A xenon flash lamp is an electric glow discharge lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations. Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble In Physics, coherence is a property of waves that enables stationary (i
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Construction
The lamp comprises a sealed tube, often made of fused quartz, which is filled with a mixture of gases, primarily xenon, and electrodes to carry electrical current to the gas mixture. Xenon (ˈzɛnɒn or) is a Chemical element represented by the symbol Xe. Additionally, a high voltage power source is necessary to energize the gas mixture; this high voltage is usually stored on a capacitor so as to allow very speedy delivery of very high electrical current when the lamp is triggered. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.
The glass envelope is most commonly a thin tube, which may be straight, or bent into a number of different shapes, including helical, "U" shape, and circular (to surround a camera lens for shadowless photography—'ring flashes'). A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing The electrodes protrude into each end of the tube, and are connected to a capacitor that is charged to a relatively high voltage. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors This is usually between 250 and 2000 volts, depending on the length of the tube, and the specific gas mixture. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force.
Operation
A flash is initiated by first ionizing the gas mixture, then sending a very large pulse of current through the ionized gas. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Pulsed power is the term used to describe the science and technology of accumulating Energy over a relatively long period of time and releasing it very quickly thus increasing Ionization is necessary to decrease the electrical resistance of the gas so that a pulse measuring as much as thousands of amperes can travel through the tube. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second The initial ionization pulse may be generated by a tesla coil. A Tesla coil is a type of resonant transformer circuit invented by Serbian-American scientist Nikola Tesla around 1891 A short high voltage peak produces the first ions at the sharp tip of the cathode (the housing is grounded). Field emission (FE is the emission of electrons from the surface of a condensed phase into another phase due to the presence of high electric fields A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device By applying radio frequency voltage the ions do not need to reach the anode, but couple capacitively to the housing (and the anode). Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz This may be enhanced by putting a metal band onto the glass or a wire that is wrapped around the glass tube or by using water cooling, since water has a high dielectric constant and if ionized also conducts. Measurement The relative static permittivity εr can be measured for static Electric fields as follows first the Capacitance of a test When this current pulse travels through the tube, it excites electrons surrounding the xenon atoms causing them to jump to higher energy levels. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The atoms' electrons immediately drop back to a lower orbit, producing photons in the process. Depending on the size and application of the flashlamp, xenon fill pressures may range from a few kilopascals to tens of kilopascals (0. 01–0. 1 atmosphere or tens to hundreds of torr). The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. For low electrode wear the electrode needs to be at high temperature for the thermionic emission of electrons. Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy
Output spectrum
As with all ionized gases, xenon flash lamps emit light in various spectral lines. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared This is the same phenomenon that gives neon signs their characteristic color. Neon signs are luminous-tube signs that contain neon or other inert gases at a low pressure However, for xenon, there are enough spectral lines, and they are distributed across the spectrum in such a way, that to the human eye the light appears mostly white. White is a Color, the perception which is evoked by Light that stimulates all three types of color sensitive Cone cells in the Human eye The spectral profile of a xenon arc peaks in the green range, which is well matched to many applications involving visible light. This is the primary motivation for selecting xenon as a filler in spite of its high cost; krypton is also occasionally used, although it is even more expensive. Krypton (ˈkrɪptən or /ˈkrɪptɒn/ from kryptos "hidden" is a Chemical element with the symbol Kr and Atomic number 36 Krypton has much greater output in the near-IR range, which is better matched to the absorption profile of Nd:YAG laser media than xenon emissions.
During normal operation in most photographic-type systems, the spectral component of a flashlamp's emission is overshadowed by blackbody radiation. The proportion of light produced by spectral action compared to thermal action depends on current density in the arc. Higher current densities favor blackbody radiation over spectral radiation. For this reason, many laser systems intentionally utilize lower current densities than photographic flashes since more narrow spectral lines are usually favorable for pumping lasers, while a broadband output is better for photographic purposes. Production of greenish blue light instead of pure white is a clear indication of low-current density operation.
Intensity and duration of flash
For short pulses the number of emitted electrons from the cathode is the limit. For longer pulses or continuous operation the cooling is the limit. Discharge durations for common flashlamps are in the microsecond to a few milliseconds range and can have repetition rates of hundreds of hertz. To help compare Orders of magnitude of different Times this page lists times between 10&minus6 seconds and 10&minus5 seconds (1 micro A millisecond (from Milli- and Second; abbreviation ms is one thousandth of a Second. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second.
The flash that emanates from a xenon flash lamp may be so intense that it can ignite flammable materials within a short distance of the tube. Carbon nanotubes are particularly susceptible to this spontaneous ignition when exposed to the light from a flashtube. [1] Similar effects may be exploited for use in aesthetic or medical procedures known as Intense Pulsed Light (IPL) treatments. IPL can be used for treatments such as hair removal and destroying lesions or moles. A lesion is any abnormal tissue found on or in an organism usually damaged by disease or trauma A mole, technically known as a melanocytic Nevus, is a small dark spot on human Skin.
Applications
Because the duration of the flash that is emitted by a xenon flash tube can be accurately controlled, and due to the high intensity of the light, xenon flash lamps are commonly used as photographic strobe lights. Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing Xenon flashlamps are also used in the technique of very high speed or "stop-motion" photography, which was pioneered by Harold Edgerton in the 1930s. For the police officer see Harry Edgerton Harold Eugene "Doc" Edgerton ( April 6, 1903 &ndash January Because they can generate bright, attention-getting flashes with a relatively small continuous input of electrical power, they are also used in warning lights, emergency vehicle lighting, fire alarm annunciator devices (horn lights), aircraft anticollision beacons, and other similar applications. Emergency vehicle lighting refers to any of several visual warning devices which may be known as light bars or beacons fitted to a vehicle and used when the driver wishes to convey to An automatic fire alarm system is designed to detect the unwanted presence of fire by monitoring environmental changes associated with combustion A Navigation light is a coloured source of illumination on an Aircraft, spacecraft or waterborne vessel, used to signal a craft's position Heading
Due to their high-intensity and relative brightness at short wavelengths (extending into the ultraviolet) and short pulsewidths, flashlamps are also ideally suited as light sources for pumping atoms in a laser to excited states where they can subsequently be stimulated to emit coherent monochromatic light. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Laser pumping is the act of energy transfer from an external source into the Gain medium of a Laser. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. Proper selection of the filler gas is crucial here, so the maximum of radiated output energy is concentrated in the bands that are the best absorbed by the lasing medium; e. The active laser medium or gain medium is the source of optical Gain within a Laser. g. krypton flashlamps are more suitable than xenon flashlamps for pumping Nd:YAG lasers, as krypton emission in near infrared is better matching to the absorption spectrum of Nd:YAG. NdYAG ( neodymium-doped yttrium aluminium garnet; NdY3Al5O12) is a Crystal that is used as a lasing medium
Xenon flash lamps have been used to produce an intense flash of white light, some of which is absorbed by Nd:glass that produces the laser power for inertial confinement fusion. Neodymium (ˌniːoʊˈdɪmiəm is a Chemical element with the symbol Nd and Atomic number 60 Inertial confinement fusion ( ICF) is a process where Nuclear fusion reactions are initiated by heating and compressing a fuel target typically in the form of In total about 1 to 1. 5% of the electrical power fed into the flash tubes is turned into useful laser light for this application.
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References
See also
A flash is a device used in Photography that produces an instantaneous flash of artificial Light This is a list of sources of Light, including both natural and artificial sources and both processes and devices.Dictionary
xenon flash lamp
-noun
- A lamp that produces a very short, but very intense, flash of white light; used in photography and in photocoagulation
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