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MIF (ITF Control)

yutaro.enomoto - 20:45 Monday 17 December 2018 (7415)

X arm transmission of the main laser

There is discrepancy between expected transmission and measured transmission.

= Measured =
10000cnts by PDA100A2 with the gain set to 60dB, which corresponds to 10.4 uW.
There are two beam splitters for IR from ETMX to the PD, this number corresponds to the transmission of 42 uW.

= Expected =
IMC transmission is ~ 500mW. There are PRM and BS, whose transmissivity are 0.1 and 0.5, respectively, so the power injected to X arm is 25 mW.
Using the measured finesse of ~1400, carrier power ratio of 0.88, and the transmission of I/ETMX characterized by Hirose-san (4437 ppm and 6.8 ppm),
the transmission is expected to be 120 uW.

There is a factor of ~3 discrepancy. Why???

Comments to this report:

yutaro.enomoto - 11:49 Tuesday 18 December 2018 (7419)

I had to take the effect of the optical filter attached on the PDA100A2 into account, which has ~70 % transmission for 1064 nm.
Then, measured transmission is 60 uW.
Still there is a facto of ~ 2 discrepancy. Is there a beam splitter I don't count in?