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Hafnium oxide (HfO 2) is the most frequently used high-index material in multilayer thin-film coatings for high-power laser applications ranging from near-infrared to near-ultraviolet (UV). Absorption in this high-index material is also known to be responsible for nanosecond-pulse laser-damage initiation in multilayers. In this work, modification of the near-UV absorption of HfO 2 monolayer films subjected to irradiation by continuouswave (cw), 355-nm or 351-nm laser light focused to produce power densities of the order of ∼100 kW∕cm 2 is studied. Up to a 70% reduction in absorption is found in the areas subjected to irradiation. Temporal behavior of absorption is characterized by a rapid initial drop on the few-tens-of-seconds time scale, followed by a longerterm decline to a steady-state level. Absorption maps generated by photothermal heterodyne imaging confirm the permanent character of the observed effect. Nanosecond-pulse, 351-nm and 600-fs, 1053-nm laser-damage tests performed on these cw laser-irradiated areas confirm a reduction of absorption by measuring up to 25% higher damage thresholds. We discuss possible mechanisms responsible for near-UV absorption annealing and damage-threshold improvement resulting from irradiation by near-UV cw laser light.

Resonant cavity detectors based on III–V materials have been designed, grown entirely by molecular beam epitaxy, fabricated, and tested. They offer a low noise (dark current densities of 0.4 mA/cm2 were measured at 298 K, close to the predicted value of 0.31 mA/cm2), narrow response detector (full width at half maximum of 57 nm in GaSb and 45 nm in InAs) in the mid-infrared region, with future applications in spectroscopy, gas sensing, and optical communications.