We're cool. For a couple days now. The CTC100 was set to maintain the thermal shields of both cavities at 120K.
With the current drivers in limbo I couldn't check what worried me most: That the mirrors may have plopped off due to insufficient heat transfer. I brought both drivers back to working order, one remains not installed for testing, but I installed the other one and fired up the lasers one after the other to look for back-reflections.
Upon turning the light on I saw reflected light immediately. A bit misaligned but surprinsingly close to the incident beam. The following procedure proved quite successful for both paths, it took less than 10 minutes each to recover the (frontal) alignment:
It's a major relief to know that the mirrors stayed on and that the bonding strategy worked as intended.
Next, the transmission path will need to be realigned. Last week we received the 4" extruded M2ISS PD mounts, the PCBs, and the circuit parts. Anchal and I will begin assembly and if all goes well we will have shot noise limited TransPD readout soon.
Design of the AC-coupled ISS servo also moves forward and we'll probably be ready to order the parts next week.