| Abstract [eng] |
As continuous wave (CW) lasers are improved and used in a broader spectrum of applications there has arisen a need to assure their quality. The latest research regarding continuous wave laser induced damage threshold was done in 1998, with the assumption that the material is damaged irreversibly once it reaches melting point. On the other hand, research in short pulse lasers has shown that optical coatings and subsurface defects of the substrate glass also have a significant impact on the damage threshold, but this has not yet been confirmed for CW lasers. The goal of this work is to estimate thermally induced stress and melting point, of coated or defected optical components, under CW irradiation, using numerical modelling software. It was observed that using a smaller beam diameter displays a stronger threshold fluence dependence on irradiation duration (within tested variable limits), than in the case of a larger beam diameter. Numerical modelling of UVFS samples has shown that subsurface defects under irradiation act as stress raiser, in addition their shape and position have a significant impact on the damage threshold. Under the assumption that generalized (von Mises) stress is an adequate stress criterion, it was determined that different damage phenomena become the most prominent under different irradiation duration. Investigation of gold coated UVFS substrate has shown that melting point damage threshold depends on irradiation duration and decreases with it even at short pulse range. |
