THORLABS WFS20-14AR, Operation Manual

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Wavefront Sensor
Note
The accuracy of the calibration increases if image averaging is set to > 1, see Camera Settings
Setup panel.
The generated user calibration data are only valid for the actual MLA and camera image size,
that are selected in the
Camera Settings Setup and Wavefront Setup panel. Switching to
an other MLA or camera resolution will require a new calibration!
If the ' User Calibration ' option is enabled, the stored file for a particular camera, MLA, and res-
olution is automatically loaded at program start and every time the camera resolution or MLA is
changed.
5.2.1.4.1 Spherical Wavefront
User Calibration using a Spherical Wavefront
In order to perform a spherical wavefront user calibration you need to apply a high-quality diver-
gent beam that originates from a point source with a perfect spherical wavefront. A single-mode
fiber output without any collimators or lenses is ideally suited for that purpose. Be sure the
beam is properly aligned to the Wavefront Sensor and fills the selected active camera area
completely.
Note
The calibration fails for insufficiently illuminated regions of the camera sensor. Although no er-
ror occurs, the corresponding area will be excluded from further wavefront measurements.
1. Select the Internal Reference in the Wavefront Sensor Setup Panel :
2. Adjust the point source so that it is centered in front of the Wavefront Sensor at a distance in
the range 100 mm to a maximum of 5 m.
Note The geater the distance between the point source and the WFS, the lower the
curvature of the wavefront. In other words, the spot displacements decrease and the meas-
urement of the wavefront curvature becomes more sensitive to noise and ambient light. In
addition, the power density on the CMOS sensors drops with the square of distance, which
also increases the impact of noise sensitivity on the measurement. For these reasons, it is
recommended that the distance to the source not exceed 500 mm.
The Radius of Curvature (RoC) is calculated and displayed by the WFS software. Assuming
a point source and propagation in air, the RoC is equivalent to the distance between the
camera sensor and the light source.
3. Start the calibration procedure using Menu
à
Calibration
à
Spherical Wavefront or
simply click on the appropriate symbol in the toolbar. The dialog window illustrates the re-
quired calibration setup:
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