Mechanism of original damage of thin optical components induced by surface particle contamination

Abstract

Based on the optical transmission theory, the reason why front-surface particle contamination may induce the original damage of thin optical components is considered, and a damage mechanism is put forward: The localized thermal deformation of an optical element induced by the thermal effect of particle contamination together with the shading effect of it can disturb the laser beams. Simulated results show that for a high power laser, the localized thermal deformation of thin optical components, which disturbs the laser beam, is an important cause to produce strong light intensity modulations. The surface shape, phase delay, and thermal diffusion length of a localized thermal deformation are constantly changing with the increase of laser pulse shot number, so the highest light intensity modulation will be produced at different positions in the thickness direction or the xy direction on the rear-surface of an optical element. This not only can easily induce some damages on the rear-surface of the optical element, but also cause the interior damages scattered in the thickness direction.

Influence of secondary treatment with CO 2 laser irradiation for mitigation site on fused silica surface

“…[1] With the improvement of facility fluence, the various defects (such as scratches, indentations) and contaminations on optics will lead to the various negative effects on the system. For example, the formation of a strong light field resulting from the light modulation of defects, [2] the appearance of localized high temperature because of laser energy absorbed by impurities, [3] etc., each will lead to an easier damage event of optics. Moreover, the catastrophic damage will occur if the initiation damage grows under the subsequent laser shots, leading to the great loss of performance of optics, such as transmission, damage resistance ability.…”