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.