THORLABS M2MS, Operating Manual

Page: 110 / 167

BP209 Series 7 Operation Instructions
Page 108
21424-D02
Astigmatism is known as the effect that the beam waist in X and Y scan direction is not at the
same z position. So there is a difference between the positions of minimal spot diameters z
0y
and z
0y
.
Relative Astigmatism is calculated from the Astigmatism values divided by the mean of the
Rayleigh Length in X and Y.
( )
astigmatism_rel=
_Y _ X
R Y R X
Z - Z
Z Z - ¸
01 01
1 1
2
Full Divergence Angle is explained in section M2 Theory .
Divergence Asymmetry is the ratio of the divergence angles in Y and X axes. Values differing
from 1.0 indicate that the beam ellipticity is changing with Z position, for instance when an ellip-
tical beam is focussed to a round spot.
Note
All results are calculated from the applied fit!
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