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Message ID: 15650     Entry time: Thu Oct 29 09:50:12 2020
 Author: anchal Type: Summary Category: Calibration Subject: Preliminary calibration measurement taken

I went to 40m yesterday at around 2:30 pm and Koji showed me how to acquire lock in different arms and for different lasers. Finally, we took a preliminary measurement of shaking the ETMX at some discrete frequencies and looking at the beatnote frequency spectrum of X-end laser's fiber-coupled IR and Main laser's IR pick-off.

### Basic controls and measurement 101 at 40m

• I learned a few things from Koji about how to align the cavity mirrors for green laser or IR laser.
• I learned how to use ASS and how to align the green end laser to the cavity. I also found out about the window at ETMX chamber where we can directly see the cavity mode, cool stuff.
• Koji also showed me around on how to use diaggui and awggui for taking measurements with any of the channels.

### Preliminary measurement for calibration scheme

We verified that we can send discrete frequency excitation signals to ETMX actuators directly and see a corresponding peak in the spectrum of beatnote frequency between fiber-coupled X-end IR laser and main laser IR pickoff.

• I sent excitation signal at 200 Hz, 250 Hz and 270 Hz at C1:SUS-ETMX_LSC_EXC channel using awggui with an amplitude of 100 cts and gain of 2.
• I measured corresponding peaks in the beatnote spectrum using diaggui.
• Page 1 shows the ASD data for the 4 measurements taken with Hanning window and averaging of 10.
• Page 2 shows close up Spectrum data for the 4 measurements taken with flattop window and averaging of 10.
• I converted this frequency signal into displacement by using conversion factor $\nu_{FSR}/\frac{\lambda}{2}$ or $\frac{L \lambda}{c}$.

If full interferometer had been locked, we could have used the DARM error signal output to calibrate it against this measurement.

Data

 Attachment 1: PreliminaryCalibrationData.pdf  178 kB  Uploaded Thu Oct 29 11:25:27 2020
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