Night Vision Microchannel plate manufacturing

[nutation]

Microchannel plates are the key component in an image intensifier tube. The intensifier tube acts a little bit like two TV tubes connected back-to-back. The first layer is a photocathode, which emits electrons when struck by incoming light, like a TV tube in reverse. The electrons travel through the tiny (a few microns wide) tubes in the microchannel plate, bouncing off the insides of the tubes and freeing up more electrons. This is what amplifies the signal. The resulting cascade of electrons then strikes a phosphor screen, which emits light, like a TV tube. This is the image you see in your NODs.

Here is an interesting overview of the manufacturing process for microchannel plates from an undergraduate optics textbook, The Light Fantastic by Ian Kenyon.

The raw materials for the construction of a plate are uniform cylindrical glass rods with lead glass cladding over a borosilicate crown core. These rods are stacked together, and the stack is heated and stretched. The resultant long multiple rod is sliced into lengths which are again stacked together, heated and stretched. After enough repititions of this sequence the resulting solid block now contains millions of individual rods fused together, and this block is sliced to produce individual plates. Finally the softer borosilicate crown glass cores are etched away by a hydrogen atmosphere.

This partially explains why image intensifier tubes have such a variation in their specs - it's tricky to get uniform channels when you're stretching glass like taffy, and folding it over like you're forging a katana. Not to mention all the other steps needed to get the rest of the tube to work.

 

[Tchitcherine]

Interesting. The stretching method of forming those microchannel tubes is reminiscent of stretching heated theta tubing to form micropipette electrodes used for recording action potential in single neurons.