microchannel array

A microchannel array (or microchannel plate detector) is a type of electromagnetic radiation (EMR) or particle sensor that detects particles (which can be photons) over a planar area, such as might record a focused image within a camera or dispersed EMR within a spectrograph. It is useful for energetic photons of ultraviolet or X-rays. It requires a vacuum to operate (for free flow of the electrons, like those in a vacuum tube) and has been used as a technology in space telescope instruments where the vacuum is no challenge. It senses particles entering an array of microchannels, very narrow passages through a plate (microchannel plate) made of a substance that acts as a photocathode, i.e., a material designed to undergo photoionization (or an analogous reaction triggered by whatever kind of particle is being sensed) when particles enter and hit the sides of the channels, and that then produces secondary emission from the resulting electrons, i.e., more electrons. At the far end of the channel, these secondary electrons are detected, e.g., by charging a pixel of a CCD from which data can be extracted. The channels are often curved, so as to assure that the sensor (CCD) generally receives electrons from the secondary effect rather than the incoming particles, which makes its sensitivity more uniform. All the plate's microchannels are generally identically curved, such as with a particular arc shape. The term MAMA for multi-anode microchannel array is a particular type of microchannel array.