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Photocathode
A photocathode is a surface engineered to convert light (photons) into electrons using the photoelectric effect. Photocathodes are important in accelerator physics where they are utilised in a photoinjector to generate high brightness electron beams. Electron beams generated with photocathodes are commonly used for free electron lasers and for ultrafast electron diffraction. Photocathodes are also commonly used as the negatively charged electrode in a light detection device such as a photomultiplier, phototube and image intensifier. Important Properties Quantum Efficiency (QE) Quantum efficiency is a unitless number that measures the sensitivity of the photocathode to light. It is the ratio of the number of electrons emitted to the number of incident photons. Rao, T., & Dowell, D. H. (2013). ''An engineering guide to photoinjectors''. CreateSpace Independent Publishing. This property depends on the wavelength of light being used to illuminate the photocathode. For man ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Image Intensifier
An image intensifier or image intensifier tube is a vacuum tube device for increasing the intensity of available light in an optical system to allow use under low-light conditions, such as at night, to facilitate visual imaging of low-light processes, such as fluorescence of materials in X-rays or gamma rays ( X-ray image intensifier), or for conversion of non-visible light sources, such as near-infrared or short wave infrared to visible. They operate by converting photons of light into electrons, amplifying the electrons (usually with a microchannel plate), and then converting the amplified electrons back into photons for viewing. They are used in devices such as night-vision goggles. Introduction Image intensifier tubes (IITs) are optoelectronic devices that allow many devices, such as night vision devices and medical imaging devices, to function. They convert low levels of light from various wavelengths into visible quantities of light at a single wavelength. Operation Im ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Night Vision Device
A night-vision device (NVD), also known as a night optical/observation device (NOD) or night-vision goggle (NVG), is an optoelectronic device that allows visualization of images in low levels of light, improving the user's night vision. The device enhances ambient visible light and converts near-infrared light into visible light which can then be seen by humans; this is known as I2 ( image intensification). By comparison, viewing of infrared thermal radiation is referred to as thermal imaging and operates in a different section of the infrared spectrum. A night vision device usually consists of an image intensifier tube, a protective housing, and an optional mounting system. Many NVDs also include a protective sacrificial lens, mounted over the front/ objective lens to prevent damage by environmental hazards, while some incorporate telescopic lens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Video Camera Tube
Video camera tubes are devices based on the cathode-ray tube that were used in television cameras to capture television images, prior to the introduction of charge-coupled device (CCD) image sensors in the 1980s. Several different types of tubes were in use from the early 1930s, and as late as the 1990s. In these tubes, an cathode ray, electron beam is scanned across an image of the scene to be broadcast focused on a target. This generated a current that is dependent on the brightness of the image on the target at the scan point. The size of the striking ray is tiny compared to the size of the target, allowing 480–486 horizontal scan lines per image in the NTSC format, 576 lines in PAL, and as many as 1035 lines in Multiple sub-Nyquist sampling encoding, Hi-Vision. Cathode-ray tube Any vacuum tube which operates using a focused beam of electrons, originally called cathode rays, is known as a cathode-ray tube (CRT). These are usually seen as display devices as used in older (i. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mean Transverse Energy
In accelerator physics, the mean transverse energy (MTE) is a quantity that describes the variance of the transverse momentum of a beam. While the quantity has a defined value for any particle beam, it is generally used in the context of photoinjectors for electron beams. Definition For a beam consisting of N particles with momenta \mathbf and mass m traveling prominently in the \hat direction the mean transverse energy is given by : \text = \frac \sum_ \frac Where \mathbf is the component of the momentum \mathbf perpendicular to the beam axis \hat. For a continuous, normalized distribution of particles f(\mathbf, \mathbf) the MTE is : \text = \int \frac f(\mathbf, \mathbf) \,dp_ \,d^p_ Relation to Other Quantities Emittance is a common quantity in beam physics which describes the volume of a beam in phase space The phase space of a physical system is the set of all possible physical states of the system when described by a given parameterization. Each possible stat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoelectric Effect
The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, solid state, and quantum chemistry to draw inferences about the properties of atoms, molecules and solids. The effect has found use in electronic devices specialized for light detection and precisely timed electron emission. The experimental results disagree with classical electromagnetism, which predicts that continuous light waves transfer energy to electrons, which would then be emitted when they accumulate enough energy. An alteration in the intensity of light would theoretically change the kinetic energy of the emitted electrons, with sufficiently dim light resulting in a delayed emission. The experimental results instead show that electrons are dislodged only when the light exceeds a certain frequency—regardless of the ligh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoinjector
A photoinjector is a type of source for intense electron beams which relies on the photoelectric effect. A laser pulse incident onto the cathode of a photoinjector drives electrons out of it, and into the accelerating field of the electron gun. In comparison with the widespread thermionic electron gun, photoinjectors produce electron beams of higher brightness, which means more particles packed into smaller volume of phase space ( beam emittance). Photoinjectors serve as the main electron source for single-pass synchrotron light sources, such as free-electron lasers and for ultrafast electron diffraction setups. The first RF photoinjector was developed in 1985 at Los Alamos National Laboratory and used as the source for a free-electron-laser experiment. High-brightness electron beams produced by photoinjectors are used directly or indirectly to probe the molecular, atomic and nuclear structure of matter for fundamental research, as well as material characterization. A photoinjecto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultrafast Electron Diffraction
Ultrafast electron diffraction, also known as femtosecond electron diffraction, is a pump-probe experimental method based on the combination of optical pump-probe spectroscopy and electron diffraction. Ultrafast electron diffraction provides information on the dynamical changes of the structure of materials. It is very similar to time resolved crystallography, but instead of using X-rays as the probe, it uses electrons. In the ultrafast electron diffraction technique, a femtosecond (10–15 second) laser optical pulse excites (pumps) a sample into an excited, usually non-equilibrium, state. The pump pulse may induce chemical, electronic or structural transitions. After a finite time interval, a femtosecond electron pulse is incident upon the sample. The electron pulse undergoes diffraction as a result of interacting with the sample. The diffraction signal is, subsequently, detected by an electron counting instrument such as a charge-coupled device camera. Specifically, aft ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Image Dissector
An image dissector, also called a dissector tube, is a video camera tube in which photocathode emissions create an "electron image" which is then swept up, down and across an anode to produce an electrical signal representing the visual image. It employs magnetic fields to keep the electron image in focus, and later models used electron multiplier to pick up the electrons.Horowitz, Paul and Winfield Hill, ''The Art of Electronics'', Second Edition Cambridge University Press, 1989, pp. 1000-1001. . The term had also been used for other kinds of early video camera tubes. Dissectors were used only briefly for research in television systems before being replaced by different much more sensitive tubes based on the charge-storage phenomenon like the [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triveni Rao
Triveni Rao is an Indian and American physicist and an expert on physics instrumentation. She is a senior physicist at the Brookhaven National Laboratory, acting head of the Instrumentation Facilities Division at the laboratory, and an adjunct professor in the Department of Physics and Astronomy at Stony Brook University. Education and career Originally from India, Rao completed a Ph.D. in physics at the University of Illinois Chicago in 1983, after also earning a master's degree there. After working in industry for a year, she joined the Brookhaven National Laboratory in 1985. Formerly the head of the Laser Applications Group at Brookhaven, she subsequently became associate division head of the Instrumentation Division, and then acting head of the Instrumentation Facilities Division. In 2023 she was funded by the Indian government by a Visiting Advance Joint Research Faculty Fellowship, for a visiting position at the Inter-University Accelerator Centre in Delhi. Research Rao' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phototube
A phototube or photoelectric cell is a type of gas filled tube, gas-filled or vacuum tube that is sensitive to light. Such a tube is more correctly called a 'photoemissive cell' to distinguish it from photovoltaic or photoconductive cells. Phototubes were previously more widely used but are now replaced in many applications by solid state photodetectors. The photomultiplier tube is one of the most sensitive light detectors, and is still widely used in physics research. Operating principles Phototubes operate according to the photoelectric effect: Incoming photons strike a photocathode, knocking electrons out of its surface, which are attracted to an anode. Thus current is dependent on the frequency and intensity of incoming photons. Unlike photomultiplier tubes, no amplification takes place, so the current through the device is typically of the order of a few microamperes. The light wavelength range over which the device is sensitive depends on the material used for the photo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vacuum Tube
A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It takes the form of an evacuated tubular envelope of glass or sometimes metal containing electrodes connected to external connection pins. The type known as a thermionic tube or thermionic valve utilizes thermionic emission of electrons from a hot cathode for fundamental Electronics, electronic functions such as signal amplifier, amplification and current Rectifier, rectification. Non-thermionic types such as vacuum phototubes achieve electron emission through the photoelectric effect, and are used for such purposes as the detection of light and measurement of its intensity. In both types the electrons are accelerated from the cathode to the anode by the electric field in the tube. The first, and simplest, vacuum tube, the diode or Flem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Free-electron Laser
A free-electron laser (FEL) is a fourth generation light source producing extremely brilliant and short pulses of radiation. An FEL functions much as a laser but employs relativistic electrons as a active laser medium, gain medium instead of using Laser, stimulated emission from atomic or molecular excitations. In an FEL, a ''bunch'' of electrons passes through a magnetic structure called an undulator or Wiggler (synchrotron), wiggler to generate radiation, which re-interacts with the electrons to make them emit coherently, exponentially increasing its intensity. As electron kinetic energy and undulator parameters can be adapted as desired, free-electron lasers are tunable laser, tunable and can be built for a wider frequency range than any other type of laser, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, ultraviolet, and X-ray. The first free-electron laser was developed by John Madey in 1971 at Stanford Uni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
