Abstract

A series of five broadband antireflection coatings on zinc selenide substrates was deposited with or without ion-assisted deposition at a substrate temperature of 220°C. Measurement of laser damage threshold for 10.6-µm, 0.1-µs pulses were made on these coatings. Significant improvements have been made in increasing the durability and laser damage threshold of broadband AR coatings by using the ion-assisted deposition of the zinc selenide films. Coatings prepared using this technique consistently passed the environmental tests for adhesion, 24-h salt spray, and 10-day humidity tests specified by MIL-C-675 and MIL-M-13508. The experimental data indicate that the damage threshold can be increased by using the ion-assisted deposition and by optimizing deposition parameters such as temperature and pressure. The absorption was normally reduced by baking the coatings at the temperature of 300°C in air. Baking increased the damage thresholds of some coatings, especially those which initially had noticeably large absorption. Using the ion-assisted deposition, the zinc selenide films were strengthened by increasing packing density and reducing columnar microstructure. Therefore, it is concluded that the ion-assisted deposition of zinc selenide films definitely increases the laser damage threshold of broadband AR coatings on zinc selenide substrates.

© 1989 Optical Society of America