[Marc, Shalika]

When we measured the polarization state with the polarization camera directly after the LC we could see that the azimuth angle seems to change a lot around the half-wave retardation voltage.

We tried to measure the fast axis direction by minimizing the transmitted power of the LC after a polarizer but the results were quite strange and not so consistent when repeated..

One possible explanation is that the power minimization was not precise enough to do by hand.

We decided to follow the procedure of [1] where we installed the output polarizer to be in cross-polarizer configuration and measured the transmitted power while appling a sawtooth voltage and rotating the LC from 0 to 360 deg with 10deg increment.

The resulting function is fitted for a given voltage by a sum of cosine with different orders, all as a function of (x-x0) where x is the rotation angle of the LC and x0 a possibly voltage-dependent offset that should correspond to the LC fast axis rotation as a function of the applied voltage.

By repeating this for every voltage we can get the attached figure where we found that the fast axis orientation is almost voltage independent (within 1deg).

[1] : Measurements of linear diattenuation and linear retardance spectra with a rotating sample spectropolarimeter David B. Chenault and Russell A. Chipman