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26 WFS Series

The image is scanned for detectable spots generated by the microlenses and their

positions are compared to reference positions. The user select an internal or an user

reference table of spot positions.

Spot deviations are calculated and afterwards integrated in order to get a wavefront

array which is displayed in a 3D diagram. All valid spot deviations within the defined

pupil region and the desired number of Zernike orders / modes are input data to the

Zernike fit that fits the measured wavefront using well-known Zernike functions.

Output data are Zernike coefficients which are displayed numerically and within a

bar graph panel. All or a few selected Zernike modes are used for the wavefront

reconstruction. Also the difference between measured and fitted wavefront data is

available.

3.1

Shack-Hartmann Functional Principle

The WFS series Wavefront Sensor consists basically of a CCD/CMOS camera with

a microlens array mounted in a defined distance in front of its sensor chip. Each

microlens generates a spot onto the sensor whereas the spot centroid position

depends on the wavefront gradient in front of the lens area.

Each microlens of the lenslet array collects the light falling onto its aperture and

generates a single spot on the detector plane (CCD/CMOS camera) that is situated

a focal length behind the lenslets. The spot positions are straight behind the lenses

only in case the launched wavefront is plane and parallel to the plane of the lenslets.

We call these the Reference Spot Positions or reference spotfield.

In the common case however, the current spot positions will be deviated in X and Y

direction, that is, every spot lies away from the optical axis z of its associated

microlens, separated by an angle

THORLABS WFS Series User Manual

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