Application Note Polarization Dependent Raman Spectroscopy - THORLABS RSB1 Operation Manual

Raman Spectroscopy Bundle

8.4 Application Note Polarization Dependent Raman Spectroscopy

Raman signal is a technique for the chemical identification of substances based on material-
specific spectral distribution of Raman peaks (molecular fingerprint). In many cases, controlling
polarization of excitation light as well as polarization in the observation path of Raman scattered
light adds valuable information, such as information on the symmetry of bond vibrations.
The comparison of Raman spectra with parallel and perpendicular polarization of excitation with
respect to the observed Raman scattered light allows for the investigation of the symmetry of
bond vibrations within a molecule. Considering a particular peak in the Raman spectrum, the
symmetry of the bond vibration behind this peak is characterized via the depolarization ratio:
Here, I and I are the Raman peak intensities for parallel and perpendicular polarization of the
^ ||
observed Raman scattered light with respect to excitation light. The respective components in
the Raman scattered light are denoted as parallel or perpendicular components. A vibrational
mode is completely symmetric, and referred to as a polarized band, if r < 0.75. In contrast, a vi-
brational mode of r ³ 0.75 is not completely symmetric and is called a depolarized band.
This application note describes how to use the Thorlabs Raman bundle to investigate polariza-
tion dependent Raman scattering.
Polarization Dependent Raman Spectroscopy Using the Thorlabs Raman Bundle with the
Cuvette Front End RSBC1(/M)
In this application note, all directions are according to the coordinate system shown in the
sketch below . Excitation light propagates along the z-axis, s-polarized means polarization in
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the y-direction, the p-polarized means polarization in the x-direction. In general, there are four
combinations for polarization of excitation with respect to Raman scattered light, resulting in
I
Raman signals ,
s-s
I I
= =
.
s s-p
^
Description of the below quoted orientation
As the direction of observation is along the x-axis with the RSBC1(/M) in as-delivered condition
(90° setup, see left side of the figure
Rev: 1.0, 17-Sep-2021
I I I
, , In isotropic samples, like normal liquids,
.
p-s p-p s-p
© 2021 Thorlabs
Ι
P
r
=
Ι
^
above ) we can only observe s-polarized Raman
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Chapter 8: Appendix
I I I I
= = , and
s-s p-p p-
||
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