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 Tue May 25 17:42:11 2021, Anchal, Paco, Summary, ALS, ALS Single Arm Noise Budget Thu May 27 11:03:15 2021, Anchal, Paco, Summary, ALS, ALS Single Arm Noise Budget Fri May 28 17:32:48 2021, Anchal, Summary, ALS, Single Arm Actuation Calibration with IR ALS Beat Tue Jun 1 16:55:32 2021, Anchal, Paco, Summary, ALS, Single Arm Actuation Calibration with IR ALS Beat Tue Jun 8 11:40:53 2021, Anchal, Paco, Summary, ALS, Single Arm Actuation Calibration with IR ALS Beat Wed Jun 9 18:29:13 2021, Anchal, Paco, Summary, ALS, Check for saturation in ITMX SOS Driver Fri Jul 9 15:39:08 2021, Anchal, Summary, ALS, Single Arm Actuation Calibration with IR ALS Beat [Correction]
Message ID: 16192     Entry time: Tue Jun 8 11:40:53 2021     In reply to: 16171     Reply to this: 16196   16242
 Author: Anchal, Paco Type: Summary Category: ALS Subject: Single Arm Actuation Calibration with IR ALS Beat

We attempted to simulate "oscillator based realtime calibration noise monitoring" in offline analysis with python. This helped us in finding about a factor of sqrt(2) that we were missing earlier in 16171. we measured C1:ALS-BEATX_FINE_PHASE_OUT_HZ_DQ when X-ARM was locked to main laser and Xend green laser was locked to XARM. An excitation signal of amplitude 600 was setn at 619 hz at C1:ITMX_LSC_EXC.

## Signal analysis flow:

• The C1:ALS-BEATX_FINE_PHASE_OUT_HZ_DQ is calibrated to give value of beatntoe frequency in Hz. But we are interested in the fluctuations of this value at the excitation frequency. So the beatnote signal is first high passed with 50 hz cut-off. This value can be reduced a lot more in realtime system. We only took 60s of data and had to remove first 2 seconds for removing transients so we didn't reduce this cut-off further.
• The I and Q demodulated beatntoe signal is combined to get a complex beatnote signal amplitude at excitation frequency.
• This signal is divided by cts amplitude of excitation and multiplied by square of excitation frequency to get calibration factor for ITMX in units of nm/cts/Hz^2.
• The noise spectrum of absolute value of  the calibration factor is plotted in attachment 1, along with its RMS. The calibration factor was detrended linearly so the the DC value was removed before taking the spectrum.
• So Attachment 1 is the spectrum of noise in calibration factor when measured with this method. The shaded region is 15.865% - 84.135% percentile region around the solid median curves.

We got a value of $\frac{7.3 \pm 3.9}{f^2}\, \frac{nm}{cts}$.  The calibration factor in use is from $\frac{7.32}{f^2}$ nm/cts from 13984.

Next steps could be to budget this noise while we setup some way of having this calibration factor generated in realitime using oscillators on a FE model. Calibrating actuation of a single optic in a single arm is easy, so this is a good test setup for getting a noise budget of this calibration method.

 Attachment 1: ITMX_Cal_Noise_Spectrum_1307143423.pdf  368 kB  Uploaded Tue Jun 8 12:53:37 2021
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