Laser damage resistance of optical coatings in the sub-ps regime: limitations and improvement of damage threshold

Abstract

We introduce the topic of short-pulse laser damage in optical coatings in order to understand the intrinsic limitations depending on the application, and the possibility of laser damage resistance improvement. Firstly we describe the physical process of a high intensity femtosecond laser pulse interaction with an optical coating and how this interaction can lead to a damage of the film. Then we present the main facts about laser damage resistance of coatings that are relevant for applications and related to the previously described processes: the dependence of the Laser-Induced Damage Threshold (LIDT) of coating materials with bandgap, the decrease of LIDT with the pulse number, the wavelength and pulse duration dependence, etc... We also discuss on the question of the role of macroscopic defects on damage initiation in this regime and damage growth under multiple irradiation. Eventually different strategies to improve the laser damage resistance will be discussed: engineering of the electric field distribution in the stack, fabrication of mixture materials with enhanced LIDT, mitigation of defects.