Sheila, Naoki, Brina, Genevieve

Pump AOM alignment

Today we went to SQZT0 and aligned the pump AOM to get more pump. First we made the ISS drivepoint 0 to get only 0th order beam and maximized its AOM throughput by alignment of AOM. The pump power after AOM was 23mW before alignment and it becomes 37mW after alignment. We also aligned the pump fiber. Although the SHG output power is only 49mW, the pump going to fiber is 31mW and the ISS can be locked with OPO trans of 80. Since the pump power is increased, we adjusted the OPO temperature. The fiber alignment might not be optimized and we will check it soon.

Issue of SHG demod signal

To check if we have mode hop on SQZ laser, we scanned SHG and checked the trans signal. We found no evidence of mode hop, but found the strange behavior of SHG demod signals. We found that the I signal, which is used for SHG lock, is much smaller than Q. We changed the demod phase, but the Q signal is always larger than the I signal.

To use the Q signal for SHG lock, we swapped the I and Q cables and maximized the Q signal by optimizing the demod phase and flipped the sign of servo. Although we should have 10 times larger signal with Q than I, the UGF of SHG with Q signal is around 250 Hz, which is almost the same as I signal. We suspect that the demod board has an issue and we will check it soon.

Finally, we switched back to the nominal I signal for SHG lock. We increased the SHG gain from -11 to 5 to have UGF around 1kHz. The SHG guardian is updated.