Participaint: Chienming, Shurong and Yuhang

Our measurement method: Injecting bright alignment beam(BAB) and pump beam inside OPO. Scanning phase with 500Hz but scanning OPO's PZT with only 5Hz. Then we use small amplitude of OPO's PZT to see the parametric gain effect inside the scanning peak. As you can see from the first picture.

Then by using this oscillated peak, we did the alignment of the pump beam into OPO. The improvement of alignment will bring more amplification for the peak of scanning. So we aligned the two steering mirrors between GRMC and OPO. After alignment, we get that peak as figure 2.

Then we tried to do this for pump power from 10mW to 79mW. For looking at parametric gain more clearly, we stop the scanning of OPO. On contrast, we manually tune OPO around resonance and use cursor to mark down the maximum and minimum of the oscillation. The result of these values is shown in tha attached figure 3.

Then we fit this result with the formula

gain = (1+B/Bth)^2/(1-B^2/Bth^2)^2   where B is the pumping field amplitude:  P = B^2

We found a threshold of 80mW. We also clearly see the lasing when we provide 79mW of green pump.