NAOJ GW Elog Logbook 3.2
Owing to the spurious 17deg of circular retardation observed in BS birefringence characterisitics after correction using Polarization ray tracing, I redid calibration.
1. First it seems the alignment was off by 0.2 cm before the BS. I corrected this using the last steering mirror before the LC path. The beam height is now 7.5cm all along. The alignment was also checked with BS and was slightly(0.1cm) tuned to obtain good alignment in its reflection.
2. The BS is removed. LC voltage changes from 0-3.5V with 0.1V step and 100 avg.
Polarization states without BS:
C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20241004\Fri, Oct 4, 2024 6-35-14 PM.txt
3. The BS is rotated by 180 degrees to measure its back face.
Polarization states after relfection from back side of BS:
C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241006\back_refl\Sun, Oct 6, 2024 5-32-19 PM.txt
The birefringence of BS changed from 17deg to 10 deg after alignment tuning. See the picture for its Jones matrix (Fig1) and birefringence (Fig2). As you can see the JM doesn't have -ve sign any more in the real parts, and is closer to identiy matrix.
The condition on physical realizablity had error bar of 1E-4 (to lower two peaks on BS birefringence).
Polarization ray tracing to correct coordinate systems seems correct. Perhaps can tune BS alignment a bit more.
I made a mistake in measuring the BS. I rotated only 90deg. It was supposed to be rotated by 180 deg.