It can be seen in elog 3127 that our polarization camera can only measure polarization ellipticity or retardance between -pi/4 to pi/4.

However, our LC should be able to provide larger retardance meaning that we have to unwrap our retardance measurement.

To reproduce the LC datasheet, we can use the following procedure :

- find the max and min of retardance

- invert all values above the min

- add 90 deg to values below the max (plus a small offset maybe because our LC are uncompensated, here it is -7 deg)

- shift the value below the max compare to the max value using retardance := 2 * retardance_max - retardance

The results for the measurement with various LC temperature is in fig 1.

While the shape and the behavior (smaller retardance with larger temperature) seems correct, we only have about half of the retardance measured by Thorlabs..