Aso, Nakano
We measured the DC calibration factors of the AS RF PDs with the ITMX single bounce configuration.
We used the Thorlabs's thermal power meter (S310C).
AS PDA1: 4.4mW -> 1940cnts => 2.3e-3 mW/cnts
AS PDA2: 2.0mW -> 1360cnts => 1.5e-3 mW/cnts
[Aso, Nakano, Michimura]
We measured the optical throughput from BS output to the DARM photodiode (AS_PDA1).
Using independently measured PRM, ITMX and BS reflectivity/transmission, the measured value was about 4.6 %.
We have unknown 60% optical loss.
Details:
- Measured the power at AS PDA1 and PDA2 with ITMX single bounce (see attached).
- From K1:LAS-POW_IMC_DC_OUTPUT, the IMC output power during the measurement was 3.7 W, which gives 0.38 W at BS, assuming PRM transmission is 10.35% (JGW-L1605744) and there's no other large loss. This also gives 95 mW at BS output in ITMX single bounce.
- The measured power at AS PDA1 and PDA2 was 4.4 mW and 2.0 mW, respectively, as reported in klog #11756.
- This means that the optical throughput from BS output to AS PDA1 is 4.4 mW/95 mW = 4.6%.
- Since we have T=30% SRM, we don't currently have OSTM installed, and we have two beamsplitters in the AS table before PDA1, the expected optical throughput is 0.3*0.5*0.5 = 7.5%.
- This means that we have unknown 4.6/7.5 = 60% loss, which sounds kind of OK since there's OFI, viewports etc.
Next:
- Update the shot noise of the noise budget
