Study of laser-induced damage at 2 microns on coated and uncoated ZnSe substrates

Abstract

Laser damage characteristics of infrared substrates and coatings at 2-micron wavelength have been rarely studied until yet, even if the need of optical components with high laser-induced damage threshold in the mid-infrared is important. Use of an infrared nanosecond laser, tunable in the range 2 to 5 microns, allowed us to develop an automatic test facility for the determination of accurate LIDT curves for different test procedures. We choose to particularly study polycrystalline zinc selenide (ZnSe) material used as substrates for infrared dielectric coatings. Irradiation of ZnSe substrates with parallel laser beam shows that surfaces always break clearly before bulk material, this shows that surfaces must be carefully prepared. We particularly exhibit the influence of polishing processes on substrates LIDT. Then the influence of different cleaning methods before coatings deposition is studied. Practical implications for the fabrication of highly laser resistant multilayer coatings at 2-microns are finally discussed.