Night Vision

Prince Verma
6th Sem E&IE

A few years ago, it was very easy for intruders and militants from neighboring countries to cross the border and sneak into India with almost no interception. They used to carry out subversive activities and return back to their country of origin, leaving behind a trail of mass destruction in bordering states.
It had always been a big problem to have a good vision in sensitive areas at a distance in starlight night. Despite of this there’re other problems like recording weak images directly on film or in astronomy & spectrometry. To have a good vision of less illuminant objects, all we need is to amplify the images, which is provided by intensifier tube.
Image intensifier tube is a device for electronically amplifying images, consisting of a photocathode (light sensitive electron emitter) and a phosphor screen. The photocathode converts the incoming photons to photo electrons by collision ionization.
3rd generation intensifier
Continuous research in intensifier technology led to the development of micro channel plate with variable gain micro channel plate made it possible to increase the luminance gain of a single intensifier stage to at least 10000 which is continuously variable, unlike earlier intensifiers. A micro channel plate is an array of tiny channel electron multipliers that can be used to amplify an electron beam containing spatial information. The inside surface of the cylindrical micro channel is processed to have semi conducting surface.
Each cylindrical channel combines the function of the dynode structure in a conventional photo multiplier with the function of the resistor chain that divides voltage potential among that separate dynodes made up of cesium antimonide, magnesium oxide and beryllium oxide. Each channel is a tiny glass tube whose length is about 40 times more than its on diameter. The inner surface is made semiconducting through a reduction process. So it emits secondary electrons when bombarded with primary electrons that have been accelerated in an electric field. Electrons enters the multiplier & strike the wall to produce secondary electrons, which are accelerated axially along the channel by an electric field applied between the electrodes. Transmission energy of emission causes the electrons to traverse the channel so that they again collide with the channel wall & produce still more secondary electrons. Repetition of this process inside the channel enables production of a large no of electrons coming out from exit point of the micro channel.
The overall gain of a channel depends upon the applied voltage across the inlet & outlet ports, length to diameter ratio of the channel, & the type of semiconducting surface of the inside wall controlling the secondary emission characteristics.
Reduced size , weight and improved performance of micro channel tubes compared to conventional cascade tubes, have opened up new application areas for image intensifiers. These include military night-viewing binoculars, head-mounted binoculars, hand held starlight telescopes and many applications in astronomy and spectrometry.