THORLABS M2MS, Руководство по эксплуатации

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BP209 Series 7 Operation Instructions
Rev: 8.1, 14-Feb-2022 © 2022 Thorlabs Page 111
7.2.7.7 M² Troubleshooting
Below are examples of typical problems that may occur and appropriate recommendations for
resolving them.
q
The beam does not hit the sensor at all positions of the stage.
Perform a proper Beam Alignment .
q A timeout occurs during a measurement.
A timeout always occurs when the Beam Profiler does not deliver a valid image within the set
time-out interval. This may be caused by:
·
Saturation of the photo diode. To resolve, decrease incident optical power, or alternatively
use a lens with larger focal length if possible; this will increase the diameter of the focal
spot and in this way lower the focal power density.
· The beam power is too low.
· The beam size is too small and no ellipse could be calculated (if Clip Level Ellipse is se-
lected as beam width). Use a lens with a longer focal length to increase focal beam size.
· The beam is outside the aperture. Align the beam, see section Beam Alignment .
q
M² measurement is carried out, but is displayed, no M² results
Make sure for correct Device Settings .
q
The M² value differs substantially from the expected value.
For example, the beam has a nearly Gaussian intensity distribution and M² values are larger
than 1.1:
·
Check set wavelength (see M² Settings )
·
Check Clip Level of the Calculation Area :
4
If the selected Clip Level is too high, the beam might be cut off and the measured beam
area might be smaller than the actual beam extend. This results in a too small beam
waist and a too small M²
(even below 1).
4
If the selected Clip Level is too low, the Calculation Area and the measurement captures
the beam plus noise around the beam. The measured beam width is then larger than
the actual beam width. This leads to an increased M².
q M² is smaller than 1.0
M² values < 1.0 are non-physical but may be due to
·
A too small Calculation Area (Clip Level too high)
·
The accuracy of the measured result. A error of 5% should be considered.
·
The wavelength setting was not made properly. Set the wavelength to the correct value; M²
results will be corrected without running a new measurement.
q
The beam profile looks distorted (particularly, at the end positions of the stage).
Even if a laser is expected to produce a Gaussian beam with M² = 1.0, the beam still can be in-
fluenced by every optical element between laser and Beam Profiler. For instance, a focusing
lens could be mounted with a tilt or could produce a height distortion which results in optical ab-
errations and reduced beam quality.
Filters and mirrors may impact on the beam profile as well in the case that surfaces are con-
taminated. Clean surfaces according to manufacturer's instructions.
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