camilla.compton@LIGO.ORG - posted 11:35, Friday 12 January 2024 (75344)
Improved SQZ SEED polarization. Throughput 30%
Julian, Camilla. WP 11614
With 4mW seed beam injected, we touched the quater and half waveplates in the SEED path on SQZT0 to minimize H1:SQZ-CLF_FIBR_REJECTED_DC_POWER. Plot attached. Reduced HAM7 rejected from 0.32mW to 0.12mW (we've not previously got this to 0 65063).
Throughput to SQZT7 is 1.2mW/4mW = 30%. We expect >40% and we have previously got only get 50%-75% though the fiber coupler switch only (not inc HAM7) 65392 65445.
If we need more power than this we can try to walk the alignment, we tried toughing only one mirror and didn't improve throughput, the second mirror was hard to reach from local laser hazard area.
From ndscope, November 3rd 2022 we had 10.5mW in SQZT7 from 27mW input = 39% throughput.
When we were in HAM6 in September we had removed the fiber switch as it had broken (65063) so it's possible we'll now have ~ half the power we did then.
Images attached to this report
