Reports until 23:42, Thursday 30 October 2014
H1 ISC
evan.hall@LIGO.ORG - posted 23:42, Thursday 30 October 2014 - last comment - 19:16, Friday 31 October 2014(14757)
Measurement of 1f and 3f sensing matrices for DRMI

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:

  1. In the first digital oscillator lock-in matrix, we wired REFLAIR9I→DEMOD 5, REFLAIR9Q→DEMOD 6, REFLAIR45I→DEMOD 7, and REFLAIR45Q→DEMOD 8. Each demod had an 0.1 Hz Butterworth filter.
  2. For each demod, we made all the power appear in I by running, e.g, cdsutils servo -r LSC-LOCKIN_1_DEMOD_5_Q_OUTPUT -g -10 -s 0 -t 100 LSC-LOCKIN_1_DEMOD_5_PHASE.
  3. For each optic in turn, we enabled the oscillator in the output matrix. We then turned on a 131.7 Hz oscillator excitation whose amplitude was 15, 3333, 1999, and 1999 counts for PR2, SRM, BS, and BS+PR2, respectively.
  4. We monitored the four demod I channels in StripTool. Then we used 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.

Comments related to this report
evan.hall@LIGO.ORG - 01:40, Friday 31 October 2014 (14760)
Link

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.

1f MICH PR2 SRM
9I 0.921(26)  1329.0(3.4) 0.04300(70)
9Q 0.1122(58) 76.43(46) -0.02287(16)
45I 0.234(76)  1635.6(3.1) -3.3273(58) 
45Q 20.922(62)  -262.6(5.7) -0.4903(13) 

And likewise for 3f.

3f MICH PR2 SRM
27I 4.32(21)  5410.9(5.8)  -1.7543(47)
27Q 8.431(72) -157.0(2.5)  0.4443(43)
135I -8.5(2.1)  1389.4(22.9) -7.289(59) 
135Q 125.6(2.4)  -12638.3(77.9) -0.135(63) 
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evan.hall@LIGO.ORG - 19:16, Friday 31 October 2014 (14787)
Link

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.

Non-image files attached to this comment