Participaint: Chienming, Shurong and Yuhang

As we reported, we found the green production has an fluctuation. Following that, we found the similar fluctuation in the power of bright alignment beam and even the beam going to IR mode cleaner. Here we present the result of power monitoring at two different points and in three different situation. The position of monitoring is shown in the attached figure 1. We kept monitoring each case for around 4min.

Montioring point :

Situation 1: Block the beam going to SHG, almost no light going back.

          power fluctuation level is 0.29%

Situation 2: Lock SHG, both infrared and green going back.

          power fluctuation level is 3.9%

Situation 3: Tune SHG off-resonance, only infrared going back.

          power fluctuation level is 4.8%

Monitoring point 2:

situation 1: Lock SHG, both infrared and green going back.

          power fluctuation level is 1.6%

situation 2: Block the beam going to SHG, almost no light going back.

          power fluctuation level is 0.055%

Scanning cavity:

          In the last attached figure, we put the power of point 1 while scanning cavity. As you can see, Cavity resonance causes the drop of main laser power. However, there is one thing strange, when cavity is not resonance, the mainly laser power should be the same since the reflection of SHG is the same. But in the attached figure, we can see the feature caused not only by cavity resonance.  There is also a signal in-phase with the ramp signal. Maybe this is caused by the phase change of light. Need more investigation.

Conclusion: As we can see from the result, the monitoring point is only related to main laser. So we are sure the fluctuation comes from main laser. And we found the fluctuation will disappear only when there is no reflection. We also found the fluctuation will be even larger if there is more infrared reflection. And since even when there is no green relfection, fluctuation exists. We guess green should not be the main reason of this fluctuation.