavelength drops. Most materials traditionally used in coating fabrication are unsuitable at the shorter excimer wavelengths. For longer wavelength coatings materials are chosen for properties such as index contrast and ease of deposition. We are currently reevaluating the suitability of selected materials for damage resistant optical coatings at the KrF excimer wavelength. The low and medium index fluorides are promising as is aluminium oxide. We report the results of damage experiments on both single layer films and dielectric reflectors fabricated from promising combinations of these materials. 1.