In situ measurement on ultraviolet dielectric components by a pulsed top-hat beam thermal lens

A simple and sensitive mode-mismatched thermal lens (TL) technique with a p ulsed top-hat beam excitation and a near-field detection scheme is develope d to measure in situ the thermoelastic and the thermooptical responses of u ltraviolet (UV) dielectric coatings as well as bulk materials under excimer laser (193- or 248-nm) irradiations. Owing to its high sensitivity, the TL technique can be used for measurements at fluences far below the laser-ind uced damage threshold (LIDT). We report on the measurement of both linear a nd nonlinear absorption of the UV dielectric coatings and bulk materials as well as the investigation of time-resolved predamage phenomena, such as la ser conditioning of highly reflective dielectric coatings and irradiation-i nduced changes of a coating's various properties. The pulsed TL technique i s also a convenient technique for accurate measurement of the LIDT of diele ctric coatings and for distinguishing different damage mechanisms: thermal- stress-induced damage or melting-induced damage. (C) 2000 Optical Society o f America OCIS codes: 120.6810, 140.3440, 310.6870.