Jim W, Cheryl, Corey, Nutsinee, Kiwamu,
Over the weekend Jim, Cheryl, Corey and Nutsinee kindly tested various CO2 configuration for me. The data so far indicate that
- Raising CO2X seems to improve some jitter peaks (152, 364, 620 and 1080 Hz) and broadband above 3 kHz.
- Raising CO2Y seems to degrade the sensitivity.
I would like to see some more data points with the CO2X laser higher than 0.4 W while maintaining CO2Y at 0 W.
Some details
The attached are the DARM spectra from various different times. Also, below shows a list of the CO2 settings that people tried during this weekend.
| time | Laser power that CO2X has been [W] | Laser power that CO2Y has been [W] | Goodnees | |
| ref 0 | 11:20 29/Oct/2016 | 0.2 | 0 | OK |
| ref 1 | 12:20 29/Oct/2016 | 0.2 | 0.4 | bad |
| ref 2 | 15:00 29/Oct/2016 | 0.4 | 0 | good |
| ref 3 | 18:00 29/Oct/2016 | 0.4 | 0 | good |
| ref 4 | 6:30 30/Oct/2016 | 0.4 | 0.2 | OK |
| ref 5 | 18:00 30/Oct/2016 | 0.4 | 0 | good |
| ref 6 | 10:00 31/Oct/2016 | 0.3 | 0.1 | bad-ish |
| ref 7 | 11:30 31/Oct/2016 | 0.4 | 0.2 | bad-ish |
| ref 8 | 13:00 31/Oct/2016 | 0.5 | 0.3 | bad-ish |
| ref 9 | 14:00 31/Oct/2016 | 0.6 | 0.4 | bad-ish |
As one can see, having a high CO2X seems to improve the noise curve. We should try putting even more power on CO2X (meaning more than 0.4 W) next time.
Interestingly, the peak at 3340 Hz (SRM resonance, 27488) becomes taller when the TCS tunings become worse. This is consistent with a theory that high frequency part of the SRCL coupling is due to HOMs in the SRC. We might be able to use this peak to evaluate the good ness of the CO2 tunings.
