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 MgF2, ZrO2 and Al2O3 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.
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.
Silicon is widely used in IR optics, X-Ray optics and electronics applications. These applications require Silicon of
optical quality surface as well as good form accuracy. To get the desired finish and dimensional accuracy, diamond
turning is preferable. Taylor-Hobson Nanoform-250 diamond turning equipment is used to machine flat Silicon mirror.
Negative rake diamond tool is used with a tool nose radius of 1.5 mm. A series of SPDT machining operations are
performed in the sequential combinations of tool feed rate, Spindle Speed and depth of cut. In order to find out the effect
of machining parameters on the Surface Roughness during turning, Response Surface Methodology (RSM) is used and a
prediction model is developed related to average Surface Roughness (Ra) using experimental data. The surface quality is
analyzed in terms of arithmetic roughness (Ra) and Power Spectral Density for uniform evaluation. In addition, a good
agreement between the predicted and measured Surface Roughness is observed.
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 TiO2-Al2O3 and TiO2-SiO2 having different thicknesses for
varied wavelength ranges in the visible region. Three TiO2-SiO2 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 TiO2-Al2O3 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.