daniel.sigg@LIGO.ORG - posted 12:04, Wednesday 13 June 2018 - last comment - 17:40, Wednesday 13 June 2018(42506)
ALS Y laser locking
All PD for ALS Y have been normalized to their new nominal values. The dip in reflection is about 25% (with ~40% expected with perfect mode matching, see alog 42384).
The PLL ugf was verified to be around 25kHz. The PDH servo ugf was set to about 5 kHz. We are able to use 2 100Hz/1kHz boost stages. This is now the default.
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Some plots of our spectra and OLGTFs of the ALS Y PDH. Calibration was done by watching free swinging PDH flashes on an oscope, which was ~500 mV peak to peak, and knowing the green arm pole is now 280 Hz, yielding volts to Hz of 1120 Hz/V. We also rephased the ALS Y PDH error signal by around 25 degrees to align along I-phase. Plot 1 is the In-loop ALS Y PDH error signal ASD. Plot 2 is the estimated ALS Y trans noise contributed from the PDH servo. Simply multiplied the PDH error signal by the new green arm pole. This is more relevant for total ALS Y RMS, which is now around 2 Hz. Plot 3 is the OLG of the ALS Y loop. As Daniel reported, ~ 5 kHz UGF.
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