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Message ID: 17141     Entry time: Thu Sep 15 16:19:33 2022
Author: Yehonathan 
Type: Update 
Category: LSC 
Subject: POX-POY noise budget 

Doing POX-POY noise measurement as a poor man's FPMI for diagnostic purposes. (Notebook in /opt/rtcds/caltech/c1/Git/40m/measurements/LSC/POX-POY/Noise_Budget.ipynb)

The arms were locked individually using POX11 and POY11. The optical gain was estimated to be by looking at the PDH signal of each arm: the slope was computed by taking the negative peak to positive peak counts and assuming that the arm length change between those peaks is lambda/(2*Finesse), where lambda = 1um and the arm finesse is taken to be 450.

Xarm peak-to-peak counts is ~ 850 while Yarm's is ~ 1100. This gives optical gains of 3.8e11 cts/m and 4.95e11 cts/m respectively.

Next, ETMX actuation TF is measured (attachments 1,2) by exciting C1:LSC-ETMX/Y_EXC and measuring at C1:LSC-X/YARM_IN1_DQ and calibrating with the optical gain.

Using these calibrations I plot the POX-POY (attachment 3) and POX+POY (attachment 4) total noise measurements using two methods:

1. Plotting the calibrated IN and OUT channels of XARM-YARM (blue and orange). Those two curves should cross at the UGF (200Hz in this case).

2. Plotting the calibrated XARM-YARM IN channels times 1-OLTF (black).

The UGF bump can be clearly seen above the true noise in those plots.

However, POX+POY OUT channel looks too high for some reason making the crossing frequency between IN and OUT channels to be ~ 300Hz. Not sure what was going on with this.

Next, I will budget this noise with the individual noise contributions.

Attachment 1: XARM_Actuation_Plot.pdf  19 kB  Uploaded Thu Sep 15 17:21:03 2022  | Hide | Hide all
Attachment 2: YARM_Actuation_Plot.pdf  19 kB  Uploaded Thu Sep 15 17:21:11 2022  | Hide | Hide all
Attachment 3: Sensitivity_Plot_1347315385.pdf  329 kB  Uploaded Thu Sep 15 17:21:19 2022  | Hide | Hide all
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