Abstract:
Multi-layer Thin-films are the stack of layer of material ranging from fractions of a nanometer
to several micrometer in thickness. Therefore the intensity of light reflected off the surface of
the material and transmitted through the materials can be controlled by optical coating of multilayer thin-film. The design and optimization of such complex structure is heavy problem. At
most achieving the desired optical response from a multi-layer thin-film structure over a broad
range of wavelengths and angles of incidence is challenging and also there is no systematic
method for the design of optical coating but trial and error. The transfer matrix method assisted
by accurate computer calculation allows us to simplify the complexity of the optical function
of thin film. The computer program which calculates the optical functions of multi-layer thinfilm is developed by MATLAB programming language, based on the transfer-matrix method.
By the program developed, anti-reflecting and high reflecting coating was modeled and their
optical functions (reflectance and transmittance) calculated as function of wavelength. The
reference wavelength λ0 = 550nm. In the case of anti-reflecting coating with the thickness
of quarter wavelength (λ 4 0 ) and half wavelength, (λ 2 0 ) layers are arranged in different forms
(quarter-quarter and quarter-half-quarter). The double thin film layer (quarter-quarter) between
the air and substrate, can achieve minimum reflectance and maximum transmittance at only single wavelength (the reference wavelength). The three layer(quarter-half-quarter) films exhibits
slightly greater reflectance (minimum transmittance) at the center of the band and reflectance
is reduced while transmittance is increased, over a much wider wave length range. In the case
of high reflective coating the stack of two (high index and low index) thin film layer with thickness of quarter wavelength (λ 4 0 ) was used. The obtained result indicates that the reflectance
of high reflective coating increases as the number of stacks (layers) added between incidence
medium(air) and substrate(glass) within the stop-band (450nm-700nm) while, the transmittance decreases in this range. The addition of extra layers does not affect the width of the zone
(stop-band) of high reflectance, rather increases the reflectance within it and the number of oscillations outside the zone
