CC-POL Components: Half Waveplates
Retarder (half waveplate, HWP) modulates incoming radiation such that the polarisation state is rotated by twice the physical rotation of the retarder
- When employed with an analyzer the two vectorial states of polarisation are described
Typical to rotate the HWP to four set angles so that the both vectorial states of polarisation are imaged at each pixel position twice but perpendicular to each other
- Self calibration of the polarimeter is performed during each set of polarisation images, thereby removing effects of array sensitivity to polarisation, flat fielding etc.
Placed as far upstream in beam as possible to minimise number of reflections which lead to instrumental polarisation
Possible drawbacks: reduced throughput, focus change, beam wander, ghosting, lower EE