Jenne, Craig We are wondering about our IMC open loop gain, in particular, why do we have to put the servo board In1 gain slider to 31 dB to get a UGF of 100 kHz, when in the past it was much lower (I think around 8 dB for O2) to achieve the same UGF? We checked the power on the REFL PD with 1.6 watts incident and the mode cleaner unlocked. It was 4.2 mW, which was pretty close to what the calibrated ADC output reported of 3.9 mW. The IMC signal chain probably hasn't changed much since O2.
24.1 MHz modulation depth? Right now, with the new EOM, you have a modulation depth of 12.5 mrad (see 41889 ). It looks like there wasn't a measurement of the 24.1 MHz gamma just before swapping the EOM, but I found a measurement by Volker in 2012, entry 4957, that reports m = 0.13 for 24.1 MHz. So that would account for a 20 dB optical gain reduction.
The estimated current modulation at 24.1MHz is 11mrad. The modulation depth before the EOM replacement was estimated to be 14mrad.
- Kiwamu made the modulation depth measurement and got an upper limit of 40mrad [LHO ALOG 9395]
- Evan needed a fudge factor of 0.35 to match the IMC OLTF with the model. I.e. The estimated modulation depth was 14mrad. [LHO ALOG 22188]
- The newly installed EOM was tested at Caltech. It showed the modulation response of 2.1mradpk/Vpk [40m ELOG 13725]
- With the RF combiner amplifier D1800116 installed, the RF driver at the EOM was inferred to be 24.34 dBm (5.21Vpk = 3.68Vrms). [LHO ALOG 41889]
- Therefore the estimated current 24.1MHz modulation is 2.1e-3 * 5.21 = 11mrad