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Gamma-ray Laser
A gamma-ray laser, or graser, is a hypothetical device that would produce coherent gamma rays, just as an ordinary laser produces coherent rays of visible light. Potential applications for gamma-ray lasers include medical imaging, spacecraft propulsion, and cancer treatment. In his 2003 Nobel lecture, Vitaly Ginzburg cited the gamma-ray laser as one of the 30 most important problems in physics. The effort to construct a practical gamma-ray laser is interdisciplinary, encompassing quantum mechanics, nuclear and optical spectroscopy, chemistry, solid-state physics, and metallurgy—as well as the generation, moderation, and interaction of neutrons—and involves specialized knowledge and research in all these fields. The subject involves both basic science and engineering technology. Research The problem of obtaining a sufficient concentration of resonant excited (isomeric) nuclear states for collective stimulated emission to occur turns on the broadening of the gamma- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity Laser
A gravity laser, also sometimes referred to as a Gaser, Graser, or Glaser, is a hypothetical device for stimulated emission of coherent gravitational radiation or gravitons, much in the same way that a standard laser produces coherent electromagnetic radiation. Principle of function While photons exist as excitations of a vector potential and so contain an oscillating dipole term, gravitons are a spin-2 field and so have an oscillating quadrupole term. For efficient lasing to occur, there are several conditions that must be met: # There must be particles in an excited state capable of emitting radiation at the desired frequency. In a normal laser, these would be valence electrons in an excited state. For a gaser, the more straightforward analog would be a binary system of massive bodies. # These particles must couple to supplied radiation, in order to provide stimulated emission. This could be possible in a gaser by a stimulated analog of the Penrose process. # The particles must ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homogeneous Broadening
Homogeneous broadening is a type of emission spectrum broadening in which all atoms radiating from a specific level under consideration radiate with equal opportunity. If an optical emitter (e.g. an atom) shows homogeneous broadening, its spectral linewidth is its natural linewidth, with a Lorentzian profile. Broadening in laser systems Broadening in laser physics is a physical phenomenon that affects the spectroscopic line shape of the laser emission profile. The laser emission is due to the (excitation and subsequent) relaxation of a quantum system (atom, molecule, ion, etc.) between an excited state (higher in energy) and a lower one. These states can be thought of as the eigenstates of the energy operator. The difference in energy between these states is proportional to the frequency/wavelength of the photon emitted. Since this energy difference has a fluctuation, then the frequency/wavelength of the "macroscopic emission" (the beam) will have a certain width (i.e. it will be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laser Types
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light which is ''coherent''. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar (light detection and ranging). Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of light w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground-state
The ground state of a quantum mechanics, quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. In quantum field theory, the ground state is usually called the vacuum state or the vacuum#The quantum-mechanical vacuum, vacuum. If more than one ground state exists, they are said to be degenerate energy level, degenerate. Many systems have degenerate ground states. Degeneracy occurs whenever there exists a unitary operator that acts non-trivially on a ground state and commutator, commutes with the Hamiltonian (quantum mechanics), Hamiltonian of the system. According to the third law of thermodynamics, a system at absolute zero temperature exists in its ground state; thus, its entropy is determined by the degeneracy of the ground state. Many systems, such as a perfect crystal lattice, have a unique ground state and ther ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neutron Capture
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, which are repelled electrostatically. Neutron capture plays a significant role in the cosmic nucleosynthesis of heavy elements. In stars it can proceed in two ways: as a rapid process (r-process) or a slow process (s-process). Nuclei of masses greater than 56 cannot be formed by thermonuclear reactions (i.e., by nuclear fusion) but can be formed by neutron capture. Neutron capture on protons yields a line at 2.223 MeV predicted and commonly observed in solar flares. Neutron capture at small neutron flux At small neutron flux, as in a nuclear reactor, a single neutron is captured by a nucleus. For example, when natural gold (197Au) is irradiated by neutrons (n), the isotope 198Au is formed in a highly excited state, and quickly deca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Pumped Laser
A nuclear pumped laser is a laser pumped with the energy of fission fragments. The lasing medium is enclosed in a tube lined with uranium-235 and subjected to high neutron flux in a nuclear reactor core. The fission fragments of the uranium create excited plasma with inverse population of energy levels, which then lases. Other methods, e.g. the He-Ar laser, can use the He(n,p)H reaction, the transmutation of helium-3 in a neutron flux, as the energy source, or employing the energy of the alpha particles. This technology may achieve high excitation rates with small laser volumes. Some example lasing media: * carbon dioxide * 3helium-argon * 3helium-krypton * 3helium-xenon Development Research in nuclear pumped lasers started in the early 1970s when researchers were unable to produce a laser with a wavelength shorter than 110 nm with the end goal of creating an x-ray laser. When laser wavelengths become that short the laser requires a huge amount of energy which must also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Excited State
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to an increase in energy level above a chosen starting point, usually the ground state, but sometimes an already excited state. The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that exhibit negative temperature). The lifetime of a system in an excited state is usually short: spontaneous or induced emission of a quantum of energy (such as a photon or a phonon) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the inverse of excitation. Long-lived excited states are often called ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiochemistry
Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being ''inactive'' as the isotopes are ''stable''). Much of radiochemistry deals with the use of radioactivity to study ordinary chemical reactions. This is very different from radiation chemistry where the radiation levels are kept too low to influence the chemistry. Radiochemistry includes the study of both natural and man-made radioisotopes. Main decay modes All radioisotopes are unstable isotopes of elements— that undergo nuclear decay and emit some form of radiation. The radiation emitted can be of several types including alpha, beta, gamma radiation, proton, and neutron emission along with neutrino and antiparticle emission decay pathways. 1. α (alpha) radiation—the emission of an alpha parti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Borrmann Effect
The Borrmann effect (or Borrmann–Campbell effect after Gerhard Borrmann and Herbert N. Campbell) is the anomalous increase in the intensity of X-rays transmitted through a crystal when it is being set up for Bragg reflection. The Borrmann effect—a dramatic increase in transparency to X-ray beams—is observed when X-rays satisfying Bragg's law diffract through a perfect crystal. The minimization of absorption seen in the Borrmann effect has been explained by noting that the electric field of the X-ray beam approaches zero amplitude at the crystal planes, thus avoiding the atoms. References * *{{cite journal , last1=Pettifer , first1=Robert F. , first2=Stephen P. , last2=Collins , first3=David , last3=Laundy , year=2009 , title=Quadrupole transitions revealed by Borrmann spectroscopy , journal=Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillating force is applied at a resonant frequency of a dynamic system, the system will oscillate at a higher amplitude than when the same force is applied at other, non-resonant frequencies. Frequencies at which the response amplitude is a relative maximum are also known as resonant frequencies or resonance frequencies of the system. Small periodic forces that are near a resonant frequency of the system have the ability to produce large amplitude oscillations in the system due to the storage of vibrational energy. Resonance phenomena occur with all types of vibrations or waves: there is mechanical resonance, orbital resonance, acoustic resonance, electromagnetic resonance, nuclear magnetic resonance (NMR), electron spin resonance (ESR) and reso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gain (laser)
In laser physics, gain or amplification is a process where the medium transfers part of its energy to the emitted electromagnetic radiation, resulting in an increase in optical power. This is the basic principle of all lasers. Quantitatively, ''gain'' is a measure of the ability of a laser medium to increase optical power. Definition The gain can be defined as the derivative of logarithm of power ~P~ as it passes through the medium. The factor by which an input beam is amplified by a medium is called the gain and is represented by G. :G = \frac\ln(P)=\frac where ~z~ is the coordinate in the direction of propagation. This equation neglects the effects of the transversal profile of beam. In the quasi-monochromatic paraxial approximation, the gain can be taken into account with the following equation : 2ik\frac= \Delta_E + 2 \nu E + i G E, where ~\nu~ is variation of index of refraction (Which is supposed to be small), ~E~ is complex field, related to the physical electric field ~ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emission Spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an electron making a atomic electron transition, transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances. Emission In physics, emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
