Daniel (on phone), Peter, Jason, Keita, Sheila, Kiwamu,

Today we set the diode current of the X end laser to the factory setting of 1.95 A. It had been for some reason set to 1.8 A.

This was motivated by the power fluctuation issue that Jenne reported the other day (36550). As a result, the green laser power became more stable, although it doesn't look like it has fixed the recent ALS issue of being difficult going through the ALS states.

(Symptom)

The end X laser intermittently ran into a situation where the power fluctuated by a few 10 % for unknown reason as reported in 36550. Today we ran into the same situation and therefore we decided to investigate this issue. As we studied the behavior, it turned out that the green laser power had a dependency on the laser temperature. This may be an indication that the laser was close to some bad mode hop condition or some sort. The behavior was clearly repeatable as we went to back to the same frequency (or crystal temperature).

(Fix)

Earlier Peter noticed that the laser current had been set to a lower value. However, since we weren't sure whether it had been purposely set or not, we initially decided to change the crystal temperature to escape from the mode hop region. However, in the end this didn't really work out because when we shifted all three lasers (PSL and both end lasers) by +800 MHz, the end X laser went into a good region where the laser power didn't change as a function of the laser frequency while the end Y laser went into a bad region.

Consulting with Keita, Sheila and Daniel. We decided to try out the diode current setting as another knob to escape from the bad region. This actually worked pretty well. All three lasers are now set to back to their nominal frequencies.