C-2
C Basics of the Measurement Procedure
C.2 Optical Configuration in the Sensor Head OFV-303/-353
In Polytec’s vibrometers, the velocity and displacement measurement is
carried out using a modified Mach-Zehnder interferometer. The optical
configuration in the sensor head OFV-303/-353 is shown schematically in
.
The light source is a helium neon laser which provides a linear polarized
beam. The polarizing beam splitter BS1 splits the beam into the object beam
and the reference beam.
The object beam passes through the polarizing beam splitter BS2 as well as a
λ
/ 4 plate, is then focused by the lens on the object and scattered back from
there. The polarizing beam splitter BS2 then functions as an optical
directional coupler together with the
λ
/ 4 plate, and deflects the object beam
to the beam splitter BS3. As both arms of the "internal" interferometer are
symmetrical, the optical path difference between the object beam and the
reference beam vanishes within the interferometer. The resulting path
difference is equal to twice the distance between the beam splitter BS2 and
the object.
The Bragg cell in the reference arm of the interferometer generates the
additional frequency offset to determine the sign of the velocity.
The resulting interference signal of the object beam and reference beam is
converted into an electrical signal in the photo detector and subsequently
decoded in the controller.
Figure C.1: Optical configuration of the interferometer in the sensor head OFV-303/-353
B S 1
L e n s
O b j e c t
P r i s m
B r a g g C e l l
B S 3
B S 2
L a s e r
D e t e c t o r
R e f e r e n c e
B e a m
O b j e c t B e a m
l / 4
Summary of Contents for OFV-3001
Page 28: ...3 16 3 First Steps...
Page 54: ...5 12 5 Operating the Vibrometer...
Page 94: ...D 10 D Functional Description of the Controller...
