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Image intensifier tube structure and components

Cross-section of an image intensifier tube. From left: X-rays strike the large caesium iodide input phosphor (x-rays to light); the photocathode converts light to electrons; electrostatic focusing electrodes accelerate and focus the electrons across the evacuated tube onto a much smaller output phosphor, producing a bright, minified electron image at the anode. Brightness gain equals minification gain (input/output area ratio) times flux gain (acceleration).

Image intensifier tube: structure and gain Cross-section of an image intensifier tube. From left: X-rays strike the large caesium iodide input phosphor (x-rays to light); the photocathode converts light to electrons; electrostatic focusing electrodes accelerate and focus the electrons across the evacuated tube onto a much smaller output phosphor, producing a bright, minified electron image at the anode. Brightness gain equals minification gain (input/output area ratio) times flux gain (acceleration). Image intensifier tube: structure and gain X-rays Photocathode: light → electrons Electrostatic focusing electrodes: accelerate + focus (~25–35 kV) Evacuated tube (high vacuum) Input phosphor (CsI): x-rays → light Output phosphor — bright, minified image Anode (aluminium) Brightness gain Minification gain = (D_in / D_out)² — image concentrated onto the smaller output screen Flux gain — electrons accelerated (~25–35 kV), so each releases many more light photons Brightness gain = minification gain × flux gain (typically several thousand)
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