X-ray free electronic laser schema of operation A free electron laser, or FEL, is a laser that shares the same optical properties as conventional lasers such as emitting a beam consisting of coherent electromagnetic radiation which can reach high power, but which uses some very different operating principles to form the beam. Unlike gas, liquid, or solid-state lasers such as diode lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term free electron. This gives them the widest frequency range of any laser type, and makes many of them widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, to ultraviolet, to soft X-rays. by de:Horst Frank File links The following pages link to this file: Free electron laser Categories: GFDL images ...
by de:Horst Frank File links The following pages link to this file: Free electron laser Categories: GFDL images ...
For other uses, see Laser (disambiguation). ...
For the book by Sir Isaac Newton, see Opticks. ...
Beam may refer to: Look up beam in Wiktionary, the free dictionary. ...
Coherence is the property of wave-like states that enables them to exhibit interference. ...
This box: Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ...
For other uses, see Radiation (disambiguation). ...
The gas laser is a kind of laser in which some sort of gas (such as helium or neon) is discharged to produce the laser light. ...
For other uses, see Liquid (disambiguation). ...
A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as dye lasers or a gas such as gas lasers. ...
A laser diode is a laser where the active medium is a semiconductor p-n junction similar to that found in a light-emitting diode. ...
Relativistic electron beams (REBs) are streams of electrons moving at relativistic speeds. ...
Within a laser, the active laser medium or gain medium is the material that exhibits optical gain. ...
For other uses, see Frequency (disambiguation). ...
For other uses, see Wavelength (disambiguation). ...
This article is about the type of Electromagnetic radiation. ...
Electromagnetic waves sent at terahertz frequencies, known as terahertz radiation, terahertz waves, terahertz light, T-rays, T-light, T-lux and THz, are in the region of the electromagnetic spectrum between 300 gigahertz (3x1011 Hz) and 3 terahertz (3x1012 Hz), corresponding to the wavelength range starting at submillimeter (<1 millimeter...
For other uses, see Infrared (disambiguation). ...
Visible light redirects here. ...
For other uses, see Ultraviolet (disambiguation). ...
In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...
Beam creation To create a FEL, a beam of electrons is accelerated to relativistic speeds. The beam passes through a periodic, transverse magnetic field. This field is produced by arranging magnets with alternating poles along the beam path. This array of magnets is sometimes called an undulator, or a "wiggler", because it forces the electrons in the beam to assume a sinusoidal path. The acceleration of the electrons along this path results in the release of a photon (bremsstrahlung or synchrotron radiation, but not in the most common sense of either term). Magnetic field lines shown by iron filings Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box: In physics, the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. ...
For other uses, see Magnet (disambiguation). ...
An undulator is a device from high-energy physics and usually part of a larger installation, a synchrotron. ...
In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...
(help· info), (from the German bremsen, to brake and Strahlung, radiation, thus, braking radiation), is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. ...
General Electric synchrotron accelerator built in 1946, the origin of the discovery of synchrotron radiation. ...
Viewed relativistically in the rest frame of the electron, the magnetic field can be treated as if it were a virtual photon. The collision of an electron with the virtual photon creates a freely propagating photon (Compton scattering). Mirrors capture the released photons to generate resonant gain. Adjusting either the beam energy (speed/energy of the electrons) or the field strength tunes the wavelength easily and rapidly over a wide range. Because Compton scattering is complicated in and of itself, it is easier to say that the undulator forces the electrons onto a sinusoidal trajectory along the length axis (longitudinal direction) of the undulator in the undulator's rest frame, then transform to a new rest frame in which the undulator moves along the longitudinal direction such that the electrons oscillate about a fixed point at rest. The radiation is then simple dipole radiation due to the oscillations of the electrons about that fixed point. In the rest frame of the undulator, this dipole radiation will be seen as radiation with a shorter wavelength, propagating in a forward direction along the length of the undulator. In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ...
In physics, Compton scattering or the Compton effect, is the decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, when it interacts with matter. ...
A mirror, reflecting a vase. ...
An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. ...
For other uses, see Wavelength (disambiguation). ...
Since the energy of an emitted photon (radiation) depends upon the electron velocity and and magnetic field strength, the FEL can be tuned, i.e. the frequency or color can be controlled. For other uses, see Frequency (disambiguation). ...
Color is an important part of the visual arts. ...
What makes it a laser (light amplification by stimulated emission of radiation) is that the electron motion is in phase (coherent) with the field of the light already emitted, so that the fields add coherently. Since the intensity of light depends on the square of the field, this increases the light output. (Surprisingly, quantum mechanics is not required in this explanation.). In the rest frame moving along the undulator any radiation will still move with the speed of light and pass over the electrons and lets them communicate to get in synchronization. Often same light (that is radiation) is introduced from the outside. Depending on the position along the undulator the oscillation of an electrons is in phase or not in phase with this radiation. The light either tries to accelerate or decelerate these electrons. The electrons thereby gain or lose kinetic energy, and so move either faster or slower along the undulator. This causes the electrons to form bunches. Now they are synchronized, and will in turn emit synchronized (that is coherent) radiation. For other uses, see Laser (disambiguation). ...
In optics, stimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon. ...
Coherence is the property of wave-like states that enables them to exhibit interference. ...
For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ...
Accelerators Today, a free electron laser requires the use of an electron accelerator with its associated shielding, as accelerated electrons are a radiation hazard. These accelerators are typically powered by klystrons, which require a high voltage supply. Usually, the electron beam must be maintained in a vacuum which requires the use of numerous pumps along the beam path. Free electron lasers can achieve very high peak powers. Their tunability makes them highly desirable in several disciplines, including medical diagnosis and non-destructive testing. For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ...
Reflex klystron Type 2K25 or 723 A/B. The threaded adjustment rod on the right side allows the position of the reflector to be adjusted (by compressing the reflex cavity), and thus the natural resonant frequency of the device. ...
Look up Vacuum in Wiktionary, the free dictionary. ...
The Roots blower is one example of a vacuum pump A vacuum pump is a pump that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. ...
For the chemical substances known as medicines, see medication. ...
In general, diagnosis (plural diagnoses) has two distinct dictionary definitions. ...
From klystron to free electron laser
Basics In a klystron, an electron beam is accelerated by a 200 kV DC electric field. An electromagnetic wave interacts with it, modulating its velocity. In a drift tube this velocity distribution is converted to a density modulation. In a second interaction region, energy can be converted from the electron beam to the EM-wave or vice versa, depending on the relative phase with which both are fed. If energy is converted to the EM-wave, this device is called a klystron, otherwise it is a linear electron accelerator (linac). A charged particle beam is a group of electrically charged particles that have approximately the same kinetic energy and move in approximately the same direction. ...
The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). ...
Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...
In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ...
Electromagnetic radiation is a propagating wave in space with electric and magnetic components. ...
In telecommunications, modulation is the process of varying a periodic waveform, i. ...
Linear accelerator (LINAC) used for medical radiation therapy; example made by Siemens AG. A linear particle accelerator (also called a LINAC) is an electrical device for the acceleration of subatomic particles. ...
Interaction devices In a klystron or linac, the wavelength of the EM-wavelength is larger than the electron beam and various waveguide structures can be used to slow the EM-field to the speed of the electron density (group) velocity and at the same time provide E-fields in the direction of the electron motion. Look up waveguide in Wiktionary, the free dictionary. ...
In a gyrotron or free electron laser, the EM-wavelength is smaller than the electron beam and the electrons must be manipulated. Magnetic fields force them on a sinusoidal path, so as the EM-wave overtakes them, and the E-vector changes sign, the electrons change direction. Gyrotrons are high powered electron tubes which emit a millimeter wave beam by bunching electrons with cyclotron motion in a strong magnetic field. ...
Most interaction devices are tunable, but only a family of waveguides called traveling wave tubes allows one octave wide instant bandwidth and thus short pulses, but have cooling problems as they consist of helical wires or wire chambers. A traveling wave tube (TWT) is an electronic device used to produce high-power radio frequency signals. ...
For other uses, see Octave (disambiguation). ...
Quantum noise The amplified wave can be fed back, producing an oscillator. Free electron lasers in the visible region and above use so much energy that operation is only possible for short times. Lasers have quantum noise (optical shot noise) when they start. While this noise is damped over time, these energy hungry units cannot operate long enough to benefit from this damping, producing very unstable output. Shot noise consists of random fluctuations of the electric current in an electrical conductor, which are caused by the fact that the current is carried by discrete charges (electrons). ...
Photon noise simulation. ...
X-ray FELs The lack of suitable mirrors in the extreme ultraviolet and x-ray regimes prevent the operation of an FEL oscillator; consequently, there must be suitable amplification over a single pass of the electron beam through the undulator to make the FEL worthwhile. When the field extracts enough energy from the electrons over a single pass such that the field amplitude cannot be regarded as constant during the FEL process, the FEL is said to operate in the high-gain regime. In this case one can couple the single particle equations of motion to Maxwell's equations by describing the beam phase space via the Klimontovich distribution and using this distribution to source the paraxial wave equation for the slowly-varying electric field amplitude. Thereby the paraxial wave equation, together with the continuity equation, completely determine the dynamics of the field and beam during the FEL process.
Self-amplified spontaneous emission It is a fascinating fact that even if the initial field amplitude is zero, the FEL can still generate a laser through the process of Self-Amplified Spontaneous Emission (SASE); whereby, the (classical) shot noise, i.e. density perturbations in the electron beam, causes a noisy signal to be initially radiated. This noise becomes a seed for the FEL, allowing the FEL interaction to begin bunching the beam, which then radiates coherently till the energy spread in the beam, created by the FEL interaction, dominates, causing the FEL to saturate at some high power. The Linac Coherent Light Source (LCLS), currently being built at the Stanford Linear Accelerator, will operate as a SASE FEL, radiating at wavelengths down to 150 picometers. Free electron LASer in Hamburg (FLASH) has already demonstrated SASE principle to soft X-ray.
Seeded FELs One problem with SASE FELs is the lack of temporal coherence due to the noisy startup process. To avoid this one can "seed" an FEL with a laser, produced by more conventional means, tuned to the resonance of the FEL. This results in coherent amplification of the input signal such that the output laser quality is characterized by the seed. Although, this method becomes a problem at x-ray wavelengths because of the lack of conventional x-ray lasers. This problem can also be overcome by employing the method of High Gain Harmonic Generation (HGHG), whereby one first uses an undulator to create bunching at higher harmonics of the seed laser, then in an upstream undulator tuned to a higher harmonic of the seed one uses this bunching to radiate at that higher harmonic. For example starting with a 240 nm UV seed, one could "go to the eighth harmonic" and radiate in the second undulator at 30 nm XUV light. However from available UV seed(around 200 nm), one needs over one thousand harmonic number to reach X-ray wavelength range. Multiple stages HGHG scheme can be used repeatedly to achieve high order harmonic number (Cascade HGHG). Output radiation of one stage becomes the seed laser of the next stage. The total harmonic equals the product of harmonic numbers of each stage.
Medical applications At the 2006 annual meeting of the American Society for Laser Medicine and Surgery (ASLMS), Dr. Rox Anderson of the Wellman Laboratory of Photomedicine of Harvard Medical School and Massachusetts General Hospital reported on the possible medical application of the free electron laser. It was reported that at infrared wavelengths, water in tissue was heated by the laser, but at 915, 1210 and 1720 nm, subsurface lipids were differentially heated more strongly than water. The possible applications include the selective destruction of sebum lipids to treat acne, as well as targeting other lipids for the treatment of cellulite and atherosclerosis. [1] R. Rox Anderson, is an interdisciplinary researcher in photomedicine, the combination of the physics of light with medicine. ...
Harvard Medical School (HMS) is one of the graduate schools of Harvard University. ...
Massachusetts General Hospital (often abbreviated to Mass General or just MGH) is a teaching hospital of Harvard Medical School and biomedical research facility in Boston, Massachusetts. ...
Cellulite. ...
Military applications FEL is also considered by US Navy as a good candidate for anti-missile directed-energy weapon. Significant progress is being made in increasing FEL power levels (already at 10 kW, as demonstrated at the JLab FEL) and it should be possible to build compact multi-megawatt class FEL lasers (Airborne megawatt class free-electron laser for defense and security). The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ...
Directed-energy weapon refers to a type of weapon that emits energy in a particular direction by a means other than a projectile. ...
Thomas Jefferson National Accelerator Facility (TJNAF), commonly called Jefferson Lab (JLAB), is a U.S. national laboratory operated as of 1 June 2006 by Jefferson Science Associates, LLC, a joint venture between Southeastern Universities Research Association, Inc. ...
Patents - Brau, et al. U.S. Patent 4,189,686 "Combination free electron and gaseous laser", February 19, 1980.
- Brau, et al., U.S. Patent 4,287,488 , "Rf Feedback free electron laser", September 1, 1981.
- Gover, U.S. Patent 4,367,551 , "Electrostatic free electron laser", January 4, 1983.
- Brau, et al., U.S. Patent 4,442,522 , "Circular free-electron laser", April 10, 1984.
- Smith, et al., U.S. Patent 4,449,219 , "Free electron laser", May 15, 1984.
- Madey, U.S. Patent 4,479,219 , "Excitation cancelling free electron laser", October 23, 1984.
- Prosnitz, et al., U.S. Patent 4,506,229 "Free electron laser designs for laser amplification", March 19, 1985.
- Bhowmik, et al., U.S. Patent 4,698,815 , "Efficiency enhanced free electron laser", October 6, 1987.
- Brau, et al., U.S. Patent 4,479,218 , "Free electron laser using Rf coupled accelerating and decelerating structures", October 23, 1984
- Madey, et al., U.S. Patent 4,740,973 , "Free electron laser", April 26, 1988.
- Villa, U.S. Patent 4,972,420 , "Free electron laser", November 20, 1990.
- Szoke, et al., U.S. Patent 4,500,843 , "Multifrequency, single pass free electron laser", February 19, 1985.
- Madey, et al., U.S. Patent 6,636,534 , "Phase displacement free-electron laser", October 21, 2003.
See also The TESLA particle accelerator facility is located Hamburg, Germany. ...
Reflex klystron Type 2K25 or 723 A/B. The threaded adjustment rod on the right side allows the position of the reflector to be adjusted (by compressing the reflex cavity), and thus the natural resonant frequency of the device. ...
Further reading - Boscolo, et al., "Free-Electron Lasers and Masers on Curved Paths". Appl. Phys., (Germany), vol. 19, No. 1, pp. 46-51, May 1979.
- Deacon et al., "First Operation of a Free-Electron Laser". Phys. Rev. Lett., vol. 38, No. 16, Apr. 1977, pp. 892-894.
- Elias, et al., "Observation of Stimulated Emission of Radiation by Realistic Electrons in a Spatially Periodic Transverse Magnetic Field", Phys. Rev. Lett., 36 (13), 1976, p. 717.
- Gover, "Operation Regimes of Cerenkov-Smith-Purcell Free Electron Lasers and T. W. Amplifiers". Optics Communications, vol. 26, No. 3, Sep. 1978, pp. 375-379.
- Gover, "Collective and Single Electron Interactions of Electron Beams with Electromagnetic Waves and Free Electrons Lasers". App. Phys. 16 (1978), p. 121.
- "A Unified Theory of Magnetic Bremsstrahlung, Electrostatic Bremsstrahlung, Compton-Raman Scatering and Cerenkov-Smith-Purcell Free Electron Laser".
- "The FEL Program at Jefferson Lab" [2]
References New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ...
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