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acid etching. A technique that uniformly thins CCDs to approximately 10 µm so that an image can be focused on the back of the parallel register (where there is no gate structure). See back-illuminated CCD.

adapter. A device that allows a CCD camera to be attached to a variety of scientific instruments or lenses. Also referred to as mount adapter and lens mount adapter. See also C-mount and F-mount.

A/D converter. Analog-to-digital converter. In a CCD camera system, the electronic circuitry that converts the analog information (continuous amplitudes) acquired by the detector into the digital data (quantified, discrete steps) used for image display.

ADU. Analog-to-digital unit. A number representing a CCD's output. The relationship between the ADUs generated and the number of electrons acquired on the CCD is defined by the system gain. Intensities given in ADUs provide a convenient method for comparing images and data generated by different cameras. Also referred to as count and digital number.

AIMO. Advanced inverted-mode operation. A trade name used by e2v Technologies to represent MPP operation.

analog-to-digital converter. See A/D converter.

analog-to-digital unit. See ADU.

angstrom. A unit of measure equal to 0.1nanometers.

arc lamp. Often used as a light source on a microscope, an electric light in which a current traverses a gas between two incandescent electrodes and generates an arc that produces light. Arc lamps have a limited lifetime. Also called an arc light.

AR coating: Anti-reflective coating. Applied to either CCD surface or the vacuum window to minimize reflections and increase transmission.



back-illuminated CCD. A CCD that has been uniformly reduced to a thickness of approximately 10 µm so that an image can be focused on the back of the parallel register (where there is no gate structure). Thinned CCDs exhibit high sensitivity to photons ranging from the soft x-ray to the near-infrared regions of the spectrum. Since light is hitting the silicon directly instead of passing through the gate structure, sensitivity to blue light is particularly good. Many back-illuminated CCDs also have ultraviolet coatings that "down convert" UV light into the visible portion of the spectrum, further increasing QE. Also called backside-illuminated CCD and back-thinned CCD.

backside-illuminated CCD. See back-illuminated CCD.

back-thinned CCD. See back-illuminated CCD.

bias. In a CCD camera system, the minimum intensity required for each exposure (equivalent to performing a zero-second exposure with the shutter closed). Without adding any light, the bias allows charge to be read out on the CCD while raising the intensity level high enough to ensure that the camera does not deliver a negative number to the A/D converter. (The A/D converter only works in the set of positive numbers and has no instructions for processing negative numbers.) The bias, which is not user selectable, is set at the factory and remains stable over the lifetime of the camera system. See CCD readout.

binned readout. Within a CCD, the process of moving charge that has been binned to an output amplifier for conversion to an image. See binning.

binning. In CCD imaging technology, the technique of combining the charge from adjacent pixels so that the total charge can be read out as an image at the expense of spatial resolution.

binning factor. The number of pixels to be combined on a CCD during binning. A binning factor of 2x2 means that the adjacent pixels in two rows and two columns (a total of four pixels) are combined for CCD readout.

bit depth. The number of bits (smallest unit of information in a notation using the binary system) that are digitized by a system's A/D converter.

BNC connector. A connector used to couple coaxial cables to high-frequency electronic equipment, such as a video monitor.

brazing - A process by which two similar or dissimilar materials are joined together at very high temperatures. At PI/Acton, brazing is used to join stainless steel vacuum chamber to the vacuum window. This offers a superior seal compared to traditional epoxy based bonding which can outgas and degrade vacuum overtime.

bulb mode. A type of exposure in which a trigger signal from an external source controls both the start and end of the exposure.



CCD. Charge-coupled device. A light-sensitive silicon chip often used as a photodetector in digital camera systems. CCDs are manufactured in a wide variety of formats, architectures, and grades. See CCD readout.

CCD readout. CCDs are analog devices. In order to obtain a digital signal that is appropriate for doing quantitative analysis, it is necessary to convert the analog signal to a digital format. When light is gathered on a CCD and is ready to be read out, a series of serial shifts and parallel shifts occurs. First, the rows are shifted in the serial direction towards the serial register. Once in the serial register, the data is shifted in the parallel direction out of the serial register, into the output node, and then into the A/D converter where the analog data is converted into a digital signal.

charge. In CCD imaging technology, a measure of the number of electrons..

charge-coupled device (CCD). See CCD.

charge smearing. Residual charge left behind in potential wells when an image is shifted within a CCD. Occurs when the image is shifted while the light is falling on the sensor.

charge transfer. (1) The ability of a CCD to transfer the charge in each individual pixel to the next pixel without any loss in the charge during the transfer. Scientific-grade CCDs typically have a charge-transfer efficiency (CTE) of 99.9998%, where 100% is perfect. (2) The process by which the electrons in one potential well are moved to an adjacent well.

Clock Induced Charge (CIC) - Unwanted electrons generated in the pixels due to charge clocking on the CCDs and EMCCDs. It is specified as electrons per pixel per readout. CIC is exposure time independent, where as dark charge is proportional to the exposure time. For more information, refer to on-chip multiplication gain tech note. See also spurious charge.

C-mount. A standard screw-in lens mount common to many scientific instruments. (Thread of lens and lens mount: 1-inch diameter, 32 threads/inch. Back focal length: 17.52 mm.)

CMOS. Complementary Metal Oxide Semiconductor- Semiconductor technology widely used to manufacture electronics devices and also used to manufacture light-sensitive device similar to CCD.

convolution. See image convolution.

cooled CCD. A charge-coupled device that is operated below ambient temperature in order to reduce or eliminate dark current. CCD cooling is often achieved via Peltier (thermoelectric) coolers or cooled liquid gases (e.g., LN).

correlated, double-sampling readout. A sampling technique used to achieve higher precision in CCD readout. The sampling circuit is reset to a predetermined reference level and then the actual pixel voltage is sampled in order to find the difference between the two. Using the resulting correlation minimizes read noise, especially in ultra-low-noise cameras.

count. See ADU.

CsI:TL: Cesium Iodide with Thallium - The phosphor composition with Thallium doping used to convert X-rays in to visible light around 550 nm



dark current. (1) The charge accumulated within a well, in the absence of light. (2) The background current that flows in a charge-coupled device or image intensifier of a camera system. Cooling the photodetector's primary imaging surface (i.e., the CCD's photoconductor or the image intensifier's photocathode) can reduce or eliminate dark current. Also called thermally generated charge.

dark current noise. See dark noise.

dark noise. The statistical variation of the dark current, equal to the square root of the dark current. Dark current can be subtracted from an image, while dark noise remains. Also called dark current noise.

deep-depletion CCD. A CCD that has been designed to provide enhanced near-infrared and high-energy x-ray sensitivity. These devices utilize a bias voltage applied to a thick layer of high-resistivity silicon in order to produce a "deeper" depletion region (active photosensitive area) than that of conventional CCDs. This architecture allows longer-wavelength photons to interact within the layer as opposed to merely penetrate it.

DIF: double image feature. Two distinct frames are captured separated by short inter-frame interval on an interline-transfer CCD.

digital. A scheme for representing data via quantized, discrete steps. See analog.

digital number [DN]. See ADU.

digitize. To convert data (or images) into a digital format.

Direct Detection (of X-rays) . A method used to detect low energy x-rays directly in the silicon of the CCD device.

down converter. In digital imaging, a material that absorbs higher-energy light photons and re-emits them as lower-energy light photons, thereby functioning as a "down" converter. See Metachrome ® II and Unichrome.

dynamic range. The ratio of the maximum (brightest) to minimum (darkest) signal levels that can be detected by a camera. For instance, a true 16-bit digital camera is capable of providing a dynamic range of 65,535:1.



EMCCD - Electron Multiplication CCD

EUV-Extreme ultra violet – The energy range from around 5 eV to 100 eV.

e-/ADU: see system gain

Electron Multiplication CCD - CCDs capable of achieving sub-electron read noise through on-chip multiplication gain [link to on-chip gain tech note]. Photoelectrons generated in pixels are multiplied by impact ionization process before the readout. EMCCDs are ideal for high speed, low light level applications such single molecule fluorescence and photon counting applications.

etaloning. In a standard back-illuminated CCD, reflections between the parallel front and back surfaces of the device that lead to unwanted fringes of constructive and destructive interference. This resonant effect is especially apparent in near-infrared region (>700nm) of the spectrum.

exposure time. (1) The length of time that a CCD is accumulating charge. (2) In many software programs, the name for the setting that determines the length of time that a CCD is accumulating charge.

excess noise factor - The statistical nature of the multiplication gain in EMCCDs results in excess noise in the output signal. Typically it is between 1.2 to 1,4. For more information, refer to on-chip multiplication gain tech note.



faceplate. In a CCD camera system, the front surface of the camera head, which often incorporates a window. The faceplate is sometimes used to support a target or phosphor (or to mount the camera head).

fiberoptic-coupled CCD. A CCD with a coherent fiberoptic bundle bonded to the CCD's imaging surface. Also referred to as fiberoptically coupled CCD, fiberoptic-bonded CCD, and fiberoptically bonded CCD.

fiberoptic coupling. A method of using a coherent fiberoptic bundle to transfer an image source to the imaging surface of the CCD.

fiberoptics. (1) Thin, transparent fibers of glass or plastic that transmit light throughout their length via a series of internal reflections. The fibers are encased in material (referred to as "cladding") that possesses a lower index of refraction. (2) A bundle of these fibers.

fill factor. A term that relates to the light-gathering area of a CCD. For instance, a CCD with 90% fill factor has an imaging array in which 10% of each pixel's area is insensitive to light. Most of the CCDs (except interline CCDs) have 100% fill factor.

Filmless intensifiers: The latest Gen III intensifiers that do not have an intermediate ion barrier between photocathode and MCP. As a result, they offer the highest sensitivity.

F-mount. A standard lens mount common to many scientific instruments. (Back focal length: 46.5 mm.)

fps. Frames per second.

frame. One image moved from a CCD in a full parallel shift.

frame buffer. In a digital imaging system, the hardware in which the frame memory (RAM that stores full frames of the image signal) resides.

frame-transfer CCD. A type of CCD used for quantitative electronic imaging. Frame-transfer CCDs divide the parallel register into two areas (arrays): an image array (for image collection) and a storage array (for image storage). After the image array is exposed to light, the electronic image is shifted to the storage array and read out. A frame-transfer CCD can operate without a shutter, running continuously at high rates.

front-illuminated CCD. A CCD in which the gate structure is located in front of the potential wells. Also called frontside-illuminated CCD.

frontside-illuminated CCD. See front-illuminated CCD.

full-frame CCD. The simplest type of CCD. Full-frame CCDs use the entire active parallel register to expose photons and to integrate and transport charge. They utilize a shutter to control the exposure and block light during CCD readout, preventing charge smearing.

full well capacity. The number of electrons that can be held in one potential well. It is assumed that all pixels on a CCD have the same well size and that each well can hold the same number of electrons.



GaAs: A photocathode material used on Gen III intensifiers.

GaAsP: A photocathode material used on filmless Gen III intensifiers

gain. See system gain.

gated interline CCD. See interline-transfer CCD.

gate structure. In a traditional CCD, the polysilicon structure located on the parallel register. Polysilicon gates are transparent at long wavelengths, but become opaque at wavelengths shorter than 400 nm.

gating. In an ICCD camera system, the application of a voltage that switches the image intensifier on and off in very short intervals. Gating allows capture of transient events.

Gd2O2S: TB : Gadolinium Oxysulfide with Thallium – The polycrystalline phosphor composition with Thallium doping used to convert X-rays in to visible light at 550 nm.

Gen II intensifiers: Intensifiers characterized by bi-, multi-alkali (e.g., S20) type photocathode materials

Gen III intensifiers: Gen III intensifiers use GaAs or GaAsP intensifiers for high quantum efficiency. See also filmless intensifiers.

gray level. The brightness of a pixel in an image, expressed as an integer. Gray levels range from 0 (black) to 255 (white) for an 8-bit digital signal, and from 0 (black) to 4095 (white) for a 12-bit digital signal. Also referred to as gray value. See ADU.

gray value. See gray level.



HCCD camera. High-performance CCD camera. A CCD-based digital imaging system that utilizes advanced design features, such as low-noise electronics and cooled-detector technology, to optimize camera capabilities for scientific or industrial imaging applications.

high-speed framing. The process by which frames are read from a CCD at a rapid rate.

horizontal register. See serial register.

host computer. The primary or controlling computer for a digital camera.


ICCD camera. Intensified CCD camera. A digital imaging (or spectroscopy) system that utilizes an image intensifier coupled to a CCD. These cameras offer high sensitivity in ultra-low-light-level conditions. Gating can be utilized to provide better temporal resolution.

ICL. Image Control Language. A library of commands used to communicate with PVCAM ®, an exclusive (Roper Scientific) universal programming interface. Also referred to as an ICL library. Applies to most Photometrics brand cameras.

image array. The portion of a frame-transfer CCD that is exposed to light (and in which the image is collected). After the CCD is exposed, charge is shifted to the other half of the device, the storage array.

image averaging. A method of reducing random image noise by averaging a pixel's brightness throughout a series of successive frames.

Image Control Language. See ICL.

image convolution. In digital imaging, the replacement of each pixel's gray level with a new value that has been adjusted to take into account the values of neighboring pixels. The degree to which the image is either smoothed or sharpened depends upon the specific calculations performed. Also called convolution.

image intensifier. A vacuum-tube device, generally 18 to 25 mm in diameter, that comprises a photocathode input (a coating of multi-alkali or semiconductor layers on the inside of the input window) and a phosphor screen (a fluorescing phosphor coating on the inside of the output window). Also included are either simple grid-shaped electrodes (early intensifier technology) to accelerate electrons through the tube or a complex electron-multiplying microchannel plate (later intensifier technology).

impact ionization. See on-chip multiplication gain.

indium gallium arsenide. See InGaAs.

indium tin oxide. See ITO.

Indirect Detection (of X-rays) . A method used in which X-ray energy is converted in to visible photon energy using phosphor / Scintillator and then detected using CCD or CMOS device.

infrared [IR]. The region beyond the visible spectrum at the red end, typically greater than 770 nm.

InGaAs. Indium gallium arsenide. A material used in some detectors (e.g., PDAs) to provide higher QE in the near-infrared region of the spectrum (up to 2.2um).

integration. The act of accumulating signal or charge on a CCD. Also called exposure.

interline CCD. See interline-transfer CCD.

interline mask. Opaque strips that span an interline-transfer CCD and function as storage areas.

interline-transfer CCD. Also called interline CCD. A type of CCD in which the parallel register is subdivided so that, like a Venetian blind, opaque strips span and mask the columns of pixels. The masks act as storage areas. When the CCD is exposed to light, the image accumulates in the exposed areas (photosites) of the parallel register. In the serial register, the entire image is under the interline mask when it shifts for CCD readout. It is possible to shift the integrated charge quickly (200 ns) under the storage areas. Since these devices function as a fast shutter (or gate), they are also sometimes referred to as gated interline CCDs. See microlenses.

inverted operation. See MPP.

ion barrier: A film between Gen III intensifier’s photocathode and MCP. It protects photocathode from the back streaming ions traveling at high velocity.

ITO. Indium tin oxide. A material used in some CCD gates to provide higher QE, particularly in the blue-green region of the spectrum.



kinetics: A special readout mode in which only a portion of the detector is exposed and then shifted repeatedly on to the rest of the chip. Used to achieve fast temporal resolution.


light. A form of electromagnetic radiation. Visible light (400 nm to 770 nm) can be perceived by the unaided human eye. See infrared and ultraviolet.

linearity. In CCD imaging technology, precise linearity dictates that an object that is twice as bright as another object will appear exactly twice as bright in the resultant image.

liquid nitrogen cooling. See LN cooling.

LN cooling. Cooling of the CCD by direct contact of liquid nitrogen to the CCD cold block. The CCD is not run at LN temperature (-200°C) because the charge-transfer efficiency of CCD arrays actually begins to suffer at such a low temperature. Thus, operation is usually regulated between -120°C and -60°C in order to optimally decrease dark current without unduly compromising charge-transfer efficiency.



mask. See interline mask.

MCP. Microchannel plate. One of the major components of an image intensifier. A slightly conductive glass substrate with millions of parallel traversing channels containing a secondary electron emitter on their inner walls. Each channel acts analogously to a standard photomultiplier device.

Medium X-ray energy. The X-ray energy spectrum from around 5 keV to 17 keV.

megapixel. A term used to describe a CCD whose imaging array contains at least one million pixels.

Metachrome ® II. A proprietary (Roper Scientific) phosphor coating for CCDs that extends detector sensitivity to below 200 nm. Metachrome II is transparent from 400 nm to 1100 nm and does not degrade over time.

microchannel plate. See MCP.

microlenses. Small lenses that increase the fill factor of interline-transfer CCDs by redirecting incident light away from the masked columns (or storage arrays) to the pixels' photosensitive areas.

MPP. Multi-pinned-phase operation. A mode that reduces the rate of dark current generation by a factor of 20 or more, relaxing CCD cooling requirements to the level where a thermoelectric cooler is sufficient for most applications. Also called inverted operation.

multi-pinned-phase operation. See MPP.



near infrared [NIR]. The region of the spectrum from about 0.77 µm to about 3.0 µm.

noise. An unwanted or undesirable signal. See system noise.


on-chip accumulation: refers to adding of multiple exposures right on the interline CCD or ICCD before a single readout. This increases signal-to-noise ratio.

on-chip multiplication gain. A technology that enables multiplication of charge (i.e., electrons) collected in each pixel of the CCD’s active array. Secondary electrons are generated via an impact-ionization process that is initiated and sustained when higher-than-typical voltages are applied to an “extended” portion of the CCD’s serial register. Multiplying the signal above the read noise of the output amplifier enables ultra-low-light detection at high operation speeds. (Some CCD cameras with on-chip multiplication gain utilize two output amplifiers, an “on-chip multiplication gain” amplifier that allows the camera to be used for low-light, high-speed applications and a “traditional” amplifier for wide-dynamic-range applications.)

opaque mask. In CCD imaging technology, a light-impenetrable material that is used to shield selected parts of a photosensitive surface. Opaque masks are used in interline-transfer CCDs and frame-transfer CCDs.

open electrode: a type of front illuminated CCD architecture in which fewer number of gates are used to allow more photons to reach the depletion area.

origin. In a CCD, the point located closest to the output node.

outgassing: gradual release of gaseous molecules in a vacuum chamber that degrades long term vacuum performance. High performance vacuum designs avoid it by using vacuum grade materials and advanced vacuum processing techniques. See XP cooling technology.

output amplifier. A mechanism in the CCD that amplifies the electrons in the output node sufficiently to get the signal to the A/D converter. The output amplifier is the primary source of read noise. Also called a readout amplifier.

output node. The location on a CCD (often a single pixel adjacent to the serial register) where charge is collected as a discrete picture element for CCD readout. Data enters the output node from the serial register and exits to the A/D converter.



parallel binning. The accumulation of multiple rows of charge in a CCD's serial register. The amount of charge shifted is defined by the user-specified binning factor. Also called vertical binning. See CCD readout.

parallel binning factor. In the parallel register of a CCD, the number of pixels (in the parallel direction) to be shifted to the serial register, read out, and processed into an image. The binning factor is specified by the user in the imaging software prior to exposure of the CCD. See CCD readout.

parallel direction. In a serial, parallel (s, p) coordinate system, the direction that begins at the origin and runs perpendicular to the serial register. Also called vertical direction. See CCD readout.

parallel register. In a CCD, a large, square array that contains many potential wells (pixels). When the CCD is exposed to light, charge accumulates in the potential wells, which when shifted and read out, form an image. Also called a vertical register. See CCD readout.

parallel shift. In a CCD, columnar movement of charge from one or more pixels to an adjacent row. The movement continues until the number of pixels to be binned (specified by the user) are emptied into the serial register. See binning and CCD readout.

parallel size. In CCD imaging technology, the size of the ROI (in pixels) extending in the parallel direction.

PDA. Photodiode array. A linear array of discrete photodiodes on an integrated-circuit chip used in digital detection systems.

Peltier effect. The transfer of heat in the opposite direction of the current flow. By pumping current through a "Peltier stack" to a heat sink, heat can be removed from a CCD. The heat sink is cooled by circulating liquid or air. The temperature must be regulated.

phosphor. A chemical substance that fluoresces when excited by x-rays, an electron beam, or ultraviolet radiation. Phosphors are composed of rare earth oxides or halides (e.g., gadolinium, lanthanum, yttrium) and usually emit green light with decay times ranging from hundreds of nanoseconds to a few milliseconds.

phosphor screen. One of the major components of an image intensifier. Electrons exiting the microchannel plate (MCP) are accelerated by a constant voltage and strike the screen, where they are converted back into light photons for detection by a CCD.

photocathode. One of the major components of an image intensifier. Coatings on the photocathode convert a portion of the incident light photons into electrons. Good QE is critical, as photons that are not captured by the photocathode are lost from the final signal produced by the intensifier.

photodiode array. See PDA.

photometry. The measurement of the properties of light, particularly (luminous) intensity.

photon-noise-limited operation. In CCD imaging technology, operating the detection system at levels of noise so low that photon (shot) noise is the dominant noise source.

photon (shot) noise. Unwanted or undesirable disturbance that is a fundamental property of the quantum nature of light. Photon noise is always present in an imaging system.

pixel. Picture element. The smallest element in a visual display.

poisson distribution. A probability function used to model the density of counts of a randomly occurring event obtained during a specified interval of time.

potential well. In a CCD, a discrete region within the device

Definitions of terms used in imaging, spectroscopy and x-ray applications and products.