A continuation on the previous measurements where we seen a drop in green power at 34 Celcius in both SHG 1 and 2 in a cavity setup.

To exclude the effect of optical cavity, we took off the front mirror of the cavity and took the double pass measurements under slightly different beam alignment. Then the single pass measurement is done by removing the rear mirror. The single pass measurement result fits the model, but not the double pass (not sure why).

Rebuild SHG 2, and measure the phase matching condition with lower pump at 10mW (in comparison all previous measurement were done with 60mW), and the same drop in power is seen in 34 Celcius.

Conclusion: the sinc curve phase matching measurement is only reliable when done in single pass setup. The measurement done in cavity setup is not definitive in diagnosing crystal condition.