With the 775 OFC3 cavity lock successful, it is time to work on 1550. This requires mode matching the cavity. The light is diverging when it exits the cavity, with a waist of 581 um, roughly .6 m before the exit of the cavity (on M1 of OFC2). I adjusted the inter cavity mirrors position to maximize the amount of the length the light can travel as this is better for mode matching in this case. The two intercavity mirrors are at 15 and 18 inches from the cavity exit. The OFC3 cavity input mirror is at 29 inches. We want a waist here of 577.7 um (according to my finesse calculations of the cavity). JAMMT spits out an f=2m and f=1m lens solution based on the lens we have available. I've assembled these lens, moved the mirrors back into their positions, roughly placed them for now. See attached image for the calculation.

I am going to attempt to align into the next cavity using OFC2 1550 light. This poses a challenge because you need to make the two wavelengths coresonant and then lock on 775. Because the bandwidth of the 1550 cavity is so low and the lock quality is poor (and there seems to be 1550 -> 775 drift via the aom) it makes the test light being used very unstable. Will attempt this after lunch.