Rana, Kiwamu, Lisa, Alexa, Sheila, Evan
We took some time to measure the 1f and 3f DRMI sensing matrices.
To do this, we used the digital lock-in oscillators on the LSC screen to feed back onto some of the DRMI optics (PR2, SRM, BS, and a combination of 1×BS + 0.02×PR2 that we refer to below as BS+PR2).
The procedure was as follows:
cdsutils servo -r LSC-LOCKIN_1_DEMOD_5_Q_OUTPUT -g -10 -s 0 -t 100 LSC-LOCKIN_1_DEMOD_5_PHASE
.z avg -s 8
to average them.Results for the 1f sensing matrix are as follows. The drive amplitudes have been divided out (and the entire matrix normalized).
1f | PR2 | SRM | BS | BS+PR2 |
9I | 2604(2) | 0.136(4) | −51.60(9) | −3.56(2) |
9Q | 107.5(9) | −0.0364(3) | −2.254(15) | −0.035(2) |
45I | 2015(4) | −3.70(4) | −39.69(6) | −5.51(5) |
45Q | −693(7) | −0.469(6) | 29.58(8) | 18.70(5) |
The matrix elements for SRM (in red) are probably bogus, because we were saturating the SRM actuator while driving.
Then we repeated this for the 3f signals, with REFLAIR27I→DEMOD 11, REFLAIR27Q→DEMOD 12, REFLAIR135I→DEMOD 13, and REFLAIR135Q→DEMOD 14. The drive amplitudes were 15, 9333, and 1999 counts for PR2, SRM, and BS. The results are as follows. Again the drive amplitudes have been divided out (and the entire matrix normalized).
3f | PR2 | SRM | BS |
27I | 9400(40) | −2.560(11) | −173.5(3) |
27Q | −154(8) | 0.618(9) | 14.72(5) |
135I | 2940(50) | −7.96(7) | −58.3(5) |
135Q | −22 550(90) | −0.17(7) | 543(2) |
DRMI lost lock before we were able to get the BS+PR2 measurement for 3f.
Kiwamu did some work to figure out what output matrix values are needed to drive mostly MICH; it is 1×BS + 0.02×PR2 − 0.014×SRM. Rana then measured the sensing matrix with 333 counts on MICH, 17 counts on PRM, and 18999 counts on SRM (and without saturation). WFS were engaged, and the loops were notched at the drive frequency (131.7 Hz).
Here is the 1f sensing matrix, with the drives appropriately divided out.
And likewise for 3f.
Also last night, we took similar measurements of the PR2/SR2 portions of the DRMI sensing matrices while we tried bringing in the arms. Sheila started at ≈ 7.5 nm and over a few minutes brought the arms to slightly under 4 nm, at which point we lost lock (the conversion from displacement to detuning is 7 nm / Hzgreen). So the attached plots should be read from left to right.
The big jump at 6.5 nm is because Kiwamu had to tune up the DRMI alignment to prevent lock loss. So the jump in the sening matrix elements isn't surprising. Beyond that, the values appear more or less constant, to within uncertainty.