THORLABS WFS20-14AR, Operation Manual

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Wavefront Sensor
Pupil Diameter (mm)
The Pupil Diameter as set here 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 automati-
cally adapted to the measured beam width. The beam width is measured using the second mo-
ment method and corresponds to the 1/e2 diameter in case of a Gaussian beam shape.
Note
The second moment method will calculate accurate beam widths only in the case that ambient
light is shielded from the Wavefront Sensor and the
Black Level of the camera is aligned prop-
erly (see Camera Settings ). A positive offset to the beam intensity distribution will lead to
beam diameters larger than real. A manually defined Noise Cut Level in the Camera Set-
tings is helpful to compensate an increased dark level.
Disable Use Beam Width if the pupil size should be set manually. An elliptical pupil can be set
up by entering different values for X and Y diameter. In this case, the geometric mean of the el-
lipse dimensions defines the diameter of the Zernike circle, and for Zernike calculations the el-
liptical beam is scaled to fit and fill the dimensions of that circle.
Note
The option Use Beam Width must be switched off before operating the WFS20 instruments in
High-Speed Mode, because the beam width cannot be measured with a sufficient accuracy in
High-Speed Mode.
Note
The pupil diameter must be smaller than the active camera area as defined by Camera Image
Size setting (see Camera Settings ), otherwise the warning "Pupil is larger than selected
camera area" will occur (see section Measurement Warnings and Errors ). This requirement
prevents Zernike calculation errors that would occur if the pupil included regions with no meas-
urement data points (lenslet focal spots).
See section Minimal Beam and Pupil Diameter for the minimal pupil diameter that is required
for calculation of Zernike modes up to a desired order.
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