hi!, i think they already exist!
There is a dutch article on internet....i'll try to translate it into english.....
Operation of a photomultiplier tube:
A photomultiplier tube or PMT is a detector which uses the photo-electric effect to convert light into an electrical current.
The main parts of a PMT are the photo-cathode, the dynodes and the anode. They have been brought into a vacuum glass tube
The Dynode-stage:multiplying electrons
A photon goes into the tube trough the glass. it loosens an electron from the photo-cathode
The electron is led into the dynode-stage by a 'focus-electrode'
Because of the electro-magnetic field the electron is accelerated before it strikes the first dynode. Here the impact will loosen more electrons.
These electrons in turn will by attracted by the next dynode and be accelerated..
At every dynode more electrons will be loosened until all electrons are caught at the anode
Because of the number of electrons now available are enought to measure a current....out of the 1 foton it began with...
Well it's quit a long article, i'll summarize the rest.
The dynodes are on high + voltage, the photo-kathode is held at a very negative voltage.. to get the electrons to go to the next dynode every following dynode will be on a higher voltage then the one preceding it...(else they would stick to one dynode)
These voltages are created using a voltage divider
Because the density of the electrons getting closer on the way to the anode, the em-field there will be disrupted by the space-charge, by using bigger values of resistance at the anode the em-field will be restored which will benefit respons and linearity...
Greetz,
Henk