[Marc, Shalika]

We used our new VI to characterize our LC (previously described in elog 3157 or 3155)

First, we aligned HWP and QWP to read 0+/-0.1 deg ellipticity and 90+/-0.1 deg azimuth angle with our camera.

We installed the LC and rotated it to maximize the ellipticity (-12deg). Note that we expect the LC to not affect the azimuth angle in this configuration but we measured 87.5 deg.

This could mean that our LC axis is not perfectly aligned with our input polarization/camera. We will try to further check this behavior.

In any case we then saved several sets of sweep as in figure 1.

we performed the ellitpticity unwrapping as in figure 2 by flipping twice the ellipticity compared to its maximum value (as expected as we have 2 wrapping points of the ellipticity).

Also note that we had to remove +/-5 points around the end of a sweep which exhibit strange behavior (spikes in ellipticity, azimuth and power).

This could be because the Vrms applied to the LC is quickly change from its maximum to minimum values as we do not see this feature with slow sweep by hand (if I remember correctly).

We measured retardation between 949.9 to 15.7 nm.

The descrepancy with our previous measurements and Thorlabs measurement could be due to this 2.5deg offset in azimuth that might indicate an improper alignment of the LC axis or due to long term fluctuations of the LC response.

Finally, figure 3 reports our 10 sweeps unwrapped.

All these steps are done in Python codes saved in LC-experiment folder.

As the temperature was changing during the measurement, we can see that the main effect is at really low Vrms applied to the LC only.

We plan to further characterize the temperature effect on maximum LC retardation with 0Vrms applied.

Note that one sweep (ie in future corresponding to 250 polarization states) took 25s but this is not limited by VI execution time nor LC.