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MIF (General)

yutaro.enomoto - 0:28 Friday 08 April 2016 (1423)

Optical gain of RF/DC lock of MICH

[Miyo, Enomoto]
Today we measured optical gain (count/m) of RF/DC lock of iKAGRA Michelson interferometer.

Summary
-- contrast: (6280-1450) / (6280+1450) = 62 %
-- optical gain (RF): 9000/2*4*pi/lambda = (5.3 +/- 0.2) *10^10 counts/m
-- optical gain (DC): (6280-1450)/2*4*pi/lambda = 2.9 *10^10 counts/m

How we did
First, we maximized the contrast of REFL by aligning ETMX/Y.
Then we measured peak-to-peak amplitude of REFL DC PD output (LSC-REFL_PDA1_DC_OUT) and demodulated signal of REFL RF PD (LSC-REFL_PDA1_RF17_Q_MON) by watching these channels using StripTools with BS, ETMX, and ETMY freely swinging (in length degree of freedom).

Results
-- max and min of DC output: max 6280, min 1450. --> contrast 62 %
-- p-p amplitude of error signal (RF demodulated): 9000 +/- 300
Note that the contrast was almost constant during the measurement. This error (+/- 300, I mean) includes effect of the fluctuation of the contrast, but not the degrade of the contrast which has a time scale of hours to days.

Comments to this report:

yutaro.enomoto - 15:42 Friday 08 April 2016 (1435)

Nakano-san inserted 20 dB attenuator between RF voltage source for LO and the demodulator for MICH. So optical gain of the RF lock has been probably changed.

We have to re-measure it!!

keiko.kokeyama9 - 21:15 Saturday 09 April 2016 (1455)

I remeasured the optical gain set.

Summary
-- contrast: (7068-1577) / (7068+1577) = 64 %
-- optical gain (RF I): 2800/2*4*pi/lambda = 1.7 *10^10 counts/m
-- optical gain (RF Q): 9000/2*4*pi/lambda = 5.3*10^10 counts/m
-- optical gain (DC): (7068-1577)/2*4*pi/lambda = 3.2 *10^10 counts/m

How we did
Same as Enomoto-kun's original post.

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