THORLABS RSB1 Operation Manual page 90

Raman Spectroscopy Bundle
scattered light, that is
light is simply not visible in the 90° setup, as it propagates parallel to the observation direction.
This leads to two consequences: First, unless excitation is completely non-polarized, Raman
signals will depend on orientation of the input fiber around the z-axis, and signal strength can
be optimized by rotation of the collimator, which is connected to the fiber (= rotation of the excit-
ation fiber, see section
Second, it appears sufficient to insert a polarizer and a half wave plate into the excitation path
to obtain depolarization ratios of the observed Raman peaks. The polarizer sets linear polariza-
tion, and the half-wave plate allows to switch between s- and p-polarized excitation. Installation
of polarization optics into the excitation path is described in section
in excitation path
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scattered light, as explained in section
Path .
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Note that the situation is different in a 180° (transmission), or in a backscattering setup (e.g. re-
flective front end RSBR1(/M)), where you can also observe p-polarized Raman scattered light.
In this case, the corresponding dipole oscillations are perpendicular to the observation direction
along the z-axis. In a transmission or reflective setup, the Raman signals are not supposed to
depend on orientation of the collimator (or excitation fiber) around the z-axis. In addition, in the
transmission setup all polarities
both excitation as well as Raman scattered light path are installed.
While it is possible to convert the RSBC1 to a 180° setup and observe Raman signal in this
configuration, please note that a significant amount of excitation light will reach the camera
sensor. This leads to increased background and noise levels within the spectral range of the
base unit. Therefore, in the 180° transmission setup, it is recommended to use additional excit-
ation wavelength filtering in the Raman scattered light path, e.g. using
FEL0800 or # FELH0800.
Converting RSBC1(/M) to a 180° setup
1. Turn off the laser.
Warning The excitation laser may be class 3 or even 4 and poses a risk to eyes and skin.
Follow the safety procedures, use safety gear and get in touch with your laser safety officer.
2. Unscrew the excitation fiber by loosening the setscews of the collimator.
3. If connected, disconnect the RSBC1(/M) from the base unit.
4. Unscrew the baffle assembly
5. Remove the protective plate from the CVH100 cuvette holder.
6. Re-mount it opposite to the fiber input and collimator bundle.
Attention Carefully follow laser safety instructions for class 4 laser products when carrying out
any manipulation or modification to any part of the Raman bundle. Keep in mind that a collim-
ated laser beam is emitted from the fiber input of the front end and collimator bundle shown in
the figure below . Always turn off the laser before modifying the setup and work in a secured
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environment after having had consultation with your laser safety person.
Page 83
I I
and . The dipole oscillation of the p-polarized Raman scattered
s-s p-s
Optimize Raman signal via collimator
. It is also possible to install polarization optics into the path of Raman
Polarization Optics in Excitation and Raman Scattering
I I
,
s-s p-s
(2 ) containing the optics for the Raman scattered light path.
9
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, , can be observed, when polarization optics in
p-p s-p
Chapter 8: Appendix
for details).
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Include polarization optics
Thorlabs item #
MTN022733-D02