J. Kissel

Following a similar procedure as was done for the ITMs (see LHO aLOG 14265), I've refined the calibration for the H1 SUS BS optical lever. The new calibrations are
BS P 6.9522 [ct/urad]
BS Y 3.8899 [ct/urad]

They've not yet been installed; will install tomorrow during maintenance.

DETAILS
------------
Currently, the alignment slider calibration gains are 
4.714 [ct/"urad"]
4.268 [ct/"urad"]
based on dead-reckoned knowledge of the actuation chain (see LLO aLOG 5362).

Sheila and Alexa recently found the alignment values for the beam splitter which gets red light onto the ETMY baffle PDs:
            P ["urad"]    Y ["urad"]
ETMY PD1      184.0        -255.0
ETMY PD4      237.1        -287.7
or a displacement of 
BS P    53.12 * 2 = 106.2 ["urad"]
BS Y    23.70 * 2 =  65.4 ["urad"]
where the factor of two comes from the single bounce optical lever effect.

I spoke with Gerardo who informed me that the numbers Keita had posted (LHO aLOG 9087) for the locations of the baffle PDs on the Arm Cavity Baffles are slightly off from reality. He gave me links to D1200296 (ETM) and D1200313 (ITM), which indicate that the PD locations are identical between an ITM and ETM baffle, and are 11.329 [inches] = 0.288 [m] apart in vertical, and 11.313 [inches] = 0.287 [m] apart in horizontal. Again using 3994.5 [m] for the length of the arm (LHO aLOG 11611), and adding 4.847+0.100+0.020+0.200 = 5.167 [m] for the distance between the HR surface of the BS and the back of the CP, through the thin CP, through the ITM QUAD's reaction-to-main chain gap, and through to the HR surface of ITM, respectively (D0901920), that's a lever arm of 3999.7 [m]. Hence, a displacement of
BS P   0.288 [m] / 3999.7 [m] = 72.01 [urad]
BS Y   0.287 [m] / 3999.7 [m] = 71.76 [urad]

The alignment offset slider gains should therefore be corrected by 
BS P  72.01 / 106.2 = 0.67806 [urad/"urad"]
BS Y  71.76 / 65.4  = 1.0972  [urad/"urad"]
or
BS P  1.4748 ["urad"/urad]
BS Y  0.91141 ["urad"/urad]

The new slider gains should therefore be
BS P    4.714 [ct/"urad"] * 1.4748 ["urad"/urad] = 6.9522 [ct/urad]
BS Y    4.268 [ct/"urad"] * 0.9114 ["urad"/urad] = 3.8899 [ct/urad]

We're now storing 4 alignments for the BS, 
                      P ["urad"]       Y  ["urad"]
BS Aligned              210.6             -271.4
   Misaligned           236.5             -287
   To EY ACB PD1        184               -255
   To EY ACB PD4        237.1             -287.7

which should therefore become,

                         P [urad]     Y [urad]
BS Aligned                142.8        -297.3
   Misaligned             160.3        -314.9
   To EY ACB PD1          124.76        160.77
   To EY ACB PD2          160.7         315.66

To do:
- Update calibration in OPTICALIGN gain
- Update calibration in M1 LOCK bank
- Update, confirm, and save corrected alignments
- Capture new safe.snap