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Polarisation calibration

For polarisation module calibration, a special double cell containing two dichroic polymer filters (i.e. Polaroid) with their polarising axes orthogonal to each other may be fitted to the carrier. Further cells containing either a calcite or quartz crystal may be used for broader wavelength coverage. There may be some spatial problems if the required crystal thickness is too great. This also applies to the use of two parallel silica plates for partial polarisation.