shoshana.apple@LIGO.ORG - posted 15:58, Thursday 13 August 2026 (91512)
Mode Hopping in CRS laser
- Watching the CRS laser since it's been installed, we've noticed some mode hopping occurring where there are these dramatic jumps between wavelengths (picture 1) or small just happening very frequently (picture 2)
- This morning we added some thermal paste and some scrap metal on the CRS laser to try and help with the thermal regulation.
- I looked back at the time series from when the NRS laser was plugged in and while there is still some mode hopping occurring, it doesn't have the same big hops, rather smaller ones which occur much less frequently (picture 3).
- While power cycling the TEC, we found that the mode hopping in the CRS laser reduces if the TEC is set to 10.896kΩ-10.899kΩ (rather than the recommended 10.72kΩ). If the value is between 10.72kΩ and 10.896kΩ or above 10.899kΩ, the mode hopping worsens. In this range the mode hopping looks more like the NRS laser mode hopping (picture 4) with the occasional big jumps, but much less frequently than with other TEC settings.
- Using 10.896kΩ the laser temperature is set to 24.42o C, rather than 24.5oC when the TEC is set to 10.72kΩ
- We'll keep an eye on the performance and the amount of noise hopping as
- While it's good to have reduced the amount of mode hopping, it doesn't seem to improve the actual CRS performance, which is as expected given the NRS laser didn't improve the performance. At this point it seems like the excess noise isn't from the laser itself or the thermal regulation of the laser and is from something else.
Images attached to this report
