I redesigned the cuvette holder finally, this is just the prototype but she works great. It looks a little ruff I know, but this is just in the "proof of concept" mode. The cuvette holder is made from a high density, non-compressible black foam material.

The cuvette fits nicely in a collum cut at 12mm square @ 37mm in length down the holder's middle, so 3 sides are completely enveloped so light has no were else to go but back inside the cuvette and back out twoard the detector's slit.

The view in the picture above is were the excitation light source enters, the outside diameter is 22mm and has a conical cut at the end @ 12mm ( very tricky to make these cuts using an Exacto knife set!)

The resean I made the conical cut and outside diameter was to accommodate my high power LEDs, which their lenses have an outside diameter of 22mm, so all I have to do when I want to use them, is push them in and the angle is always the same.

TOP VIEW

SIDE VIEW

DETAILED VIEW

LIGHT SOURCE ENTRANCE VIEW

TOP VIEW FOR CUVETTE HOLDER

FRONT VIEW

BOTTOM VIEW

DETECTOR ENTRANCE VIEW