Yuhang and Michael
We locked the SHG in the new setup and took some temporary power level references. The locking is not perfect - the SHG temperature was optimised (reading 3.140 on TED200C) to maximise the amount of transmitted green power, and by leaving a cursor level we could see that the lock was offset a bit from the maximum level of the transmission peak. This requires some adjusting of the custom servo filter (i.e. ask Pierre Prat...). Anyway, that's why this is only temporary.
Figure 1 shows the new SHG setup. We measured the following power levels:
Incident IR (measured before dichroic): 684.3 mW
Reflected green (measured before FI): 237 mW
Reflected IR (measured before ND2 on photodetector): ~ 87 mW.
Compared to previous measurements, it is almost exactly the same. A 1:1 efficiency calculation p_green/p_IR gives 0.347.
Yuhang and Marc
We found that the SHG is misaligned this morning. This misalignment cannot be corrected by only tilting the steering mirrors before SHG. This is a bit strange for us. The situation of the misalignment is shown in the attached figure.
It was found later that this is caused by: the small scan amplitude of the locking servo.
The scan amplitude is adjusted to be small so that the lock loop can be engaged around the TEM00 resonant peak. However, today, due to the drift of cavity length, the small scan range is located accidentally around the first order resonance peak. This created the confusion at the beginning.