Intensified charge-coupled device
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An intensified charge-coupled device (ICCD) is a CCD that is optically connected to an image intensifier, that is mounted in front of the CCD.
An image intensifier includes three functional elements: a photocathode, a micro-channel plate (MCP) and a phosphor screen. These three elements are mounted one close behind the other in the mentioned sequence. The photons which are coming from the light source fall onto the photocathode, thereby generating photoelectrons. The photoelectrons are accelerated towards the MCP by an electrical control voltage, applied between photocathode and MCP. The electrons are multiplied inside of the MCP and thereafter accelerated towards the phosphor screen. The phosphor screen finally converts the multiplied electrons back to photons which are guided to the CCD by a fiber optic or a lens.
An image intensifier inherently includes a shutter functionality: If the control voltage between the photocathode and the MCP is reversed, the emitted photoelectrons are not accelerated towards the MCP but return to the photocathode. Thus, no electrons are multiplied and emitted by the MCP, no electrons are going to the phosphor screen and no light is emitted from the image intensifier. In this case no light falls onto the CCD which means that the shutter is closed. The process of reversing the control voltage at the photocathode is called gating and therefor ICCD's are also called gateable CCD cameras.
Beside of the extremely high sensitivity of ICCD cameras, which enable single photon detection, the gateability is one of the major advantages of the ICCD over the EMCCD cameras. The highest performing ICCD cameras enable shutter times as short as 200 picoseconds.
Example: The light travels 300.000 km per second, which is 7.5 times around the earth. In 200 picoseconds the light travels only 6 cm.
ICCD cameras are in general somewhat higher in price than EMCCD cameras because they need the expensive image intensifier. On the other hand EMCCD cameras need a cooling system to cool the EMCCD chip down to temperatures around 170 K. This cooling system adds additional costs to the EMCCD camera and often yields heavy condensation problems in the application.
ICCDs are used in night vision devices and in a large variety of scientific applications.
[edit] See also
- STANFORD COMPUTER OPTICS - ICCD Technology Review A comprehensive information site concerning Image Intensified CCD camera technology
[edit] Commercial links
- STANFORD COMPUTER OPTICS - Manufacturer of scientific ultra high speed ICCD camera systems
