Laser damage of optical components - Physics and metrology

High-power lasers are used in a wide range of applications in industry, science, medicine and defense. One of the technological obstacles to the development of high-power or high-energy laser sources is the damage caused to optical components by laser radiation. Indeed, when an optical component is subjected to intense laser flux, reversible phenomena such as non-linear effects or heating may be observed, leading to stresses and deformations that may alter the optical function during use. Increasing flux density can lead to irreversible effects: melting, vaporization, fracturing, craters, delamination, surface contamination... permanently altering the optical function of the component, or even rendering it unusable. These permanent changes to the material correspond to what can be defined as "laser damage".

This phenomenon limits the power output of laser sources, and can affect the service life of optical components, and consequently the maintenance costs of laser systems. It can also cause serious safety problems in laser installations. Knowledge of the physical phenomena involved as a function of laser parameters, and measurement of these effects, is therefore of major importance in designing a laser system and operating it under optimum conditions.

The problem of flux withstand has been studied since the invention of the laser, and there is a substantial database on the subject . In this article, we propose a synthetic approach to this subject, necessarily limited, but which will enable the engineer or researcher confronted with the problem to become familiar with the notions linked to the field, the physical phenomena involved and the way in which these effects can be quantified and the measurements related to its application.

First, we'll explain the various physical mechanisms that can lead to the destruction of an optical component subjected to laser flux, a necessary step in understanding and interpreting the measurements. We will then describe the methods used to measure the resistance to laser flux, and discuss their interpretation and the influence of laser parameters on damage. Finally, we will briefly present the materials and manufacturing processes specific to high-laser-flux components.