RAMAN APPLICATIONS IN LIQUID CRYSTALS - Raman Spectroscopy for Soft Matter Applications - page 153

M

Excitation laser

Pol

S

C

PD

P

L NF

Pol

Pol

OF

CL

Amp

Polychromator

FG1

FG2

ICCD

PC Os

Figure 6.12 Schematic drawing of the experimental setup for macroscopic polar-
ized Raman measurement for the analysis of orientational order. The broken lines
represent light streams, and the solid lines represent electric signals. M, mirror; Pol,
polarizer; P, prism; C, sample cell; S, rotating stage; ICCD, intensifi ed CCD camera;
CL, Cassegrain lens; NF, Raman notch fi lter; L, camera lens; OF, optical fi ber; PC,
personal computer; FG1, function generator for the gate pulse; FG2, function genera-
tor for applying the electric fi eld to the sample; Amp, high-speed amplifi er; Os,
oscilloscope.

fi ber and measured by the spectrometer. The change in orientational
order can be measured by the time-resolved measurement. The optical
response can be monitored by detecting the intensity of light passed
through the sample cell.
A Raman microscope improves the spatial resolution of the mea-
surement. The spatial resolution can be increased to submicron resolu-
tion by using a confocal setup. The system is shown in Figure 6.13.

6.6.1 Theoretical Analysis

In order to simplify the theoretical analysis of polarized Raman intensi-
ties and their utilization into orientational parameters measurements,
the following assumption are usually made:

(1) The liquid crystal phase is restricted to nematic or Sm A . The
system is uniaxial so that the molecular distribution is cylindri-