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alexan.staley@LIGO.ORG - posted 15:13, Friday 07 November 2014 (14921)
ETMs L2Angle comparison at 0.33 Hz

(Alexa, Evan, Sheila)

We made a transfer coeffecient measurement of the M0, L1, L3 stages for both of the ETMs so we can make a full comparison of the current confirguration we have. We excited in each LOCK stage at a frequency of 0.33 Hz (with no filters turned on), and took a transfer function of the oplevs in pith and yaw relative to the green arm locking control signal. The results are as follows:

ETMY:

  Pitch (Mag urad/umeter, Phase deg) Y (Mag urad/umeter, Phase deg)
M0 (0.0336, 39.9) (0.004, 164.2)
L1 (0.272, -125.5) (0.0277, 30)
L3 (2.6, -179.6) (0.017,63.1)

ETMX:

  Pitch (Mag urad/umeter, Phase deg) Y (Mag urad/umeter, Phase deg)
M0 (0.20(1), -19(1)) --
L1 (0.5(1), 36(2)) --
L3 (2.9(1), 0(1)) --

Evan found no coherence between his excitations and the yaw oplev which is why those results are empty.

Conclusion: The ESD stage has the worst response for both ETMs in pitch, followed by L1. In Yaw, ETMY L3 and L1 are equally bad. ETMX seems to be worse than ETMY. This is a bit surprising since we only see green transmission drifts in the y-arm when we lock DIFF. One important thing to note is that we do not actuate on L3 at this frequency in ALS DIFF since the crossover between L1 and L3 is around 2 Hz as noted in alog

For reference the templates can be found under: /ligo/home/sheila.dwyer/ALS/HIFOXY/ETMY_L2AngleNov72014.xml and /ligo/home/evan.hall/Public/2014/11/ETMX_L2P.xml  

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