To investigate more about the optical losses in our set-up and have idea how to reduce more about optical losses, the measurement about half-wave plate (HWP) losses was done.

The test used the infrared beam before IRMC, which is directly from main laser. By measuring infrared beam power with power meter before and after HWP, the optical losses was evaluated. The power meter was fixed in this measurement while the HWP was taken away or put back several times. Therefore, for each HWP, there were several measured data. The difference between each measurement is that beam is hitting on HWP with different angle and different position.

Three HWP were tested: Two used CVI HWP (being used for SQZ reflected from FC, being used before injection to filter cavity), a new CVI HWP, a new thorlab HWP.

The result of optical losses measurement is listed in the following table: