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PAX1000
5 Operating Instruction
5.1 Alignment Assistance
For accurate measurements, it is essential to align the incident beam so that it is centered in
the input aperture and is normally incident on the rotating l/4 waveplate.
The beam centering is particularly important in the case of large incident beam diameters, close
to the aperture diameter ( Ø 3.0 mm). In such cases the correct centering is essential to avoid
beam cutting and reflections from the inner surface of the hollow shaft that holds the waveplate.
The beam centering can be achieved by using the protection cap with engraved cross-hair
(PAX1000VIS) or with a viewing target (PAX1000IR1 and ~IR2).
The angular alignment is critical for another reason: As explained in the section Rotating Wave-
plate Technique , the photo current is analyzed by a Fast Fourier Transformation and ideally
consists only of even-numbered components (harmonics). If the beam hits the waveplate not
exactly perpendicular, unwanted odd-numbered harmonics will appear in the photo current. The
same happens, if the incident beam consists reflected from the inner surface of the hollow shaft
light components. These unwanted components have a significant impact on the measurement
accuracy. The Alignment Assistance tool can be used to align the beam, which will minimize
the contribution from unwanted components.
Click the icon in the Tools ribbon. A new screen comes up.
The Alignment graph shows the fraction of wanted components in the photo current. The green
portion of the scale defines the range of acceptable alignment values. Click the Start Alignment
button.
Adjust the alignment of the beam with respect the PAX1000 beam. When the best alignment is
achieved, click Stop Alignment and close the window.
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