We show the results obtained following the last report (06 November 2020).
1. Similarly to the polarizer at the input of the rotator, we initially tested the polarizer (pol_out), obtaining the following results:
-with p polarization, we measured in reflection from the pol_out
Rp1≈30 μW Rp2≈60 μW
so we have losses of less than 0.1%;
-with s polarization, we measured in transmission to pol_out Ts≈5 μW
so we have an extinction of about 46 dB.
2. We placed pol_out at the output of the rotator at Brewster's angle (bottom coating) and we placed the motorized HWP and we tuned it so that the pol_out reflections were minimized (220μW).
It is important that the FI is well aligned with the incident beam in order to obtain good losses and good extinction.
- We then measured a power in reflection back to the FI equal to (with incident power before calcite of 243mW and after of 216mW):
P_back≈7 μW,
which corresponds to an extinction of about 40.5 dB.
- We then measured the losses due to each optic that makes up the FI:
pol_in reflections= 90μW, pol_out reflections=220 μW, TGG reflections=130 μW, theoretical absorption of TGG=2400ppm
and we have also minimized the HWP reflections.
We therefore get losses due to the optics of the FI around 0.5%.
3. As further confirmation of the losses due to the FI, we measure the power before and after the FI.
For greater precision, we fixed the power meter in one position and took measurements with and without FI, also looking for the optimal alignment of it.
We also took into account the fluctuations due to the instability of the power measurement due to the laser itself; after taking several values, we get average losses of 0.7%.
4. The FI is ready to be installed on ESQB1.
Photo attached.
