<title>High laser-induced damage threshold polarizer-coatings for 1054 nm</title>

Abstract

Polarizer coatings developed for the OMEGA laser are performing well without sustaining any significant damage. Similar polarizers developed for the National Ignition Facility have exceptionally high damage thresholds when tested with a 1-ns pulse at 1054 nm. Polarizers for OMEGA were originally developed using Ta<SUB>2</SUB>O<SUB>5</SUB>/SiO<SUB>2</SUB> multilayers. All final polarizers before the frequency conversion cell were made using this method. A new coating was developed for a polarizing beamsplitter with more stringent optical and laser-damage requirements. The new coating used a HfO<SUB>2</SUB>/SIO<SUB>2</SUB> system with the hafnia formed by reactive evaporation from a hafnium metal melt. The new process provided better film control, lower defect counts, better stress control, and higher damage thresholds. Beamsplitter coatings made from both processes were installed in the OMEGA laser. After 1.5 years of operation the Ta<SUB>2</SUB>O<SUB>5</SUB>/SiO<SUB>2</SUB> beamsplitters are developing signs of damage on OMEGA while the HfO<SUB>2</SUB>/SiO<SUB>2</SUB> coatings show no damage. The HfO<SUB>2</SUB>/SiO<SUB>2</SUB> process was also used to develop polarizer coatings for the NIF. Damage- threshold results from 1-on-1 testing will be presented for both types of polarizers. Experimental results show that the coating damage threshold is not strongly dependent on deposition parameters, allowing use of these parameters to control film stress. The damage thresholds are higher for s- polarized incident light, and different damage morphologies for the two polarizations have been observed. A base layer of scandium oxide that allows the coating to be safely stripped does not affect the polarizer damage threshold.