THORLABS BC207UV, Operating Manual

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BC207 Series Chapter 9: Application Note
Page 155
MTN026962-D02
Note
The 4
s
Beam Width measurement is not in conformity with ISO11146! In accordance with
ISO11146-3, beam diameters shall be defined at a 1/e² clip level for Slit Beam Profilers, while
for Camera Beam Profilers the 4
s X' and 4 s Y' beam widths apply.
Transformed Coordinate system
According to ISO11146-1, the second moment beam widths are calculated in the transformed
coordinate system that follows the elliptical fit (4
s X' and 4 s Y' beam width). Here, the following
formulas are used:
where the coefficient
The azimuthal angle is calculated by the formula
According to ISO11146-1, if the ellipticity is larger than 0.87, the beam profile may be con-
sidered to be of circular symmetry at that measuring location. In this case, ISO11146-1 allows
the calculation of only one common 4
s
beam width (4
s
simplified).
Beam Diameter (4 s simplified) is the diameter derived from the second moment calculation
on radial distance (pixel-centroid):
Effective Beam Diameter is the diameter of an equivalent circular beam area, within which the
pixel intensities are above a level X (in per cent of the peak intensity = clip level):
with
N number of pixels with intensities above clip level
A
pix
pixel size (for BC207 = 3.45*3.45µm²)
Peak Position
X, Y : position of the pixel with highest intensity (AD value) which is found first with respect to
reference position.
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