What I did

• Replaced two pedestals used in the chamber
• Removed the output fused silica mirror and re-aligned the beam. At this moment, the cavity direction was not good as the beam reflected by the apex mirror could not reach the center of the output mirror. So I tweaked the cavity direction.
• Re-installed the output fused silica mirror and checked the transmitted laser power.

Some results

The transmitted laser power was about 1.03 uW with 6.4 mW input power.
Assuming no loss in the apex mirror , the transmittance of the fused silica mirror is estimated about 0.016%.
In practice, there are some loss in the apex mirror and the transmittance of the fused silica mirror is slightly larger than 0.016%.
According to the spec sheet, the transmittance of the fused silica mirror is 0.017%.
So this result is reasonable and the loss in the fused silica mirror is not too large, about 30ppm with the assumption that the reflectivity of the fused silica is same as shown in the spec sheet (99.98%)
In any case, I need to compose the cavity and see the flash.

Next step

• Tweak the alignment of the output mirror to pick off the reflected beam. In fact, I could see the reflected beam on PD by adjusting the direction of the output mirror. Shim sheet, however, is indispensable to maintain the optimal direction.