Baffle Structures
Out of the 3×1017 photons emitted in the laser pulse, some fraction (a few percent) will remain in the laser enclosure as scattered light. If even one hundred of these reach the APD, this could spell trouble for detecting the internal corner-cube pulse. Even though the APD is off when the laser fires, photo-electrons generated in the APD could still be bumping around in the device at turn-on some 30 to 40 ns after the laser pulse. Keeping the light paths from laser beam to detector to a minimum is imperative.
A series of sheet-metal assemblies will mount on the optical table around the various optical paths. This should be done in such a way that removal is easy for access to optics. They should be able to slip into place without making mechanical contact with optics. We may want to use some of that coarse black hair-like liner to seal against the optical mounts without rigidly contacting them.
The details of this task depend in large part on the final mechanical arrangement of optics on the bench, as wel as other mounting structures. It is best saved until much of this other work has been done.