Alastair and I have been working on getting the AOM double-pass setup going. We have borrowed a curved Y1 from Peter to use as a retroreflector while we wait for the one we ordered. We are using a Tektronix FG through the 2-W MiniCircuits RF amp on the shelf to drive the AOM at the moment, and that appears to work decently well. We are running into issues with alignment, however.
Right now, we can get the 1st-order beam isolated with an iris and reflected back along the same path back into the AOM, but what comes back out isn't very clean. What we should see is the singly diffracted beam that gets reflected straight back through the AOM (without a second diffraction), and then the doubly diffracted beam--what we want--which should be a little dimmer and should lie exactly along the input beam. We tried lowering the AOM drive power until only one beam was left (the single-pass beam), but this never happened; all we got was something that looked like two dim beams close together or one very elliptical one.
We think it is because we don't have any way of adjusting the orientation of the AOM at the moment. Alastair has drawn up a new mount which will allow us to put a tilt stage on top. In the meantime, we will try to get something remotely reasonable out and attempt to lock the cavity with that.