From yesterday, we found there are strange shape near the peak on the cavity scan, like there is some high frequency oscillation, so when we try to lock the cavity, the green beam also flash very speedily. We did some test, change the temperature of the cavity to not produce green, and we did no see these things then. So we guess that this is caused by the green maybe reflected back and sent into the laser.
But if everything works well, the Faraday Isolator should stop the reflect beams. So we checked the polarization again, try to get pure p or s polarization at the place we want. After that, the situation gets better, the peak looks normal, and the green stopped flashing. But the error signal sometimes still have some high frequency oscillation.(To further check tomorrow)
Before the two steering mirror, one of them is dichoric mirror and the other is normal mirror, for get rid of the green reflection, we changed the normal mirror with a second dichoric mirror.
Then we check the power everywhere, we have about 490mW at the output of the laser, 350 after the EOM and 230mW enter the cavity. So now nearly half of the power reach the cavity. With not very good alignment, we got 95mW in green finally, so now the green efficiency is 35%-40%. We try to measure the power reflect back after one of the dichoric mirror, 5% of green power is reflected.