Coherent X-ray diffraction radiation produced by microbunched beams passing close to the edge of a slab

With use of formulas for single-particle X-ray transition and diffraction radiation (XTR and XDR), we obtain expressions for spectral-angular distributions and total numbers of emitted quanta in coherent X-ray transition radiation (CXTR2) and coherent X-ray diffraction radiation (CXDR) arising when a microbunched beam of electrons, respectively, intersects the interfaces of a slab or flies at small distance from the edge of the slab. Comparison of obtained results with those known for CXTR from a single interface is performed. It is shown on the basis of numerical calculations that experimental study of CXDR is at present possible on the Linac Coherent Light Source (LCLS, SLAC).     

Study of the surface and far fields of terahertz radiation generated by large-aperture photoconductive antennas

We have studied analytically the temporal characteristics of terahertz radiation emitted from a biased largeaperture photoconductive antenna triggered by an ultrashort optical pulse. We have included the effects of the finite lifetime and transient mobility dynamics of photogenerated carriers in the analysis. Succinct explicit expressions are obtained for the emitted radiation in the surface field and in the far field. The dependence of the waveforms of the radiated field on the fluence and duration of triggering optical pulse, carrier relaxation time and carrier lifetime are discussed in detail using the obtained expressions.     

On the role of substrate in light-harvesting experiments

An analysis of the emitted light distribution for a single emitter located at the planar interface of two optical media was performed. The interface of a varying refractive index substrate with air was considered, which is a common case in luminescence microscopy (spectroscopy) experiments. A modification of the radiative recombination rate induced by the variation of the substrate together with the emitted radiation spatial redistribution were taken into account. Simulation results show that the collection efficiency of the emitted light can vary several times depending on the substrate choice and the emitter intrinsic quantum efficiency.     

Transition radiation from a relativistic electron obliquely incident on a thin metal plate of finite transverse dimensions

The problem of transition radiation generated by the oblique motion of a relativistic electron through a thin metal plate of finite transverse dimensions is considered. The expressions for the spectral and angular densities of radiation emitted forward and backward are obtained. It is shown that, in the millimeter and the submillimeter range, the spectra of both forward and backward radiation for targets of finite transverse dimensions can differ substantially from the corresponding spectra for an infinite plate.     

Transition radiation of a charge in media with a nonuniform potential

The influence of a potential barrier on the transition radiation in the form of volume and surface electromagnetic waves emitted by a charged particle crossing an interface between media is investigated. It is shown that the volume-wave radiation field arises not only as a result of the jump in the dielectric constant at the boundary but also as a result of the velocity jump and the reflection of an electron induced by the presence of a nonuniform potential barrier. The angular distribution of the transition radiation intensity is obtained. Zh. Tekh. Fiz. 68, 11–14 (January 1998)     

The spectral maximum of synchrotron radiation

A three-level system is considered as a simplest example where a possibility of solving the spectral problem is observed. We thoroughly analyze the relation between the amount of radiation emitted by the particle during the transitions to the first excited state and to the ground state. Generalizing basic expressions we can follow the evolution of spectral maximum. It turns out there is a condition for radiation maximum to stay at highest harmonic.     

Impact ionization effects at interfaces between solid dielectrics and insulating oil or air,during high voltage pulse applications

In this paper, an investigation of the impact ionization effects at interfaces between common industrial solid dielectrics and air or insulating oil, under the application of strong, fast rising electric fields (dF/dt10¹⁴ V m^-1s^-1), is presented. In the prebreakdown stages, the outbreak of partial discharges at an interface may come as the result of impact ionization and plays a very important role in the dielectric aging procedure. Experimental results show that the threshold electric field for the onset of partial discharges is considerably lower in the case of a solid dielectric-air interface, than the corresponding one in the case of a solid dielectric-oil interface. In addition, it is experimentally confirmed that an electromagnetic radiation is emitted. The spectral distribution of this radiation was found to extend up to the ultraviolet region, during the experiments.     

Transition radiation of elastic waves at the interface of two elastic half-planes

Radiation of elastic waves is studied that is emitted by a point load that crosses the interface of two elastic half-planes. It is assumed that the load has a constant magnitude, moves along a straight line normal to the interface, and has a constant speed that is smaller than the minimum shear wave speed in the half-planes. In this case the mechanism of excitation of elastic waves is conventionally referred to as transition radiation. The adopted model allows to obtain an analytical expression for the elastic field excited by the load in the frequency-wavenumber domain. Using this expression, the energy of transition radiation is derived in a closed form. It is shown that transition radiation of the body waves occurs at any non-zero velocity of the load. Additionally, transition radiation of interface waves may occur provided that parameters of the half-planes allow existence of Stoneley waves. A parametric analysis of the directivity diagram of radiated body waves is accomplished focusing on dependence of the diagram on the load speed, load direction, and parameters of the half-planes. Using parameters that allow radiation of interface waves, the energy of this radiation is compared to that of the body waves. It is shown that the energy of the interface waves is greater unless the load velocity is close to the lowest body wave velocity.     

New method for determining refractive index and thickness of fluorescent thin films

The optical parameters of homogeneous, isotropic, and fluorescent thin films are determined by comparing measured with calculated angular intensity distributions of the s- and p-polarized light emitted into the substrate. The method also yields information about the multipole nature of the emitted radiation. The theory is presented for electric and magnetic dipole transitions. For extremely thin layers of optical thickness n₀d₀ ? λ/8 (where λ is the emission wavelength) analytic expressions for the angular intensity distributions are given. For between 25–30 nm thick evaporated layers of an europium-benzoyltrifluoro-acetone- chelate the refractive index was determined to be n₀ = 1.57 at λ = 612 nm. The fluorescent light emitted by these layers in an about 6 nm wide band centered at λ = 612 nm is emitted by randomly oriented electric dipoles.     

MOS结构电离辐射效应模型研究

基于氧化层空穴俘获和质子诱导界面陷阱电荷形成物理机制的分析,分别建立了MOS结构电离辐射诱导氧化层陷阱电荷密度、界面陷阱电荷密度与辐射剂量相关性的物理模型.由模型可以得到,在低剂量辐照条件下辐射诱导产生的两种陷阱电荷密度与辐射剂量成线性关系,在中到高辐射剂量下诱导陷阱电荷密度趋于饱和,模型可以很好地描述这两种陷阱电荷与辐射剂量之间的关系.最后讨论了低剂量辐照下,两种辐射诱导陷阱电荷密度之间的关系,认为低辐射剂量下两者存在线性关系,并用实验验证了理论模型的正确性.该模型为辐射环境下MOS器件辐射损伤提供了更 关键词： MOS结构 辐射 界面陷阱 氧化层陷阱     

Cherenkov radiation in biaxial crystals—I

The radiation emitted by a uniformly moving point charge in a biaxial crystal is studied by a new method. Fourier integrals for the field are set up for the general case without imposing any restriction on the dielectric and magnetic properties of the crystal or on the direction of motion of the charge. In the case of motion along a principal dielectric axis the integrals are evaluated exactly and closed expressions for the radiated energy are obtained. For radiation of either kind these expressions involve Heuman's Lambda function and the complete elliptic integral of the first kind.     

On transition radiation

Summary A treatment of transition radiation between two dielectric media is presented which is based on the exact expressions for the fields of the particle in the two media. Expressions for the spectral distribution of the energy emitted forward and for that emitted backward are derived. The results are in accord with experimental findings for ultra-relativistic particles. In the asymptotic region the energy spectrum becomes discrete. It is indicated how the treatment can be extended to the case of a plate and to that of a wave guide, as well as to emission by a monopole. The case of the simultaneous emission of transition radiation and Čerenkov radiation is considered and the relationship between them is clarified. In particular, it is shown that, when the particle can emit Čerenkov radiation in the forward medium, it will also emit an interference signal. This is several orders of magnitude smaller than the usual transition radiation and is concentrated in the forward direction. It is also found that the Čerenkov wave emitted by the particle in the backward medium will be partially reflected and partially refracted into the forward medium, after the particle crosses the boundary between the two media. The linear energy density for the refracted wave is calculated and it is shown that under certain feasible conditions this is amenable to experimental verification. This work was done while the author was a summer visitor at Stanford Linear Accelerator Center, Stanford University. It was supported by the U.S. Department of Energy, contract DE-AC03-76SF00515.     

Vertical distribution of traffic noise—A preliminary study

This paper examines the effect of flight on the sound radiated by a high frequency source embedded in a constant area jet pipe in the presence of flow. Ray acoustics theory and classical results for sound transmission at an interface of relative motion are used. The diffraction of sound at the nozzle lips, the inhomogeneity and irregularity of the interface and the possibility of instability waves being triggered by the incident sound are neglected. Some of the waves characterized by wave-fronts pointing upstream are shown to be convected downstream by the flow and to illuminate the forward arc after refraction at the jet interface. The amount of energy emitted by the source, which is trapped inside the flow, depends only on internal jet pipe conditions. However, the portion of the forward arc which is illuminated by this energy, is a function of flight speed. The radiation into the ambient atmosphere at rest of a basically omnidirectional source peaks at the edge of the downstream zone of silence and falls off rapidly when the observation angle is increased. The flight to static comparison reveals an interesting forward arc amplification due to flight but this occurs in a range of angles where the radiation is basically rather feeble.     

Spontaneous emission from a semi-bounded plasma

The electromagnetic radiation field of sources arbitrarily distributed throughout space is found for the case of a semi-bounded plasma when the charged plasma particles are specularly and randomly scattered by the plasma interface. The spectral distributions of the thermal radiation emitted by a nonisothermal semi-bounded plasma into an external medium having a nonzero temperature are calculated.Institute of Theoretical Physics, Ukrainian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, No. 10, pp. 1237–1261, October, 1994.     

Quasi-linear stage of synchrotron instability. II. Monoenergetic initial electron distribution

Using the results obtained in the first part of the work, we analyze quasi-linear relaxation of an initial monoenergetic quasi-isotropic electron distribution embedded in a cold plasma. It is shown that in this case the radiation energy density increases due to synchrotron instability only at the initial stage of relaxation and after that reabsorption emerges. At the stage of reabsorption, electrons absorb the emitted radiation for the same characteristic time as the time of radiation energy density increase at the maser stage. We calculate the maximum fraction of initial electron energy which is converted into synchrotron radiation energy. Analytical expressions are obtained for the amplitude and width of the frequency spectrum at the instant of the maximum level of synchrotron radiation and for the maximum value and width of the electron distribution over momentum at the end of relaxation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radio.zika, Vol. 49, No. 12, pp. 1063–1074, December 2006.     

Transmission of low-frequency sound through the water-to-air interface

L.M. Brekhovskikh revealed and studied the important role played by inhomogeneous waves emitted by a point source when they pass through an interface with a medium in which the velocity of sound is lower, for example, from water to air. This paper studies the energy characteristics of sound emitted into air by an underwater point source. The energy transfer due to inhomogeneous waves is shown to cause the phenomenon of anomalous transparency of the interface for low-frequency sound. The anomalous transparency manifests itself in that the energy flux through the interface increases with decreasing frequency of sound and, at sufficiently low frequencies, almost all of the acoustic energy produced by the underwater source is emitted into air. Conversely, at high frequencies, when the contribution of the inhomogeneous waves becomes negligible, the water-to-air interface is similar to a perfectly reflecting surface and almost all of the acoustic energy produced by the source is emitted into water. The anomalous transparency phenomenon changes the conventional opinion on the possibility of acoustic coupling between points in water and air and on the role played by physical processes evolving in the water column in generating atmospheric acoustic noise.     

Vertical component of the extremely low-frequency electric field excited by the grounded horizontal dipole

A representation of the vertical component of the electric field emitted by the grounded linear dipole is obtained in the form of an integral of an oscillating function and a method of its numerical integration is described. For the particular case in which the medium under the antenna is homogeneous and the field is calculated on the interface, the function obtained is transformed with the help of the Fock integrals to the form convenient for deriving simple approximate formulas and for analyzing the field behavior. Calculations performed by the expressions obtained corroborate the theoretical results.     

Frequency modulation of fluxon oscillations

The effect of the application of an ac external electromagnetic field to a long Josephson junction is studied by analyzing the spectrum of the radiation emitted by the junction. In the absence of the external field the junction, biased on a dc current singularity of the current-voltage characteristic, emits radiation at a frequency ƒ₀ in the X-band of the microwaves. The application of an external ac field having a frequency ƒ_m of the order of several megahertz gives rise to the appearance of spectral components at frequencies ƒ₀±nƒ_m, with n integer. The experimental results are described reasonably well by classical FM modulation theory.     

Tamm-Frank equation derived from expressions for transient radiation

The expressions for transient radiation intensity are analyzed in the case of a plane interface when the condition of Cerenkov radiation is satisfied. It is shown that they include the expression for Vavilov-Cerenkov radiation in a transparent medium modified by the interface. Institute of Physical Research, Armenian National Academy of Sciences, Ashtarak. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 9, pp. 1126–1144, September, 1997.     

The influence of quantum interference effects on the resonance fluorescence spectra of a degenerate three-level atom

The resonance fluorescence spectra of a degenerate three-level atom of the V-type in the field of an intense monochromatic wave with an arbitrary polarization composition are investigated. Analytical expressions are derived for the resonance fluorescence spectra, and the angular distribution of spontaneous fluorescence of atoms is analyzed for the D-line emitted by vapors of alkali atoms. It is shown that the number of lines in the spectrum may decrease in the case of the linear polarization of spontaneous radiation. The radiation relaxation operator is obtained for the D-line of alkali metals in the case when an atom is near the metal surface. Interference effects for such systems are analyzed.