Heterostructure films of SiO$_2$ and HfO$_2$ for high power laser optics prepared by plasma-enhanced atomic layer deposition

TL;DR

This study develops SiO₂/HfO₂ heterostructure films via plasma-enhanced atomic layer deposition, achieving improved optical and damage resistance properties for high-power laser optical coatings.

Contribution

It introduces a novel PEALD method to create heterostructure films with tunable optical properties and enhanced laser damage thresholds for high-power laser applications.

Findings

Heterostructures exhibit tunable refractive index and bandgap.

Films show improved optical losses and laser-induced damage threshold.

Successful incorporation into antireflection coatings with high damage resistance.

Abstract

Absorption losses and laser-induced damage threshold (LIDT) are considered as the major constraint for the development of optical coatings for high-power laser optics. Such coatings require paramount properties like low losses due to optical absorption, high mechanical stability, and enhanced damage resistance to withstand high-intensity laser pulses. In this work, heterostructure films were developed by the intermixing of SiO$_2$ and HfO$_2$ using plasma-enhanced atomic layer deposition (PEALD) technique. Thin film characterization techniques such as spectroscopic ellipsometry, spectrophotometry, substrate curvature measurements, x-ray reflectivity, and Fourier transform infrared spectroscopy were employed for extracting optical constants, spectral inter-pretation, residual stress, layer formation, and functional groups present in the heterostructures, respectively. These heterostructures demonstrate tunable refractive index, bandgap, and improved optical losses and LIDT properties. The films were incorporated into antireflection coatings (multilayer stacks and graded index coatings) and the LIDT was determined at 355 nm wavelength by the R-on-1 method. Optical absorptions at the reported wavelengths were characterized using photothermal common-path interferometry and laser-induced deflection techniques.