A single-layer SiO2 film is deposited using ion-assisted electron beam evaporation technique, and the deposited film is characterized using variable angle spectroscopic ellipsometry, UV–Vis–NIR spectrophotometer, coherence correlation interferometer, and Abbe refractometer as well as image processing techniques to investigate its optical and surface properties. The surface quality of the film in terms of average roughness, kurtosis, skewness, and power spectral density (PSD) is analyzed using interferometer and image processing. The refractive index of the SiO2 film is found to increase from 1.452 to 1.482 at 550 nm with increase in film thickness. This is corroborated by Abbe refractometer findings where the film refractive index is found to be 1.46490 and 1.48226 for a film thickness of 100 and 400 nm, respectively. The SiO2 film also results in reduction in average surface roughness from 35 nm of the uncoated substrate to 0.15 nm of the coated surface. Statistical indicators of surface quality extract from interferometric images such as kurtosis, skewness, and PSD and also exhibit sharp decline in their respective values of the coated surface as compared to the uncoated substrate indicating improvement in the surface quality after coating.
Rugate filters are a special kind of graded-index films that may provide advantages in both, optical performance and
mechanical properties of the optical coatings. In this work, design and optimization of a high reflection rugate filter
having reflection peak at 540nm has been presented which has been further optimized for side-lobe suppression. A
suitable number of apodization and matching layers, generated through Quintic function, were added to the basic
sinusoidal refractive index profile to achieve high reflectance of around 80% in the rejection window for normal
incidence. Smaller index contrast between successive layers in the present design leads to less residual stress in the thinfilm
stack which enhances the adhesion and mechanical strength of the filter. The optimized results show excellent side
lobe suppression achieved around the stopband.
Broadband Multilayer Antireflection (AR) coatings markedly improve the transmission efficiency of any optical
component such as lens, prism, beam-splitter, beam combiner or a window. By reducing surface reflections over a wide
wavelength range, broadband antireflection coatings improve transmission and enhance contrast which is desired in
avionic displays. The broadband antireflection coating consisting of MgF<sub>2</sub>, ZrO<sub>2</sub> and Al2O<sub>3</sub> were designed to cover the
whole visible spectrum and fabricated on optical grade glass substrate. The optical characterization of these coatings
indicates reduction of the reflection to 2.28% as compared to 8.5 % at 545 nm (i.e. design wavelength of most avionic
displays) for bare substrate making them useful in optical displays for avionic applications.
Multi-layer reflective thin film filters optimized for oblique incidence angles were deposited on glass substrates using
Electron Beam evaporation technique with in situ thickness monitoring. The present study involves deposition and
optical characterization of 5 layered multi-layer structures of TiO<sub>2</sub>-Al2O<sub>3</sub> and TiO<sub>2</sub>-SiO<sub>2</sub> having different thicknesses for
varied wavelength ranges in the visible region. Three TiO<sub>2</sub>-SiO<sub>2</sub> multi-layer thin film filters were deposited having peak
reflectance at 480 nm, 540 nm and 675 nm respectively corresponding to light sources in the blue, green and red
wavelength regions. Similarly, a TiO<sub>2</sub>-Al2O<sub>3</sub> multi-layer was fabricated having peak reflectance of around 64% at
610nm. These filters were deposited at an elevated temperature of 250° C in an oxygenated reactive environment for
better adhesion, mechanical strength and proper stoichiometry. Reflectance measurements of these multi-layer filters at
oblique incidence angles reveal high reflectance of around 70 ~ 75% with a reasonably broad reflection band which can
have wide applications in beam steering, shaping and folding applications in various complex optical systems facing
constrained space and weight requirements.