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2003); (Yeh and Gu, 1999); (Wu and Yang, 2001).
The aim of this work is to experimentally and
theoretically investigate the characteristics of the
behavior of light polarization in the liquid crystalline
medium.
2 EXPERIMENT
2.1 Sample Preparation
In order to investigate polarization plane rotation of
light we have prepared cholesteric liquid-crystalline
cell through the contact of two cholesteric liquid
crystals. For that purpose a mixture of right-handed
pelargonium, left-handed oleate and E-7 nematic
liquid crystals was prepared. These two mixtures
were one reflecting in the green range named SG,
the other reflecting in the red range, named SR. One
of the substrates was coated with Cholesteric liquid
crystal (1), which was green in colour, and other
substrate was coated with Cholesteric liquid crystal
(2), which was red in colour. Clearly between two
adjacent surfaces the diffusion process has occurred.
The inner surfaces of glass substrates were first
coated with thin polymide layer and were then
rubbed with a special material. As a result, the
orientation of CLCs director was parallel to the
surfaces, which means that the helix axis was
perpendicular to the surfaces of the cell. The mixture
was drop filled into the empty cell. The thickness of
our sample was 15m.
2.2 Experimental Set-up
In order to investigate the polarization plane rotation
of light we have assembled the experimental set-up,
depicted in Figure 1. The CLC cells were
illuminated He-Ne laser with λ=0.63m and with
λ=0.53m wavelength diode pumping
semiconductor laser radiations.
Before the investigation of the polarization plane
rotation the selective reflection bands for green and
red CLCs were observed.
In order to investigate polarization plane rotation
the primary direction was defined. The angle of
polarization plane rotation was measured every hour
in the temperature range 14-21°C, which includes
selective reflection band gaps of both green and red
CLCs. Measurements were done on the daily basis.
As a source of laser radiation both He-Ne laser and
diode pumping semiconductor laser were used. In
figure 2 dependences of polarization plane rotation
Figure 1: Scheme of experimental set-up for investigation
of polarization plane rotation of light: 1.Source of laser
radiation,2.Prism,3.Polarizer,4.Modulator,5.Microrefrigira
tor,6.CLCcell,7.Polarizer,8.Photodiode,9.Oscillograph,10.
DC source,11.Controller of temperature.
angle on temperature for different cases are
represented
. Figure 2 a) corresponds to the case,
when light from semiconductor laser first falls on a
cell substrate coated with green CLC, and figure 2 b)
corresponds to the case, when substrate of the cell,
coated with red CLC, is illuminated with light from
He-Ne laser. In Figure 2 c) and d) are shown the
following cases: c) substrate of the cell, coated with
green CLC, is illuminated with light from He-Ne
laser, d) substrate of the cell, coated with red CLC,
is illuminated with light from semiconductor laser.
As it is seen from the graphs, the polarization
plane rotation has maximum value in the cases a)
and b) and approximately equals to 35, but the
polarization plane rotates only by a few degrees in
the cases c) and d).
So the main purpose was to obtain large
polarization plane rotation with small loss.
We have also obtained the reflection spectra of
green and red CLCs for the mutual temperature
t=17C .
In order to investigate the transmission and
reflection spectra for unpolarized and linear
polarized lights (at normal incidence) we have
assembled the experimental set-up, depicted in
Figure 3. In our experiment StellarNet spectrometer
with optical resolution of 0,75 nm was used. The
reflection spectra for linear polarized light is
depicted in figure 4.
3 THEORY
3.1 Method of Analysis
The problem is solved by Ambartsumian’s layer
addition modified method. This method was earlier
developed for the solution of astrophysical problems
of multiple scattering in turbid media. It has been
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