Matteo, Simon

Yesterday, we finished to restart the translation stage after the power outage the day before.

After making sure that everything is working properly, we started to reconfigure the PCI bench for the polarization measurements:

• placing ND-filters in the beam-path before the shutter (-> order ~ 2)
• placing a Vantablack beam-dump at the same area to cover the ND-filter reflection
• putting a PBS after the first lens of the telescope
• putting a QWP  and a HWP after the PBS
• placing a razor beam-dump before the second lens of the telescope to cover a ghost-beam coming from the ND-filters
• putting a 1" lens (f=150mm) together with a beam-tube on the detector stage
• putting a second PBS so that the beam-focus is ~ 2 cm behind the PBS
• placing a beam-dumb behind the blind-side of the PBS to cover back-scattering
• putting each a PSD (position sensitive detector) 2 cm behind the S-pol and P-pol side of the PBS
• Connecting the PSDs to the Lock-Ins and fine-tune the position of the PSDs with an oscilloscope (use the sum-output for the Lock-Ins and the X/Y output for the fine-tuning; beam should be centered)

After the setup is done, we calibrated the QWP and HWP in an iterative manner to produce a maximum in P-pol.
The data on the calibration are as follows:
S-pol PSD maximum voltage: 285 mV
S-pol PSD minimum voltage: 0.77 mV

P-pol PSD maximum voltage: 349 mV
P-pol PSD minimum voltage: 0.2 mV

That is comparable to what we got before.

(Note, that these number might be imrovable as we didn't spent so much time in adjusting the PBS position.)

We started a map of the Shinkosha TAMA#2 sample during the night. The results can be seen from the attached figures.
The polarization is relatively homogeneous. However, there are two main areas with different polarization-angles on two sides which leaves the center of the sample with the largest gradient in the polarization angle.
It is noteworthy that the distribution of polarization angles remembers a little bit on the 3-fold splitting visible in the absorption maps (see the elog entry 1633).