Open AccessMulti-layer Laser Mirrors for Optical Sensors Deposited by Electron Beam Deposition and Ion Assisted Electron Beam Deposition
Author(s) -
Laxminarayana Gangalakurti,
K. Venugopal Reddy,
Inder Mohan Chhabra
Publication year - 2021
Publication title -
international journal of engineering and advanced technology
Language(s) - English
Resource type - Journals
ISSN - 2249-8958
DOI - 10.35940/ijeat.c2153.0210321
Subject(s) - materials science , optics , coating , optical coating , ion beam , thin film , surface roughness , optoelectronics , laser , layer (electronics) , beam (structure) , nanotechnology , composite material , physics
High reflectivity and low loss mirrors are very much essential for state-of art sensors like Ring Laser Gyroscopes widely used for navigation of moving platforms. Surface scattering is the main source of loss for the Laser mirrors of high reflectivity. Surface scattering also lead to coupling of back reflected light leading to dead band of optical sensors at low input rotation. Super polished glass substrates have been prepared from low expansion glass ceramic material. Surface roughness is achieved about 3-5Å (RMS value) for the ceramic glass substrates prior to thin film coating. The substrates are deposited with 41 alternative layers of SiO2 and Ta2O5 of Quarter-Wave optical thickness with Electron Beam Deposition (EBD) technique. Ion beam Assisted Electron Beam Deposition (IAEBD) is used for another batch of substrates to coat identical stack of layers on glass substrates of the same surface quality. The key process parameters of both the coating processes are presented. The optical constants of the films are evaluated with spectroscopic Ellipsometer from 400nm to 1600nm. Total Integrated Scattering is estimated from the achieved surface finishing of mirrors deposited. The multi-layer coatings are characterized with UV-Vis-IR Spectrophotometer and Cavity Ring Down(CRD) loss meter. The quantitative optical loss of the mirrors is measured at 45o angle of incidence with CRD loss meter. The merits of ion assisted EB process over simple EB coating processes are evaluated against optical constants of thin films and performances of mirrors. Fitness of the processes for realizing Laser mirrors for optical sensors at 632.8nm is evaluated.