Influence of thickness and wavelength on Laser Damage Threshold of SiO2 and multilayer TiO2/SiO2 thin film

Abstract

Laser induced damage threshold (LIDT) of optics is the key point since the time of invention of laser. In this study the LIDT of SiO₂ material which is used with TiO₂ in making higher reflective (HR) coating and antireflective (AR) coating, is explored on the bases of thickness of film and on two different laser wavelengths which lie in Infrared (IR) and visible regions. Samples are deposited by conventional e-beam deposition method having λ/4 and 3λ/4 thickness, of SiO₂ single layer and five layer TiO₂/SiO₂ multilayers with combination of quarter wave optical thickness of each, on BK-7. Annealing of multilayers is done in air at a suitable temperature and its effect on LIDT is measured.  LIDT is measured in Nano-second regime with Nd : YAG laser at 532nm and 1064nm, damage morphology is studied by scanning electron microscope (SEM) and suitable damage mechanism is found out. Optical properties of the films are investigated by spectrophotometer.