THORLABS M2MS, Operating Manual

Page: 13 / 167

BP209 Series 3 Operating Elements
Rev: 8.1, 14-Feb-2022 © 2022 Thorlabs Page 11
3.1.1 Rotation Mount
The BP209 Series Beam Profilers are external optical beam measurement sensors that are de-
signed for free-space applications and come with a rotation mount.
The rotation mount provides up to ± 60° of manual rotation for the X and Y scan axes. Release
the plug on the top and move it to the left or right while keeping the mount fixed - the BP209
Beam Profiler rotates within its outer housing. To arrive at the desired angle use the markers on
the front plate. This way the beam profile can be measured at different directions.
Note
For accurate measurement results make sure the beam enters the input aperture perpendicular
to the front plane and as close as possible to the center of the aperture.
The rotation capability of the sensor with respect to the beam is essential for correct beam el-
lipticity measurements.
Since the major and minor axes of an elliptical beam may have arbitrary position in space, the
scan axes of the Beam Profiler needs to be oriented to these axes in order to measure the real
ellipticity. For the most accurate alignment, it is best to rotate the BP209 while observing the X
and Y
profiles. Determine the point where the profile width in one axis reaches the minimum
and the maximum in the other axis.
Note
Without scan axes alignment the ellipticity measurement may become erroneous!