Damage growth characteristics of artificial nodules prepared by different processes

Damage growth behaviors play an equal important role in limiting the laser resistance of high reflectors (HR) on high power laser systems as initial damage. In order to build damage mechanism and improve the laser resistance of coatings, it is necessary to obtain more information about damage growth behaviors. Thus a comparative experiment was designed to study the damage growth characteristics of different size of nodular defects in HfO2/SiO2 high reflectors working at 1 064 nm. Two kinds of HfO2/ SiO2 high reflectors were prepared by EB and IAD process, respectively, and four sizes of SiO2 microspheres were used to create artificial nodules in these films. Then the relationship between damage growth characteristics with nodule size and film deposition processes was studied. Laser damage test results showed that the damage growth threshold decreased with the increase of nodule size for all sizes of nodules in both EB and IAD coatings. The damage growth threshold were higher than the initial damage threshold for all four sizes of nodules in coatings prepared by EB process, however, the results were opposite for all four sizes of nodules in coatings prepared by IAD process. Besides, IAD nodules were more easily to grow than EB nodules, which indicated that the film deposition processes has some influence on the damage growth speed of nodules.