R&D (FilterCavity)
NaokiAritomi - 22:20, Tuesday 15 June 2021 (2578)
IR injection mode matching with new beam spot

I measured the IR injection mode matching with new beam spot which has more stable IR transmission.

First I optimized IR injection alignment with new beam spot. I checked the IR injection alignment by changing AOM frequency. The mode matching is 95.6%. Note that AA and BS pointing were engaged during this measurement. 

After the IR injection alignment, IR transmission was 460 with 430uW injection. According to our experience, the IR transmission should be 490 with 430uW injection. The possible reason of the smaller IR transmission is that the IR transmission is off centered in transmission PD with new beam spot.

AOM frequency (MHz) mode IR transmission
109.53805 TEM00 460
109.93494 pitch 100
110.33183 LG 105
  offset 94
 
After the IR injection alignment, IR transmission was 460 with 430uW injection. 
According to our experience, the IR transmission should be 490 with 430uW injection. I'm not sure why it is smaller now.