Synchrotron radiation is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e. when they are subject to an acceleration perpendicular to their velocity. It undulators and/or wigglers. If the particle is non-relativistic the emission is called cyclotron emission. If, on the other hand, the particles are relativistic, sometimes referred to as ultrarelativistic, the emission is called synchrotron emission. Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or by fast electrons moving through magnetic fields; the radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum, called continuum radiation. Syncradiation was named after its discovery in Schenectady, New York from a General Electric synchrotron accelerator built in 1946 and announced in May 1947 by Frank Elder, Anatole Gurewitsch, Robert Langmuir and Herb Pollock in a letter entitled "Radiation from Electrons in a Synchrotron".
Pollock recounts: On April 24, Langmuir and I were running the machine and as usual were trying to push the electron gun and its associated pulse transformer to the limit. Some intermittent sparking had occurred and we asked the technician to observe with a mirror around the protective concrete wall, he signaled to turn off the synchrotron as "he saw an arc in the tube." The vacuum was still excellent, so Langmuir and I came to the end of the wall and observed. At first we thought it might be due to Cherenkov radiation, but it soon became clearer that we were seeing Ivanenko and Pomeranchuk radiation. Broad Spectrum: the users can select the wavelength required for their experiment; when high-energy particles are in acceleration, including electrons forced to travel in a curved path by a magnetic field, synchrotron radiation is produced. This is similar to a radio antenna, but with the difference that, in theory, the relativistic speed will change the observed frequency due to the Doppler effect by the Lorentz factor, γ.
Relativistic length contraction bumps the frequency observed by another factor of γ, thus multiplying the GHz frequency of the resonant cavity that accelerates the electrons into the X-ray range. The radiated power is given by the relativistic Larmor formula while the force on the emitting electron is given by the Abraham–Lorentz–Dirac force; the radiation pattern can be distorted from an isotropic dipole pattern into an forward-pointing cone of radiation. Synchrotron radiation is the brightest artificial source of X-rays; the planar acceleration geometry appears to make the radiation linearly polarized when observed in the orbital plane, circularly polarized when observed at a small angle to that plane. Amplitude and frequency are however focused to the polar ecliptic. Synchrotron radiation may occur in accelerators either as a nuisance, causing undesired energy loss in particle physics contexts, or as a deliberately produced radiation source for numerous laboratory applications. Electrons are accelerated to high speeds in several stages to achieve a final energy, in the GeV range.
In the LHC proton bunches produce the radiation at increasing amplitude and frequency as they accelerate with respect to the vacuum field, propagating photoelectrons, which in turn propagate secondary electrons from the pipe walls with increasing frequency and density up to 7×1010. Each proton may lose 6.7 keV per turn due to this phenomenon. Synchrotron radiation is generated by astronomical objects where relativistic electrons spiral through magnetic fields. Two of its characteristics include non-thermal power-law spectra, polarization, it was first detected in a jet emitted by Messier 87 in 1956 by Geoffrey R. Burbidge, who saw it as confirmation of a prediction by Iosif S. Shklovsky in 1953, but it had been predicted earlier by Hannes Alfvén and Nicolai Herlofson in 1950. Solar flares accelerate particles that emit in this way, as suggested by R. Giovanelli in 1948 and described critically by J. H. Piddington in 1952. T. K. Breus noted that questions of priority on the history of astrophysical synchrotron radiation are complicated, writing: In particular, the Russian physicist V.
L. Ginzburg broke his relationships with I. S. Shklovsky and did not speak with him for 18 years. In the West, Thomas Gold and Sir Fred Hoyle were in dispute with H. Alfven and N. Herlofson, while K. O. Kiepenheuer and G. Hutchinson were ignored by them. Supermassive black holes have been suggested for producing synchrotron radiation, by ejection of jets produced by gravitationally accelerating ions through the super contorted'tubular' polar areas of magnetic fields; such jets, the nearest being in Messier 87, have been confirmed by the Hubble telescope as superluminal, travelling at 6 × c from our planetary frame. This phenomenon is caused because the jets are travelling near the speed of light and at a small angle towards the observer; because at every point of their path the high-velocity jets are emitting light, the light they emit does not approach the observer much more than the jet itself. Light emitted
Cuprate superconductors are high temperature superconductors made of cuprates. They are layered materials. Interest in cuprates increased in 1986 with the discovery of high-temperature superconductivity in the Non-stoichiometric cuprate lanthanum barium copper oxide La 2 − x Ba x CuO 4; the Tc for this material was 35 K, well above the previous record of 23K. Thousands of publications examine the superconductivity in cuprates between 1986 and 2001, Bednorz and Müller were awarded the Nobel Prize in Physics only a year after their discovery. From 1986 to 2008, many cuprate superconductors were identified, the most famous being yttrium barium copper oxide. Another example is bismuth strontium calcium copper oxide with Tc = 95–107 K depending on the n value. Thallium barium calcium copper oxide was the next class of high-Tc cuprate superconductors with Tc = 127 K observed in Tl2Ba2Ca2Cu3O10 in 1988; the highest confirmed, ambient-pressure, Tc is 135 K, achieved in 1993 with the layered cuprate HgBa2Ca2Cu3O8+x.
Few months another team measured superconductivity above 150K in the same compound under applied pressure. Cuprate superconductors feature copper oxides in both the oxidation state 3+ as well as 2+. For example, YBa2Cu3O7 is described as Y3+227. All superconducting cuprates are layered materials having a complex structure described as a superlattice of superconducting CuO2 layers separated by spacer layers where the misfit strain between different layers and dopants in the spacers induce a complex heterogeneity that in the superstripes scenario is intrinsic for high temperature superconductivity. BSCCO superconductors have large-scale applications. For example, tens of kilometers of BSCCO-2223 superconductive tape are being used in the current leads of the Large Hadron Collider
In electrodynamics, linear polarization or plane polarization of electromagnetic radiation is a confinement of the electric field vector or magnetic field vector to a given plane along the direction of propagation. See polarization and plane of polarization for more information; the orientation of a linearly polarized electromagnetic wave is defined by the direction of the electric field vector. For example, if the electric field vector is vertical the radiation is said to be vertically polarized; the classical sinusoidal plane wave solution of the electromagnetic wave equation for the electric and magnetic fields is E =∣ E ∣ R e B = z ^ × E / c for the magnetic field, where k is the wavenumber, ω = c k is the angular frequency of the wave, c is the speed of light. Here ∣ E ∣ is the amplitude of the field and | ψ ⟩ = d e f = is the Jones vector in the x-y plane; the wave is linearly polarized when the phase angles α x, α y are equal, α x = α y = d e f α. This represents. In that case, the Jones vector can be written | ψ ⟩ = exp .
The state vectors for linear polarization in x or y are special cases of this state vector. If unit vectors are defined such that | x ⟩ = d e f and | y ⟩ = d e f the polarization state can be written in the "x-y basis" as | ψ ⟩ = cos θ exp | x ⟩ + sin θ exp | y ⟩ = ψ x | x ⟩ + ψ y | y ⟩. Sinusoidal plane-wave solutions of the electromagnetic wave equation Polarization Circular polarization Elliptical polarization Plane of polarization Photon polarization Jackson, John D.. Classical Electrodynamics. Wiley. ISBN 0-471-30932-X. Animation of Linear Polarization Comparison of Linear Polarization with Circular and Elliptical Polarizations This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C"
X-ray photoelectron spectroscopy
X-ray photoelectron spectroscopy is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand range, empirical formula, chemical state and electronic state of the elements that exist within a material. Put more XPS is a useful measurement technique because it not only shows what elements are within a film but what other elements they are bonded to; this means if you have a metal oxide and you want to know if the metal is in a +1 or +2 state, using XPS will allow you to find that ratio. However at most the instrument will only probe 20nm into a sample. XPS spectra are obtained by irradiating a material with a beam of X-rays while measuring the kinetic energy and number of electrons that escape from the top 0 to 10 nm of the material being analyzed. XPS requires high vacuum or ultra-high vacuum conditions, although a current area of development is ambient-pressure XPS, in which samples are analyzed at pressures of a few tens of millibar.
XPS can be used to analyze the surface chemistry of a material in its as-received state, or after some treatment, for example: fracturing, cutting or scraping in air or UHV to expose the bulk chemistry, ion beam etching to clean off some or all of the surface contamination or to intentionally expose deeper layers of the sample in depth-profiling XPS, exposure to heat to study the changes due to heating, exposure to reactive gases or solutions, exposure to ion beam implant, exposure to ultraviolet light. XPS is known as ESCA, an abbreviation introduced by Kai Siegbahn's research group to emphasize the chemical information that the technique provides. In principle XPS detects all elements. In practice, using typical laboratory-scale X-ray sources, XPS detects all elements with an atomic number of 3 and above, it cannot detect hydrogen or helium. Detection limits for most of the elements are in the parts per thousand range. Detection limits of parts per million are possible, but require special conditions: concentration at top surface or long collection time.
XPS is used to analyze inorganic compounds, metal alloys, polymers, catalysts, ceramics, papers, woods, plant parts, make-up, bones, medical implants, bio-materials, viscous oils, ion-modified materials and many others. XPS is less used to analyze the hydrated forms of some of the above materials by freezing the samples in their hydrated state in an ultra pure environment, allowing or causing multilayers of ice to sublime away prior to analysis; such hydrated XPS analysis allows hydrated sample structures, which may be different from vacuum-dehydrated sample structures, to be studied in their more relevant as-used hydrated structure. Many biomaterials such as hydrogels are examples of such samples. XPS is used to measure: elemental composition of the surface empirical formula of pure materials elements that contaminate a surface chemical or electronic state of each element in the surface uniformity of elemental composition across the top surface uniformity of elemental composition as a function of ion beam etching XPS can be performed using a commercially built XPS system, a built XPS system, or a synchrotron-based light source combined with a custom-designed electron energy analyzer.
Commercial XPS instruments in the year 2005 used either a focused 20- to 500-micrometer-diameter beam of monochromatic Al Kα X-rays, or a broad 10- to 30-mm-diameter beam of non-monochromatic Al Kα X-rays or Mg Kα X-rays. A few specially designed XPS instruments can analyze volatile liquids or gases, or materials at pressures of 1 torr, but there are few of these types of XPS systems; the ability to heat or cool the sample during or prior to analysis is common. Because the energy of an X-ray with particular wavelength is known, because the emitted electrons' kinetic energies are measured, the electron binding energy of each of the emitted electrons can be determined by using an equation, based on the work of Ernest Rutherford: E binding = E photon − where Ebinding is the binding energy of the electron, Ephoton is the energy of the X-ray photons being used, Ekinetic is the kinetic energy of the electron as measured by the instrument and ϕ is the work function dependent on both the spectrometer and the material.
This equation is a conservation of energy equation. The work function term ϕ is an adjustable instrumental correction factor that accounts for the few eV of kinetic energy given up by the photoelectron as it becomes absorbed by the instrument's detector, it is a constant that needs to be adjusted in practice. In 1887, Heinrich Rudolf Hertz discovered but could not explain the photoelectric effect, explained in 1905 by Albert Einstein. Two years after Einstein's publication, in 1907, P. D. Innes experimented with a Röntgen tube, Helmholtz coils, a magnetic field hemisphere, photographic plates, to record broad bands of emitted elect
Angle-resolved photoemission spectroscopy
Angle-resolved photoemission spectroscopy, is a direct experimental technique to observe the distribution of the electrons in the reciprocal space of solids. The technique is a refinement of ordinary photoemission spectroscopy, studying photoemission of electrons from a sample achieved by illumination with soft X-rays. ARPES is one of the most direct methods of studying the electronic structure of the surface of solids. ARPES gives information on the direction and scattering process of valence electrons in the sample being studied; this means that information can be gained on both the energy and momentum of an electron, resulting in detailed information on band dispersion and Fermi surface. The technique is known as ARUPS when using ultraviolet light to generate photoemission. Band mapping, in condensed matter physics refers to the process which allows for detection of photoelectrons emitted from an observed surface at different emission angles; this process is employed in ARPES. ARPES is used to investigate the electronic structure of solid surfaces and interfaces.
By employing the band mapping process, several fundamental physical properties of a solid can be determined. The properties which can be determined using this process include the following: Kinetic energy of the electron; the electronic states in the solid are described by energy bands, which have associated energy band dispersions E — energy eigenvalues for delocalized electrons in a crystalline medium according to Bloch's theorem. Band mapping has an advantage over optical spectroscopy. In the latter, only the energy-band separations at various optical critical points in k-space — energy between the initial and final states — are determined. ARPES, on the other hand, provides information about the absolute location of energy bands at different values of k relative to the Fermi level. From conservation of energy, we have E = ℏ ω − E B − ϕ where ℏ ω is the incoming photon energy — measured E is the kinetic energy of the outgoing electron — measured E B is the binding energy of the electron ϕ is the electron work function Photon momentum is neglected because of its small contribution compared with electron momentum.
In the typical case, where the surface of the sample is smooth, translational symmetry requires that the component of electron momentum in the plane of the sample be conserved: ℏ k i ∥ = ℏ k ∥ = 2 m E sin θ where ℏ k is the momentum of the outgoing electron — measured by angle ℏ k i is the initial momentum of the electronHowever, the normal component of electron momentum k i ⊥ might not be conserved. The typical way of dealing with this is to assume that the final in-crystal states are free-electron-like, in which case one has k i ⊥ = 1 ℏ 2 m in which V 0 denotes the band depth from vacuum, including electron work function ϕ; the equations for energy and momentum can be solved to determine the dispersion relation between the binding energy, E B, the wave vector, k i = k i ∥ + k i ⊥, of the electron. Electronic band structure Felix Bloch Laser-based angle-resolved photoemission spectroscopy Resonance Raman spectroscopy Two-photon photoelectron spectroscopy Park, Jongik. "Photoemission study of the rare earth intermetallic compounds: RNi2Ge2."
2004, Iowa State University, Iowa Andrea Damascelli, "Probing the Electronic Structure of Complex Systems by ARPES", Physica Scripta T109, 61-74 Angle-resolved photoemission spectroscopy of the cuprate superconductors ARPES experiment in fermiology of quasi-2D metals
In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electric field of the wave has a constant magnitude but its direction rotates with time at a steady rate in a plane perpendicular to the direction of the wave. In electrodynamics the strength and direction of an electric field is defined by its electric field vector. In the case of a circularly polarized wave, as seen in the accompanying animation, the tip of the electric field vector, at a given point in space, describes a circle as time progresses. At any instant of time, the electric field vector of the wave describes a helix along the direction of propagation. A circularly polarized wave can be in one of two possible states, right circular polarization in which the electric field vector rotates in a right-hand sense with respect to the direction of propagation, left circular polarization in which the vector rotates in a left-hand sense. Circular polarization is a limiting case of the more general condition of elliptical polarization.
The other special case is the easier-to-understand linear polarization. The phenomenon of polarization arises as a consequence of the fact that light behaves as a two-dimensional transverse wave. On the right is an illustration of the electric field vectors of a circularly polarized electromagnetic wave; the electric field vectors have a constant magnitude but their direction changes in a rotary manner. Given that this is a plane wave, each vector represents the magnitude and direction of the electric field for an entire plane, perpendicular to the axis. Given that this is a circularly polarized plane wave, these vectors indicate that the electric field, from plane to plane, has a constant strength while its direction rotates. Refer to these two images in the plane wave article to better appreciate this; this light is considered to be right-hand, clockwise circularly polarized. Since this is an electromagnetic wave each electric field vector has a corresponding, but not illustrated, magnetic field vector, at a right angle to the electric field vector and proportional in magnitude to it.
As a result, the magnetic field vectors would trace out a second helix. Circular polarization is encountered in the field of optics and in this section, the electromagnetic wave will be referred to as light; the nature of circular polarization and its relationship to other polarizations is understood by thinking of the electric field as being divided into two components which are at right angles to each other. Refer to the second illustration on the right; the vertical component and its corresponding plane are illustrated in blue while the horizontal component and its corresponding plane are illustrated in green. Notice that the rightward horizontal component leads the vertical component by one quarter of a wavelength, it is this quadrature phase relationship which creates the helix and causes the points of maximum magnitude of the vertical component to correspond with the points of zero magnitude of the horizontal component, vice versa. The result of this alignment is that there are select vectors, corresponding to the helix, which match the maxima of the vertical and horizontal components.
To appreciate how this quadrature phase shift corresponds to an electric field that rotates while maintaining a constant magnitude, imagine a dot traveling clockwise in a circle. Consider how the vertical and horizontal displacements of the dot, relative to the center of the circle, vary sinusoidally in time and are out of phase by one quarter of a cycle; the displacements are said to be out of phase by one quarter of a cycle because the horizontal maximum displacement is reached one quarter of a cycle before the vertical maximum displacement is reached. Now referring again to the illustration, imagine the center of the circle just described, traveling along the axis from the front to the back; the circling dot will trace out a helix with the displacement toward our viewing left, leading the vertical displacement. Just as the horizontal and vertical displacements of the rotating dot are out of phase by one quarter of a cycle in time, the magnitude of the horizontal and vertical components of the electric field are out of phase by one quarter of a wavelength.
The next pair of illustrations is that of left-handed, counter-clockwise circularly polarized light when viewed by the receiver. Because it is left-handed, the rightward horizontal component is now lagging the vertical component by one quarter of a wavelength rather than leading it. To convert a given handedness of polarized light to the other handedness one can use a half-waveplate. A half-waveplate shifts a given linear component of light one half of a wavelength relative to its orthogonal linear component; the handedness of polarized light is reversed when it is reflected off a surface at normal incidence. Upon such reflection, the rotation of the plane of polarization of the reflected light is identical to that of the incident field. However, with propagation now in the opposite direction, the same rotation direction that would be described as "right handed" for the incident beam, is "left-handed" for propagation in the reverse direction, vice versa. Aside from the reversal of handedness, the ellipticity of polarization is preserved.
Note that this principle only holds for light reflected at normal incidence. For instance, right circularly polarized light reflected from a dielectric surface at grazing incidence will st
Barium borate is an inorganic compound, a borate of barium with a chemical formula BaB2O4 or Ba2. It is available as a hydrate or dehydrated form, as white colorless crystals; the crystals exist in the high-temperature α phase and low-temperature β phase, abbreviated as BBO. Barium borate exists in two major crystalline forms: alpha and beta; the low-temperature beta phase converts into the alpha phase upon heating to 925 °C. β-Barium borate differs from the α form by the positions of the barium ions within the crystal. Both phases are birefringent, however the α phase possesses centric symmetry and thus does not have the same nonlinear properties as the β phase. Alpha barium borate, α-BaB2O4 is an optical material with a wide optical transmission window from about 190 nm to 3500 nm, it has good mechanical properties and is a suitable material for high-power ultraviolet polarization optics. It can replace calcite, titanium dioxide or lithium niobate in Glan–Taylor prisms, Glan–Thompson prisms, walk-off beam splitters and other optical components.
It has low hygroscopicity, its Mohs hardness is 4.5. Its damage threshold is 500 MW/cm2 at 355 nm. Beta barium borate, β-BaB2O4, is a nonlinear optical material transparent in the range ~190–3300 nm, it can be used for spontaneous parametric down-conversion. Its Mohs hardness is 4.5. Barium borate has strong negative uniaxial birefringence and can be phase-matched for type I second-harmonic generation from 409.6 to 3500 nm. The temperature sensitivity of the indices of refraction is low, leading to an unusually large temperature phase-matching bandwidth. Barium borate can be prepared by reaction of an aqueous solution of boric acid with barium hydroxide; the prepared γ-barium borate contains water of crystallization that can not be removed by drying at 120 °C. Dehydrated γ-barium borate can be prepared by heating to 300–400 °C. Calcination at about 600–800 °C causes complete conversion to the β form. BBO prepared by this method does not contain trace amounts of BaB2O2BBO crystals for nonlinear optics can be grown from fluxed melt of barium borate, sodium oxide and sodium chloride.
Thin films of barium borate can be prepared by MOCVD from barium hydro-triborate. Different phases can be obtained depending on deposition temperatures. Thin films of beta-barium borate can be prepared by sol-gel synthesis. Barium borate monohydrate is prepared from the solution of barium sodium tetraborate, it is a white powder. It is used as an additive to e.g. paints as flame retardant, mold inhibitor, corrosion inhibitor. It is used as a white pigment. Barium borate dihydrate is prepared from the solution of sodium metaborate and barium chloride at 90–95 °C. After cooling to room temperature, white powder is precipitated. Barium borate dihydrate loses water at above 140 °C, it is used as a flame retardant for paints and paper. BBO is a popular nonlinear optical crystal. Quantum linked. Barium borate is a fungicide, it is added to paints, adhesives and paper products. Barium borate is resistant to ultraviolet radiation, it can act as UV stabilizer for polyvinyl chloride. The solubility of barium borate is a disadvantage.
Silica-coated powders are available. The alkaline properties and the anodic passivation properties of the borate ion enhance the anticorrosion performance. Available barium metaborate pigment comes in three grades. Barium borate shows synergistic performance with zinc borate. Barium borate is used as a flux in some barium titanate and lead zirconate EIA Class 2 dielectric ceramic formulations for ceramic capacitors, in amount of about 2%; the barium-boron ratio is critical for flux performance. Barium borate-fly ash glass can be used as radiation shielding; such glasses are superior in performance to concrete and to other barium borate glasses