lisa.barsotti@LIGO.ORG - posted 23:27, Tuesday 04 November 2014 - last comment - 14:47, Thursday 06 November 2014(14855)
Good DRMI times
Evan, Sheila, Nic, Lisa To answer Peter's questions , we have relocked the DRMI (without arms) on 1f and 3f (10W input power, 27 mW on the BBPD photo-detector). The DRMI was very stable in both cases, here are the good times: Nov 5, 6:00 - 6:15 UTC DRMI locked on 1f, WFS on Nov 5, 6:30 - 6:45 UTC DRMI locked on 3f, WFS on Evan is about to post plots with error signal spectra. It is probably a good idea to make some plots with ground motion/ISI/optical lever signals to "capture" these good times.
These are the corresponding RFPD spectra. The analogous LLO measurement is LLO#15430. LLO's measurement of RF135 seems pretty surprising, since the 3f demodulated spectra appear to be almost entirely noise-dominated above 20 Hz.
What's this 2449.25Hz line that grows over time?
In the attached left, the error signal for PRCL and SRCL grew larger and larger toward the end of the lock.
In the attached right, red, blue and green correspond to the end, middle and the beginning of the lock. The difference in noise floor might be that they were switching from 1f and 3f or vice versa.
Regardless, a line at 2449.25Hz grew larger over time and it was dominating the error signal RMS.
Is this something intentional? Oscillation somewhere? Rogue line?
I am not sure what the 2449.25 Hz line is; there is not a line there that I know of...
In terms of the difference in the noise floor, I can confirm that this comes from the 1f to 3f transition. Keita's green trace was taken from 5:50 PM UTC, blue trace from just after 6:20 PM UTC, and red trace was taken at 6:50 PM UTC. I have attached a dataviewer snap shot showing the LSC PD input matrix of the MICH (2_23), PRCL (3_20), SRCL (4_22) 3f signals around that time. The MICH and PRCL signal transistion at around 6:17 PM UTC, which explains why the blue and red traces in those plots go up. Meanwhile, SRCL transitions a bit later at 6:26 PM UTC, which explains why only the red trace goes up in the noise floor.
According to Dennis the lowest elastic mode of the beamsplitter is expected to be at 2458 Hz (right circular cylindrical without wedge angle, bevels, wire standoff-prisms).