Submicrometer-resolution mapping of ultraweak 355-nm absorption in HfO2 monolayers using photothermal heterodyne imaging

Nanosecond-pulse UV-laser-damage initiation in multilayer coatings comprised from metal oxide as a high-index component, and silica oxide as a low-index material, is strongly linked to metal oxide. The nature of the absorbing species and their physical properties remain unknown because of extremely small sizes. Previous experimental evidence provided by high-resolution mapping of damage morphology points to a few-nanometer scale of these absorbers. This work demonstrates submicrometer mapping of 355-nm absorption in HfO 2 monolayers using a recently developed photothermal heterodyne imaging technique. Comparison of absorption maps with spatial distribution of UV pulsed-laser- induced damage morphology allows one to better estimate the size and densities of nanoscale absorbing defects in hafnia thin films. Possible defect-formation mechanisms are discussed.