1. Establish a lock of cavity while it is in one of the polarization state (RIGHT/LEFT) created by the 1st QWP. More info on how to lock the cavity (http://hallaweb.jlab.org/compton/OSP/How_to/howto.php?id_procedure=10) To get to either RIGHT/LEFT polarized cavity state, go to "optics table" in epics panel and click lambda/4->Polarization->RIGHT/LEFT. 2. Run the script qwp_scan_onesideR or qwp_scan_onesideL depending on the cavity polarization state located in /home/compton/QW_Plate_Scan/Pol_Test. 3. Now the script rotates the 2nd QWP at the exit of the cavity which is mounted on a stepper motor. It rotates 15 degrees in each step and wait for 40 sec to collect data. Here the wait time is longer, because most likely cavity would lose the lock due to a noise produced by the motor. We want the cavity stay locked while we read the data. We will get 24 data points to finish a full rotation. If during the 40 secs cavity doesn't re-establish a lock, you will be missing a point. If this is a case we have to increase the wait time or improve the cavity tune. So bottom line here is monitor the lock so that we don't get junk data. 4. Analyse the data with FitStokes_Kent2.C script located in the same directory above. 5. Repeat the same steps for the other cavity polarization state. 6. Initialize the 2nd QWP plate to its default position 10625 to the right.
Hope it helps.