Laser Conditioning and Electronic Defects of HfO2 and SiO2 Thin Films

Abstract

Multilayer HfO2/SiO2 high reflectors (HR) and polarizers show a permanent increase in their 1064-nm damage thresholds following laser conditioning at subthreshold fluences. Threshold increases of 2–3x are typical. In an effort to better understand the conditioning effect we have made laser conditioning and electronic property measurements on single layers of these two materials. The laser damage threshold of 1-μm thick e-beam deposited SiO2 was increased by laser conditioning for wavelengths ranging from 355 to 1064 nm. The damage threshold of HfO2 single layers was not influenced by sub-threshold illumination. As-deposited thin films of a-SiO2 are known to contain paramagnetic electronic defects. We have used electron paramagnetic resonance (EPR) to study the concentrations and types of defects present in single layer and multilayer films of HfO2 and SiO2. E' and oxygen hole centers with concentrations on the order of 1017/cm3 have been measured in the SiO2 layers. A previously unreported defect has been observed for HfO2. The concentration of defects was studied both before and after laser conditioning and damage with 1064-nm photons. These electronic structure measurements are discussed in relation to an electronic defect model for laser conditioning of dielectric multilayers.

Continuous-wave laser particle conditioning: Thresholds and time scales

“…Although the exposure of contaminated optics to high irradiances often leads to catastrophic failure, lower irradiance exposure can have a beneficial conditioning effect on the optic [3,4]. Optics that have been laser-conditioned experience less heating and survive higher irradiances than non-conditioned optics [5].…”

Coupling effect of multi-wavelength lasers in damage performance of multilayer mirrors at 355 nm and 1064 nm

“…6a, the number of small pits grows because of the extra 1064 nm fluence. M. Zhou explained the phenomenon successfully with multi-defect statistical model [14,22], however, basing on the entirely different damage sites and mechanisms, we instead propose that the couple effect is associate with intrinsic electronic defects [23,24] as following. First of all, Proc.…”

Influence of the number of double layers on the damage threshold of Al 2 O 3 /SiO 2 and LaF 3 /MgF 2 mirrors at 248 nm

“…Inhomogeneous samples with too broad a i-on-i damage fluence range for meaningful statistics considering the given sample size were additionally tested for macroscopic damage after 100 pulses at 20 Hz. It was also attempted [8] to condition the coatings towards higher LIDT values by performing S-on-i and R-on-i irradiations at sub-damage fluence [9,10].…”

“…Compared to batch B, relative conditionability is lower and residual absorptance higher. Possibly, the improved purity of the vacuum and the lower e-gun energy reduced the amount of stoichiometric and electronic defects which are suspected to be annealable by laser irradiation [9,10] . The reduced substrate temperature during deposition may have caused the increased defect density and possibly other microstructural defects.…”