Using a PDA05CF2 InGaAs PD in transmission of the filter cavity until it is needed (earmarked for RBQ things I believe).

The 1550 TRANS beam is larger than the small diode on this new PD. Avoiding a lens/ND filter combo for now as there isn't much space. With the beam large it is not saturated.

Took 5 measurements using the same method as described in previous posts except in order to rapidly cut off the incoming light we instead provide a sudden jump on the PDH error signal offset, just above the point where it can't possibly lock anymore. In this case the numbers were:

-Offset required for lock: 2.3 mV

-Error amplitude: 11 mVpp

-Set offset for kick: 8 mV

An example of the data 1550ringdowntransandrefl.png. This looks very similar to the Matt Evans paper measurements Lee linked earlier. Fitting an exponential to this ringdown 1550fitonthedopplerringdown.png yields a finesse of 3300. This is very close to the expected value with the quoted mirror specs. A few nit picks with this so far:

-The decaying exponential should pierce the middle of sine wave if its of the form sin(w*t) * e^-t/tau + C. It clearly doesn't, although is close. The residual (just data - fit) show this not symmetric about 0 residuals.png.

-This is only 1 point, I will process the additional points tomorrow to get an average. 

-The reflection decay is not as clean as the Matt Evans paper and I'm unsure why yet. Would like to get that data working as well. There is additional information to extract.