THORLABS BC207UV, Operating Manual

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BC207 Series Chapter 6: Operation Instructions
Page 123
MTN026962-D02
6.3.8 Divergence Measurement
The Divergence Measurement calculates the divergence angle of an unfocused convergent or
divergent beam by measuring the beam diameter at different points along the beam propaga-
tion axis. A linear fit is applied to the measured data.
The measurement technique is very similar to the Beam Quality (M²) measurement, thus the
same hardware can be used with exception of the focusing lens.
The Divergence Measurement is part of the Beam Quality measurement tool and uses the
M2MS extension as well.
Please open the M2 measurement panel via the icon to arrive at the alignment and diver-
gence measurement GUI.
To prepare for and perform a divergence measurement, please deselect the icon on the left
side of the window. This will switch the interface to the divergence measurement window.
6.3.8.1 Beam Alignment
Why Beam Alignment?
The Beam Profiler has a defined input aperture, so when moving the translation stage it must
be ensured that the laser beam remains within the aperture. Ideally, the beam centroid remains
centered within the aperture during movement of the stage - this is a precondition for correct
beam quality measurements.
The M2MS Measurement System is factory aligned. A beam that enters the M2MS exactly
parallel to the stage movement direction will remain centered to the Beam Profiler aperture
during stage movement. In other words, the beam alignment is dependent only on the position
of the light source. In most cases the light source is a device with open beam output. In order to
direct the beam under test into the M2MS, a combination of two adjustable mirrors is required,
Thorlabs offers a variety of such items.
The beam alignment is executed in 2 steps, guided by a software wizard:
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