THORLABS BC207UV, Operating Manual

Page: 161 / 181

BC207 Series
Chapter 9: Application Note
Rev: 8.1, 10-Jan-2022
Page 154
© 2022 Thorlabs
9 Application Note
This chapter contains some background information about the measurement methods of beam
profiles.
Beam profiles can be characterized by a number of different parameters. We aim to offer a
software that allows to measure all usual beam parameters based on ISO11146-1 standard.
In the following sections detailed explanations are given to the measured parameters.
9.1 Ambient Light Correction
Thorlabs Beam Software implements a unique Ambient Light Correction (ALC) method. The
procedure can be started from the Beam Settings panel, topic "
Optical Setup ".
After the laser beam has been blocked and only ambient light enters the sensor, the ALC re-
cords a number of images at different exposure times and averages them. Intermediate values
are interpolated. This allows a precise calculation of the camera's baseline with ambient light
valid at different exposure times.
An outstanding property of the ALC is that the original baseline of the camera (black level) is
corrected for the average intensity of the ambient light "noise". This turns out to be a significant
advantage, particularly for M² measurements - the 4
s values can be determined with a higher
accuracy, as in this case the interference caused by ambient light is nearly eliminated.
9.2 Coordinate Systems
Lab System
The lab system (AKA reference system) of coordinates is based on the true X and Y coordinate
orientation of the CCD camera chip (X = lines, Y = columns).
Transformed System
The transformed system of coordinates is based on the calculated beam axes (minor and major
axes for elliptical fit or for 4
s beam diameter).
9.3 Raw Data Measurements
Lab (or Reference or Sensor) Coordinate System
4 s Beam Width is the width of a beam in X and Y axes (centroids), derived from the second
moment calculation:
where s
x
and s
y
are the standard deviation of the horizontal or vertical marginal distribution, re-
spectively:
and
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