I'm optimizing the AOM to make sure that we have max power, and to minimize pointing  due to frequency change, and minimize ellipticity of the transmitted beam.  With the current status, the ellipticity of the beam is 0.59. I'll check what happen to the visibility of ACAV with this beam shape.

  Today I decided to optimize the AOM since I removed it for inspection (I thought it was broken, but it's not). Before I put the AOM back to its place, I made sure that the double-passed beam path overlaps with itself nicely, and parallel to the table plane. Then I inserted the AOM in the beam path, and adjusted the position(tilt/yaw) until the first order beam's power was maximized and got the beam with ellipticity = 0.59. 

   With the non gaussian beam profile we will have less power in ACAV, more noise on RFPD. In addition,  the visibility of the cavity will be reduce and we have to measure it so that we can estimate the power input to the cavity accurately. This number will effect the calculation of our photothermal noise.