In order to find a good crystal temperature setpoint, working both for the master laser and the squeezing laser, we investigated temperatures from the current value, which is 23.7C, up to 31.4C.
The mode hops appears as an additional error signal while scanning the SL piezo.
| ML crystal temp | gps UTC | considerations | |
| 26.8 C | 10:06:00 | ||
| 26.4 C | 10:08:00 | ||
| 26.0 C | 10:09:00 | ||
| 25.7 C | 10:11:00 | we observed a peak appearing close to the error signal which, however is not a mode hop | |
| 25.8 C | 10:12:30 | ||
| 25.5 C | 10:16:00 | the error signal starts to worsen | |
| 25.3 C | 10:20:00 | a second error signal appeared (mode hop, probably the same mentioned in https://logbook.virgo-gw.eu/virgo/?r=67348) | fig. 1 |
| 24.8 C | 10:23:00 | the mode hop and the fundamental mode error signals have the same amplitude | fig.2 |
| 24.6 C | 10:24:00 | the mode hop disappear | |
| 23.7 C | 10:28:00 | this is the nominal temperature. However some peaks equally spaced are visible (noise at the 14MHz harmonics?) (fig.3 and 6) | |
| 27.3 C | 10:33: 00 | it seems a good setpoint | fig.4 |
| 27.9 C | 10:35:00 | faint error signal | |
| 28.1 C | 10:37:00 | mode hop | fig. 5 |
| 29.0 C | 10:39:00 | another good setpoint | |
| 31.4 C | 10:44:00 | mode hop |
In conclusion, a temperature around 29.7 C seems the best candidate since there are no spurious peaks and it is in the middle betwwen two mode hops. Also 27.3 C has a good shape but it is closer to the 28.1 C mode hop.
