Annealing effects on microstructure and laser-induced damage threshold of quasi-rugate filters

Abstract

Ta₂O₅/SiO₂ quasi-rugate filters with high damage thresholds were deposited by ion-beam sputtering and then annealed at temperature of 200-800°C. The relations between microstructure, optical properties, chemical composition, weak absorption, and laser-induced damage threshold (LIDT) were studied. It was found that the transmittance spectra shifted to short wavelength as the annealing temperature increased. Three evolution courses of the films in the annealing process were analyzed by Atomic Force microscopy (AFM), Zygo interferometer measurement and Focused Ion Beam microscope (FIB). The decreased weak absorption during annealing process was found with significant effect on the LIDT. As the annealing temperature increased to 600°C, the weak absorption of films decreased from 39.99 to 7.2 ppm and the 50%-LIDTs increased from 59.32 to 158.87J/cm². Distinct damage micrographs of the films annealed at different temperature were obtained. A combination of substoichiometric defect and structural defect dominant description was used to illustrate the aggravation of laser-induced damage.

Hf1−xSixO2 Nanocomposite Coatings Prepared by Ion-Assisted Co-Evaporation Process for Low-Loss and High-LIDT Optics

“…Since the weak absorption was affected by the combination of defect absorption and the microstructure of the films [ 42 ], the combination of substoichiometric defect and structural defect dominant description was used to illustrate the evolution of the weak absorption, as is shown in Figure 7 . At annealing below 400 °C, the amorphous as-deposited Hf 1−x Si x O 2 film did not crystallize.…”

Multipass lock-in thermography for the study of optical coating absorption

“…The annealing of optical coatings is a classical way to modify the density [60], stoichiometry [61] and losses [62][63][64][65] of amorphous thin films. Therefore, we studied the effect of annealing conditions on the absorption of high-index materials.…”

“…The annealing treatments were conducted at atmospheric pressure and ambient atmosphere. Nb2O5 has a crystallization temperature around 400°C and Ta2O5 around 600°C [63][64][65][66]. Hence, different temperatures below 400°C were tested, to remain below the crystallization limit of Nb2O5.…”