Alexa, Stefan, Sheila and Kiwamu
Yesterday, we set up an optical spectrum analyzer on the PSL table to measure the characteristic of the EOM. The results look good except for the 24 MHz resonance . The resonance for the 24 MHz sideband is apart from the modulation frequency by 250 kHz or so. However the IMC doesn't need a large modulation depth and the IMC locking has been OK, we are good. Also, I took some impedance data and will put those data together into a DCC document for a record purpose.
The plots below are the measured modulation depth when driven hard as a function of the modulation frequencies. The vertical dashed-lines represent our actual modulation frequencies i.e. f1 = 9099471 Hz , f_mc = 24078360 Hz and f5 = 5 x f1.
A document summarizing the measurements and their results is now available in DCC (https://dcc.ligo.org/LIGO-E1300966).
I kept forgetting to report the important information regarding to the modulation depths. Here are the estimated modulation depths:
| Modulation depths [rad] | Peak height measured with OSA | RF power at the input | |
| 9 MHz | 0.1 | 20 mV | 12.3 dBm |
| 24 MHz | less than 0.04 | less than 3 mV | 13.8 dBm |
| 45 MHz | 0.07 | 10 mV | 10.8 dBm |
The peak height of the carrier light was about 7.3 V. I used 2 * sqrt(V_sideband / V_carrier) to derive the modulation depths.