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Entry  Thu Jan 22 23:36:50 2009, pete, HowTo, oplevs, arm cavity oplev calibration ETMYpitpower.pngETMYpitcal.png
    Reply  Fri Jan 23 12:48:12 2009, Kakeru, Update, oplevs, arm cavity oplev calibration ITMX_pitch.png
       Reply  Thu Jan 29 17:24:41 2009, Kakeru, Update, oplevs, arm cavity oplev calibration 
          Reply  Sat Mar 14 22:53:12 2009, Kakeru, Update, oplevs, arm cavity oplev calibration oplev.pdf
             Reply  Fri Mar 20 15:37:58 2009, Kakeru, Update, oplevs, arm cavity oplev calibration 
                Reply  Thu Mar 26 09:08:18 2009, Kakeru, Update, oplevs, arm cavity oplev calibration 
Message ID: 1403     Entry time: Sat Mar 14 22:53:12 2009     In reply to: 1259     Reply to this: 1413
Author: Kakeru 
Type: Update 
Category: oplevs 
Subject: arm cavity oplev calibration 
I finished a calibration of optical levers.

To calibrate oplevs, I locked appropriate cavity and tilted a mirror.
A cavity with tilted mirror decrease its arm power. So I can know how much the tilt is.
For calibration of ITMX and ETMX, I locked X arm and measured TRX.
For ETMX, ETMY and BS, I locked Y arm and measured TRY
For PRM, I locked PRC and measured SPOB
For SRM, I locked SRC and measured REFL166

I used, for example, C1:SUS-ITMX_OPLEV_PERROR as an oplev signal.

The calibration factors for each mirror is below. The attachment is figures of my fitting.
I used modified equation for ITM calibration from my last calibration, so the value become small around 30%.

ITMX Pitch: 142   microrad/counts
ITMX Yaw:   145   microrad/counts
ITMY Pitch: 257   microrad/counts
ITMY Yaw:   206   microrad/counts

ETMX Pitch: 318   microrad/counts
ETMX Yaw:   291   microrad/counts
ETMY Pitch: 309   microrad/counts
ETMY Yaw:   299   microrad/counts

BS Pitch:    70.9 microrad/counts
BS Yaw:      96.3 microrad/counts

PRM Pitch:   78.5 microrad/counts
PRM Yaw:     79.9 microrad/counts

SRM Pitch:  191   microrad/counts
SRM Yaw:    146   microrad/counts


It looks strange that ITMY, BS and SRM has different value. I think this is a fitting problem.
These data have some asymmetry and cause these 20%-30% difference.
Actually, PRM Yaw has a little asymmetry but the value doesn't differ from Pitch.
This means that this calibration factor potentially has below 30% error.
(These data are the most fine data. I think we must adjust Y arm yaw alignment. The beam spot of ETMY looks too low!)
For SRM, I couldn't get fine data because it was very sensitive to tilt and easily lose its lock.
When I tuned cavity enough, The data become almost flat, so I used detuned cavity.

It is also strange that ITMX and ITMY is different. I guess that this is caused by the difference of the QPD input. The sum of QPD is around 10000 for ITMX and around 4500 for ITMY.
The difference between BS or PRM and SRM is same, I guess. The sum of QPD input for BS and SRM is around 1500, but for SRM, it is around 10000.

I will write more detailed document and upload it with my calibration code.
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