Absorption and damage thresholds of low-defect-density hafnia deposited with activated oxygen

Abstract

Motivation for this work included observations at Lawrence Livermore National Laboratory and elsewhere of a correlation between increasing laser damage thresholds (DT) and both decreasing nodular-defect density and absorption of coatings. We reduced the nodular-defect densities by a factor of over 4x in hafnia (HfO<SUB>2</SUB>) coatings deposited by reactive e-beam evaporation from a Hf target source. In order to increase the metal oxidation kinetics at the coated surface, Hf was e-beam deposited reactively with O<SUB>2</SUB> activated by a (mu) -wave discharge. The effect of using activated O<SUB>2</SUB> during the evaporation of a HfO<SUB>2</SUB> target source was also evaluated. A series of HfO<SUB>2</SUB> layers were made with various conditions; we alternated between two (mu) -wave configurations, Hf and HfO<SUB>2</SUB> targets and two reactive O<SUB>2</SUB> pressures. Laser DTs (1064 nm - 10 ns pulses), absorption (at 511 nm), and nodular- defect densities from these coatings are reported. The DT correlated inversely with the coating absorption.