© 2007-2012 Thorlabs GmbH
77Operating Instruction
It is required to define a Zernike radius because the Zernike functions fitted to the
measured wavefront are normalized to a Unity Radius = 1. Calculated Zernike
coefficients refer to the here defined pupil radius (see Zernike Fit Setup ).
Pupil Diameter (mm)
The here defined Pupil Diameter is twice the normalized radius (= 1) of the Zernike
functions. This Pupil Diameter in mm can be set manually or automatically.
If 'Use Beam Width' is enabled the pupil diameter is automatically adapted to the
measured beam width. The beam width is measured using the second moment
method and corresponds to the 1/e
2
diameter in case of a Gaussian beam shape.
NOTE
The second moment method will calculate accurate beam widths only when ambient
light is shielded from the Wavefront Sensor and the 'Black Level' of the camera is
properly aligned (see Camera Settings Setup ). A positive offset to the beam's
intensity distribution will lead to beam diameters larger than real. A manual defined '
Noise Cut Level' in the Camera Settings will help to reject an increased dark
level.
Let 'Use Beam Width' unchecked to define the pupil size manually. You may define
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