Substrate Cleaning Processes and Their Influence on the Laser Resistance of Anti-Reflective Coatings

Abstract

Substrate cleaning prior to coating has a strong influence on the performance of the optical component. Exemplary, none or inadequate cleaning reduces the resistance against laser irradiation drastically. Especially in laser components coated with anti-reflective layers, the interface between substrate and coating is one of the most limiting factors. This study investigates different precision cleaning processes and their influence on the laser resistance of ion-beam sputtered anti-reflective coatings. Therefore, a SiO2/Ta2O5 multilayer anti-reflective coating for a wavelength of 1064 nm and a normal angle of incidence was deposited onto high-quality fused silica substrates. Prior to deposition, the substrates were cleaned with various cleaning processes using different solutions and ultrasonic frequencies. To characterize the cleaned surface quality, the surfaces were analyzed with respect to root-mean-square (RMS) roughness and particle density. Laser damage was measured using a 1064 nm ns-pulsed laser test bench. It was found that an alcoholic pre-clean is recommendable to prevent laser damage caused by organic films remaining from the polishing process. The applied ultrasonic frequencies strongly influenced the particle density down to the sub-micrometer range and in consequence, the laser-induced damage threshold (LIDT). Ultrasonic cleaning at excessive power levels can reduce laser resistance.

Investigation of the Multimechanism Laser Cleaning Dynamics for Rough Fused Silica Surfaces with Organic Contaminants: A Computational Simulation and Atomic Analysis

“…Additionally, an increase in laser energy triggers a more conspicuous thermally influenced region within the material. These discoveries harmonize with the observations documented by Gischkat et al, who highlighted substrate impairment beyond a particular threshold, wherein laser energy densities surpassing 15 J/cm 2 induce damage. Furthermore, elevated energy densities lead to more substantial impairment …”

Fabrication of Robust Paper-Based Electronics by Adapting Conventional Paper Making and Coupling with Wet Laser Writing

“…Initial studies showed that laser writing on filter paper was inefficient presumably because the white filter paper reflects most of the laser energy leading to low photothermal heating. 39 In the specimen at the left in Figure 4a, we repeated laser writing five times over the same area and observed the appearance of the red-colored "SCUT" pattern presumably due to the thermal decomposition of HAuCl 4 . For nanoparticle growth on the seeded filter paper, we placed the specimen in 1% HAuCl 4 solution containing hydroxylammonium chloride (0.2%), a reducing agent, for 30 min.…”

“…As a control, we first wrote this pattern on filter paper (without GO), as illustrated at the left in Figure a. Initial studies showed that laser writing on filter paper was inefficient presumably because the white filter paper reflects most of the laser energy leading to low photothermal heating . In the specimen at the left in Figure a, we repeated laser writing five times over the same area and observed the appearance of the red-colored “SCUT” pattern presumably due to the thermal decomposition of HAuCl 4 .…”