An
intensified charge-coupled device (ICCD) is a
CCDA charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
that is optically connected to an image intensifier, that is mounted in front of the CCD.
An image intensifier includes three functional elements: a
photocathodeA photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound...
, a micro-channel plate (MCP) and a
phosphorA phosphor is a substance that exhibits the phenomenon of phosphorescence ....
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.
An
intensified charge-coupled device (ICCD) is a
CCDA charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
that is optically connected to an image intensifier, that is mounted in front of the CCD.
An image intensifier includes three functional elements: a
photocathodeA photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound...
, a micro-channel plate (MCP) and a
phosphorA phosphor is a substance that exhibits the phenomenon of phosphorescence ....
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
shutterIn photography, a shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene...
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-Neurobiology:*Gating , the opening or closing of ion channels*Sensory gating, a automatic process by which the brain adjusts to stimuli*Synaptic gating, neural circuits suppressing inputs through synapses...
and therefore ICCDs 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
picosecondA picosecond is 10-12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. The name is formed by the SI prefix pico and the SI unit second. It is abbreviated as ps....
s.
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
KThe kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero kelvin...
. 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.