Reports until 13:58, Monday 23 December 2013
H1 ISC
keita.kawabe@LIGO.ORG - posted 13:58, Monday 23 December 2013 - last comment - 09:49, Tuesday 07 January 2014(9064)
Green beam finding in X arm (Daniel, Keita)

Summary: Green injection hits the center of ITMX, comes back to the center of ETMX, and then back again to the center of ITMX. The alignment is good, with one caveat that HEPI should be tilted significantly in  PIT to help TMS. Since EX PIT is unaffected by the HEPI, we're using EX sus bias to point it down by 330 urad.

1. Green beam from TMSX to ITMY

After Kyle opened the GVs we started scanning TMS to find the green beam on ITMX baffle diodes. Somehow PD4 amplifier was busted so we reconnected PD4 to PD3  amplifier.

At first TMSX was pointing up too much, and I had to give HEPI a PIT (RY) offset of -12000 counts to H1:HPI-ETMX_BLND_IPS_RY_OFFSET with a gain of 1. HEPI loops were all open, so that just gave a DC offset to the HEPI angle. After that treatment, we were able to maximize the output of three baffle diodes using the following offsets for TMS bias:

  Center =(PD1+PD4)/2 PD1 PD2 PD4
H1:SUS-TMSX_M1_OPTICALIGN_P_OFFSET 152.5 118 53 187
H1:SUS-TMSX_M1_OPTICALIGN_Y_OFFSET -221.5 -190 -256 -253

See E1300634, figures 12 and 13, for the diode layout. PD1 and PD4 are two diagonal ones around the baffle hole, PD2 and PD3 are far from the mirror. "Center" is the mean of PD1 and PD4 and should be close to the real center of the optic.

Baffle diode channel names are H1:AOS-ITMX_BAFFLEPD_1_POWER etc., but they are not trended as of now. Also note that H1:AOS-ITMX_BAFFLEPD_3_POWER is actually reading PD4.

Transimpedance for the PDs were set to 20 kOhm, and when maximized the outputs were about 2.5V for PD2 and PD3, and about 2.3V for PD1.

Comments related to this report
keita.kawabe@LIGO.ORG - 16:34, Monday 23 December 2013 (9071)
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2: ITMX reflection on ETMX

Got the beam reflected off of ITMX on ETMX baffle diodes. We used a factor of 10 larger trans impedance (200kOhm). All diodes worked and the channel numbering made sense.  H1:AOS-ETMX_BAFFLEPD_1_POWER= ETMX baffle PD1 etc.

  Center PD1 PD2 PD3 PD4
H1:SUS-ITMX_M0_OPTICALIGN_P_OFFSET 82.8 66.6 36 65.6 99
H1:SUS-ITMX_M0_OPTICALIGN_Y_OFFSET -55.5 -72.9 -41 -8.9 -38

Despite 10x higher trans impedance the maximum we got was something like 6V (VS 2.5V), so it's like a factor of 4 reduction. Probably the mode matching into the arm is not good.

keita.kawabe@LIGO.ORG - 16:53, Monday 23 December 2013 (9072)
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3: ETMX reflection back to ITMX

I had to tilt the ETMX significantly in PIT, but anyway.

  Center PD1 PD2 PD4
H1:SUS-ETMX_M0_OPTICALIGN_P_OFFSET 332.5

310

 290 355
H1:SUS-ETMX_M0_OPTICALIGN_Y_OFFSET

-3.75

 26.5 -10 -34

Transimpedance is again 20kOhm and the maximum was about 0.3V, so it's a factor of 2 reduction in power (VS 6V 200kOhm ETM diodes).

At this point I had a power back in REFL B diode, and saw a fringing, but after 5 minutes the fringing was gone. Either the alignment is drifting (turns out that the ISI was undamped), or the frequency noise is too large (couldn't lock PLL).

During this operation I tripped ETMX watchdog, HEPI was restored after that but I forgot about ISI. That is OK, it's just that ISI was undamped.

keita.kawabe@LIGO.ORG - 17:11, Monday 23 December 2013 (9073)
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4. ETMX initial alignment implication

The above shows clearly that, without any suspension slider bias, ETMX is pointing up 330 urad.

This should be either the initial alignment (we dead reckoned 300 urad caused by the weight of first contact) or the optic drifted after pumping down, but the former is more likely.

keita.kawabe@LIGO.ORG - 09:49, Tuesday 07 January 2014 (9132)
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