Vicky Daniel
Today we swapped the beamsplitter in the squeezer laser path that transmits a sample beam to the IR PD (which monitors the laser power). The old splitter was 98:2 for p-polarization and transmitted about 0.1% in s-polarization. We replaced it with a 98:2 meant for s-polarization that transmitted just shy of 1%. After a turning mirror, another 50:50 splitter was installed. The transmitted beam is used for the IR PD, whereas the reflected beam passes through a half wave plate, a polarizing beam splitter, a quarter and a half waveplate, and two additional turning mirrors into a fiber coupler. The other end of the fiber was connected to the squeezer laser input of the fiber beat note box. We also moved the fiber PSL sample beam from the table feedthrough to the PSL input of the fiber beat note box. This allowed us to lock the TTFSS with the new setup.
A slight realignment was required for the CLF, seed and SHG paths. The power coupled into these fibers came back to near the values where they were.
The channels H1:SQZ-FIBR_TRANS_DC and H1:SQZ_FIBR_REJECTED_DC are now monitoring the power in the fibers of the PSL and squeezer lasers, respectively.
The squeezer laser has been turned off and locked out again after the work was finished.
The power out of the PSL fiber was measured to be 0.925mW. The DC readback of the 1611 then read 785mV. The DC readback is not recorded at the moment. This requires a slow controls software update.
The IR PD had to be recalibrated:
Following the plan in T2300300, here are some photos of the fiber TTFSS path we installed today, with the path and powers labelled and with the path lengths marked, to update H1's SQZT0 optical layout D1201210.
We took the pico waveplates from free-space TTFSS for this fiber TTFSS path, and got the 160 MHz SQZ-PSL beatnote power up to 3.6. In observe, it was ~2, so this beatnote is usable for locking.
To-do later - improve this fiber coupling, currently it is only ~30-40% with some variation between fibers. Moving the lens and collimator +/- 1 inch from design only changed the fiber coupling by a few %, so different lenses might be needed. Can revisit this fiber coupling later.
Currently we have