There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.
Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.
My plan on connecting the servo:
I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.
If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.
I also need to check which power splitters and mixers are suitable for our power output.
The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)
The box has two knobs that allow us to change gain and LO phase manually.
From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.
I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,
the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.