elenna.capote@LIGO.ORG - posted 14:04, Tuesday 18 March 2025 - last comment - 10:05, Friday 16 May 2025(83437)
Single Bounce OMC scans taken - process notes
I took two single bounce OMC scans today with the help of TJ and Tony. Here are some notes to future me and others to reference if we want to do single bounce scans:
- align one ITM. We chose ITMY today because of work happening with the oplev that required ITMY to be aligned
- for this scan, I increased the input power to 10 W
- first check if the fast shutter is OPEN (silly mistake, spent a few minutes wondering where the beam was)
- take the OMC guardian to DOWN. After the fast shutter mistake, TJ and I were fighting to scan and realized that the guardian was set to "OFF_RESONANCE" and overriding us as we scanned
- I turned on the AS centering loops by hand, DC3 and DC4 P/Y (this aligns OM1 and 2 onto the AS WFS)
- To ensure alignment to AS_C was good, TJ and I ran SR2_ALIGN in the ALIGN_IFO guardian (after this I had to reengage the DC centering loops because the ALIGN_IFO guardian turned them off going to DOWN)
- I saw an off-centered beam on the OMC QPDs, so I engaged the OMC ASC master gain which centered the QPDs
- There was a moment where I thought the PZT2 offset mattered, so I changed it. I see now that it probably didn't matter, and only effects where the scan starts
- I used an OMC scan template in [userapps] omc/h1/templates/OMC_scan_single_bounce.xml
- run some scans! Today, I ran a scan with nominal settings, and another scan with the RF9 modulation down by 3 dBm and the RF45 modulation down by 6 dBm, which are the settings in full lock
- my scans are saved in [userapps] omc/h1/templates/OMC_scan_single_bounce_RF_cal.xml
Edit to add: unfortunately the scan results from today look pretty bad. In short, the peaks look "lopsided" somehow, and so I'm not sure the results are usable. Looking back at Jennie W's previous scans, it looks like she had to slow them down to 200 second scans. I only did a 100 second scan with amplitude 105 so maybe I scanned too fast. I'm not sure what the correct resolution of this is, because the scans I did in 2022 were 100 second scans and the results were fine. Adding this note here for reference in the future to think about the appropriate scan length and amplitude.
Jennie, Sheila, and I ran OMC scans this morning and realized that the proper way to slow down the scan to avoid weird saturation effects is to reduce the excitation frequency in the template. The nominal templates have excitation frequencies of 0.01 Hz, so sweeping over 200 seconds just sweeps at the same speed twice. To sweep once, slower, you have to increase the sweep time to 200 seconds AND reduce the sweep frequency to 0.005 Hz.
Sheila and I want to note some things that are "obvious" but easily forgotten: