Laser conditioning effect of HfO₂/SiO₂ film

Large aperture laser was used to irradiated the HfO₂/SiO₂ reflectors, which were evaporated from hafnia and silica by e-beam. Laser calorimeter was used to test the film absorption before and after laser irradiation. The results show that film absorption decreased from 5.4%, 1.7% to 1.4%, 1.2%, when the measurement wavelengths were 1 064 and 532 nm, respectively. Focused ion beam (FIB) was used to study the damage morphology after laser irradiation and to explore the cause of damage. The film where nodule existed was easily damaged, and the damage morphology mainly presented melt, partly erupted and absolutely fallen off. For the HfO₂/SiO₂ reflectors, laser conditioning was effective to eject the nodules on substrate. It was result from the nodule residue not to affect the subsequent laser. In addition, laser conditioning was not effective to the nodule in the film, which may be from the material spatter in coating process. In this case, other method can be used to get rid of the nodules.