Optimizing Raman Signal Via Collimator Rotation - THORLABS RSB1 Operation Manual

Raman Spectroscopy Bundle

8.4.1 Optimizing Raman Signal via Collimator Rotation

The starting point of this configuration is the Thorlabs Raman Base Unit RSB1(/M) with front
end RSBC1(/M) as configured at the factory and set up as described in the
laser source fed to the FC/PC port of the RSBC1(/M) via a multimode fiber. In general, excita-
tion light is not completely non-polarized as the original polarization of the laser source is par-
tially preserved even after passage through a considerable length of multimode fiber.
The 90° setup consisting of the RSB1(/M) and the RSBC1(/M) front end only allows observation
of s-polarized Raman scattered light. Therefore, the ratio of parallel and perpendicular compon-
ents contributing to the measured Raman spectrum changes upon rotation of the fiber, in this
case facilitated by the collimator, around the z-axis. As a result, Raman peaks, especially those
corresponding to symmetric vibrational modes, can be strongly enhanced or attenuated via ro-
tation of the collimator on the RSBC1(/M)
the collimator. To do so, carefully loosen the setscrews that fix the collimator in the fiber input
and collimator bundle. The setscrews are marked in the
Note It is not possible to rotate the fiber within the collimator FC/PC fiber port, and thus
fiber rotation around the z-axis can only be achieved by rotating the collimator with the fiber
attached to it.
The next figure
85
panol. Here, the excitation laser was a FPV785M Thorlabs laser guided via its pigtail Æ105mm
multimode fiber at NA=0.22. The excitation power was 250 mW.
Note In the manual above we strongly recommend not using the pigtail of the laser directly,
but use an armored fiber patch cable (see chapter
these measurements we wanted to preserve as much of the laser's polarization and thus
skipped the armored fiber patch cable.
Rev: 1.0, 17-Sep-2021
RSBC1 Fiber Input and Collimator Bundle:
Two small setscrews allow to loosen the
shows the effect of collimator rotation on the Raman spectrum of isopro-
© 2021 Thorlabs
(9 ). This resembles rotation of the fiber attached to
9
following figure
collimator.
Mounting the Laser
Chapter 8: Appendix
manual , and a
17
.
84
) . However, in
22
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