Laser damage of optics in high power manufacturing applications the road from single-shot to billion-shot performance

Abstract

Laser-induced damage of optical materials hinders both the development and practical application of high-power lasers. This paper reviews damage induced by pulsed excimer lasers. Most previous damage studies have addressed the `time-zero' performance limits of optical materials. i.e., virgin samples exposed to one or a small number (N≲ 1000) of laser pulses. In this `single-shot' damage regime, coatings are almost always the weakest link in the optical system. Considerable progress has been made in identifying optimum coating materials and material combinations for particular wavelengths, and in exploring effects of undercoats and overcoats, non-quarter-wve designs, laser pre-conditioning, and alternate polishing and deposition methods on the measured damage threshold. However, adequate singe-shot damage resistance is a necessary but not sufficient condition for many practical applications. For the past few years at IBM, we have been studying long-term interactions of KrF laser radiation with deep UV optical materials, including fused silica glass, single-crystal quartz single-crystal fluorides, and various AR and IIR coating structures. The IBM results at 248 nm will be compared to results form other labs at both 248 and 193 nm. Implications for materials processing and Deep UV lithography will be discussed.