Proceedings Article | 16 November 2018
Proc. SPIE. 10805, Laser-Induced Damage in Optical Materials 2018: 50th Anniversary Conference
KEYWORDS: Thin films, Silica, Polarization, Laser induced damage, Interfaces, Optical coatings, Laser damage threshold, Thin film coatings, Laser optics, Camera shutters
A kind of HfO2/SiO2 355nm and 1064nm high-reflective (HR) coatings were deposited by electron beam evaporation. Laser-induced damage of the coatings were tested by 355nm-7ns pulses, 355nm-1ns pulses and 1064nm-30ps pulses in 1-on-1 mode. All tests were carried out with S-polarized and P-polarized pulses in two angles of incidences (AOIs) of 30° and 50°. Damage morphologies and cross-sectional profiles were characterized using scanning electron microscope (SEM) and focused ion beam (FIB), respectively. It is shown that the typical morphologies in all the tests were μm-sized pits. In the 1064nm-30ps tests, the damage pits appeared mostly as 3-4μm ripple-like pits with a density of 13000-25000 mm<sup>-2</sup>, accompanied by a few tiny pits around. The ripple-like pits were all conical pits with a cylindrical cavity at the bottom, the depth of which was around 1μm. The tiny pits were all cylindrical shaped with a depth of about 400nm. In the 355nm-7ns tests, most of the pits were flat-pits scaled from 4 to 18μm with a density of 500-900 mm<sup>-2</sup>, few with a bulge in the bottom. The depth of the pits increased with their size, which can be 2.5μm for the largest ones. In the 355nm-1ns tests, pits appeared to be similar with those in 355nm-7ns tests, with a smaller size of 4-6 μm, The damage pits were preliminary inferred to be formed because of the material removal induced by the thermal stress.
