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Entry  Thu Jul 17 00:38:30 2014, Jenne, Update, LSC, RIN in arm transmission TransRIN.pdf
    Reply  Sat Jul 19 17:36:44 2014, Jenne, Update, LSC, RIN in arm transmission TransSqrtInvRIN_vs_ALSsensing_18July2014.pngThorlabsRIN_16July2014.png
       Reply  Sat Jul 19 20:51:51 2014, Koji, Update, LSC, RIN in arm transmission 
          Reply  Wed Jul 23 02:01:15 2014, Jenne, Update, LSC, RIN in arm transmission - revised calibration TransSqrtInvRIN_vs_ALSsensing_18July2014.png
Message ID: 10241     Entry time: Sat Jul 19 17:36:44 2014     In reply to: 10224     Reply to this: 10242
Author: Jenne 
Type: Update 
Category: LSC 
Subject: RIN in arm transmission 

I looked at what the RIN contribution of the sqrtInv sensor is by locking the arms individually on IR using POX and POY.  I then took spectra of the sqrtInv channels.  For the Xarm, I had forced the triggering so that the QPD was being used as the transmission PD, while the Yarm was using the regular Thorlabs PD.  I also had the green lasers locked to the arms, and took beatnote spectra to see what the sensing noise of the beatnotes is, all at the same time.

For the sqrtInv channels, I used the Optickle calibration from elog 10187. For today's plot, I am using the calibration at about 1nm, since that is about where we are when we transition to the sqrtInv Thorlabs signal usually.

For the ALS channel, I was using the _FINE_PHASE_OUT signal, which is in units of degrees of phase for a single green wavelength.  So, since k * x = phi, I want the phase data to be converted to radians (2*pi/360), and use k = 2*pi / lambda_green.  So, doing some algebra, this gives me x = phi_degrees * lambda / 360 for my calibration. 

What I see in the plot is that the ALS sensing noise is pretty bad compared to the sqrtInv channels, so maybe we don't have to work so hard on the ISS this next week.  Also, the Thorlabs PD is much better than the QPDs, which maybe isn't so surprising since we have them set so that they have good SNR at higher power.

Anyhow, here's the plot:


Also, here is the Thorlabs PD only, with single arm locked on RF, with the noise calibrated to different CARM offsets:


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