Let's get some overhead photos of the table with lots of the parts and beampaths labeled please. It will help in understanding these results so far.
For example, based on the peak height in the spectrum analyzer and the transmission diode's transimpedance gain, what is the contrast ratio for the two beams?
And let's get that signal demodulated with a Rubidium Marconi and fed into the DAQ! We should be able to get some long term data with it.
The peak on the spectrum analyser is at -68dBV. Converting this to volts (10^(-68/20)) we get 0.00040V
The transimpedance gain for the New Focus 1811 is 40V/mA and the response is approximately 0.75A/W. This means we have about 10^-9 amps of photocurrent, and 0.013uW of laser power.
The laser power on the photodiode is 16uW, so we have a contrast of about 0.08%......which doesn't seem like a lot. Admittedly our beams are different sizes coming out of the cavity and they are going through just one lens to focus down onto the PD, so perhaps this is where most of the contrast is lost. The beams are approximately the same power. We can increase the power on the PD a little as well.