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Entry  Mon Apr 14 19:02:09 2014, Jenne, Update, LSC, MICH gets noisy as CARM or DARM offset reduced MICH_fuzzy_when_offsets_small_longerData.pngTRX_TRY_100cts.pngMICH_fuzzy_when_offsets_small.png
    Reply  Tue Apr 15 09:32:19 2014, Gabriele, Update, LSC, MICH gets noisy as CARM or DARM offset reduced 
Message ID: 9813     Entry time: Tue Apr 15 09:32:19 2014     In reply to: 9809
Author: Gabriele 
Type: Update 
Category: LSC 
Subject: MICH gets noisy as CARM or DARM offset reduced 

I guess this is normal. DARM has (almost) the same effect of MICH on the corner interferometer signals, just increased in amplitude by the arm cavity amplification. When the arm is out of resonance, DARM is almost completely depressed and it is not affecting MICH at all. On the other hand, when the cavities are exactly at resonance, DARM signal is amplified w.r.t. MICH by the cavity gain (2F/pi).

Since DARM is still controlled with ALS, it is probably noisy. The closer to resonance you move the cavities, the more ALS noise in DARM will affect MICH.


Quote:

When looking at the data, I see that the MICH error signal gets fuzzier when the arms get close to resonance. (Note here that because I forgot to zero the carm offset before finding the resonances, -3 is my zero point for this plot and the next.) 

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