Transition radiation from an extended bunch of charged particles

The spatial distribution of the transition radiation generated by an extended system of charges is studied. The charges sequentially cross the interface at equispaced points. Also, the transition from a spherical bunch with the uniform charge distribution is considered. The radiation patterns produced by the point charge and by the bunch of the charges are shown to differ significantly at certain sizes of the bunch expressed in terms of the wavelength. Charge distributions such that the transition radiation exhibits the properties typical of the Doppler effect or of Vavilov-Cherenkov radiation are found to be possible.     

Peculiarities of the generation of Vavilov-Cherenkov radiation induced by a charged particle moving past a dielectric target

We consider Vavilov-Cherenkov radiation occurring as a result of uniform motion of a point charge in vacuum near a finite-size prismatic target with an arbitrary permittivity. The expression derived for the spectral-angular density of radiation contains a center of emission of Vavilov-Cherenkov radiation, which depends on the angle of flight of the point charge relative to the target. The results indicate that the main contribution to the formation of Vavilov-Cherenkov radiation comes from the polarization current occurring at the interface between the media.     

The mechanism of Vavilov-Cherenkov radiation

The mechanism of generation of Vavilov-Cherenkov radiation is discussed in this article. The developers of the theory of the Vavilov-Cherenkov effect, I.E. Tamm and I.M. Frank, attributed this effect to their discovery of a new mechanism of radiation when a charged particle moves uniformly and rectilinearly in the medium. As such a mechanism presupposes the violation of the laws of conservation of energy and momentum, they proposed the abolition of these laws to account for the Vavilov-Cherenkov radiation mechanism. This idea has received a considerably wide acceptance in the creation of other theories, for example, transition radiation theory. In this paper, the radiation mechanism for the charge constant motion is demonstrated to be incorrect, because it contradicts not only the laws of conservation of energy and momentum, but also the very definitions of uniform and rectilinear motion (Newton's First Law). A consistent explanation of the Vavilov-Cherenkov radiation microscopic mechanism that does not contradict the basic laws is proposed. It is shown that the radiation arises from the interaction of the moving charge with bound charges that are spaced fairly far away from its trajectory. The Vavilov-Cherenkov radiation mechanism bears a slowing down character, but it differs fundamentally from bremsstrahlung, primarily because the Vavilov-Cherenkov radiation onset results from a two-stage process. First, the moving particle polarizes the medium; then, the already polarized atoms radiate coherently, provided that the particle velocity exceeds the phase speed of light in the medium. If the particle velocity is less than the phase speed of light in the medium, the polarized atoms return energy to the outgoing particle. In this case, radiation is not observed. Special attention is given to the relatively constant particle velocity as the condition of the coherent composition of waves. However, its motion cannot be designated as a uniform and rectilinear one in the sense of its definition by Newton's First Law, and it also contradicts the laws of conservation of energy and momentum.     

Radiation from uniformly moving sources (Vavilov-Cherenkov effect,transition radiation,and some other phenomena)

The radiation produced by uniformly moving sources (the Vavilov-Cherenkov effect, the transition radiation, and some other phenomena) is discussed. This area of physical research originated in the Lebedev Physical Institute of the Russian Academy of Sciences and now represents an integral part of modern physics.     

Superluminal motion (review)

Prior to the development of Special Relativity, no restrictions were imposed on the velocity of the motion of particles and material bodies, as well as on energy transfer and signal propagation. At the end of the 19th century and the beginning of the 20th century, it was shown that a charge that moves at a velocity faster than the speed of light in an optical medium, in particular, in vacuum, gives rise to impact radiation, which later was termed the Vavilov-Cherenkov radiation. Shortly after the development of Special Relativity, some researchers considered the possibility of superluminal motion. In 1923, the Soviet physicist L.Ya. Strum suggested the existence of tachyons, which, however, have not been discovered yet. Superluminal motions can occur only for images, e.g., for so-called ??light spots,?? which were considered in 1972 by V.L. Ginzburg and B.M. Bolotovskii. These spots can move with a superluminal phase velocity but are incapable of transferring energy and information. Nevertheless, these light spots may induce quite real generation of microwave radiation in closed waveguides and create the Vavilov-Cherenkov radiation in vacuum. In this work, we consider various paradoxes, illusions, and artifacts associated with superluminal motion.     

Observation of Vavilov-Cherenkov radiation and EAS charged particles at large zenith angles

Extensive air showers (EASes) at zenith angles of 70–80 degrees with Vavilov-Cherenkov radiation having two and three maxima were registered at the Tian Shan Mountain Station of the Lebedev Physical Institute. In each such event, the subsequent maxima came with a time delay of 100 or more nanoseconds. Extensive air showers at a zenith angle of 70° with charged particles and Vavilov-Cherenkov radiation were also registered.     

Field Structure of the Cherenkov Radiation in a Waveguide

We study the field structure of the Vavilov-Cherenkov radiation in planar and cylindrical waveguides filled with a continuous dielectric medium or a uniaxial crystal. It is shown that the Vavilov-Cherenkov radiation has the form of wave packets propagating with the same phase and group velocities. Radiation from a system of charged-particle bunches is considered.     

Influence of an ambipolar field and target boundary blurring on transition radiation from fast electrons of laser plasma

It is shown that the blurring of the rear side of a thin laser target leads to a decrease in the intensity of higher harmonics in the spectrum of coherent transition radiation and that the scale of the boundary inhomogeneity can be estimated from the amplitude ratio of harmonics. Deceleration of the electron flow in an ambipolar electric field at the rear boundary of a target leads to a decrease in the intensity of lower harmonics in the spectrum of coherent transition radiation, and the strength of the ambipolar field can be estimated from the amplitude ratio of harmonics. A change in the permittivity of a dielectric laser target with frequency can lead to an increase in the intensity of some harmonics in the spectrum due to the Vavilov-Cherenkov mechanism.     

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.     

Vavilov-Cherenkov radiation from a model cascade developing near the lunar surface

The model problem of Vavilov-Cherenkov radiation emergence from lunar regolith into vacuum under LORD experimental conditions is considered. The boundary problem on radiation emergence into vacuum is solved numerically in the given field approximation (Kirchhoff approximation) from the cascade near the boundary (near-field region of the radiation source). The results are of great importance to interpret future experimental data.     

The SPHERE experiment: Baikal 2010

The SPHERE-2 detector was lifted above the snow-covered surface of Lake Baikal by a captive balloon several times in 2010. The Vavilov-Cherenkov radiation of extensive air showers was measured. Preliminary results from processing the data of the SPHERE-2 experiment at various altitudes of observation are presented.     

Emission accompanying superluminal motion of light

Conclusion We hope that we have succeeded in demonstrating the great scientific interest that attaches to superluminal motions of charges and to investigation of the radiation accompanying these motions. An extensive literature on superluminal motion is on hand even now. It deals, however, mainly with radiation in rectilinear motion, i.e., phenomena connected with the Vavilov-Cherenkov effect, the anomalous Doppler effect, ect. In the present note, on the other hand, principal attention is paid to the influence of the breakup of radiation of a single real source on the emission of several images visible by an immobile observer, which can take place for both uniform and nonuniform motion of the charges. From this viewpoint, new light is cast also on the anomalous Doppler effect. Breakup of one source into several images has been observed in all the considered examples.There is no doubt that the effect of several images can be observed in experiments, and possibly even used in practical electronics. From the viewpoint of observing the effect, most attention should be paid, in our opinion, to observation of the Vavilov-Cherenkov effect in a magnetic field (i.e., on a circular trajectory of a charge) in a medium. We note in this connection that to observe a doubling of a radiation source or vanishing of a pair of images there is no need to observe the entire circular trajectory—it suffices to observe only that part containing the points at which doubling of the source or vanishing of a pair of images takes place.Theoretical Division, Theoretical and Mathematical Physics, Lebedev Physics Institute. Translated from Preprint No. 194, Lebedev Physics Institute of the Academy of Sciences of the USSR, Moscow, 1989.     

The parametric Doppler effect upon oblique incidence of probe radiation

Transformation of frequency and intensity of probe radiation obliquely incident on a moving inhomogeneity induced by an intense laser radiation in a nonlinear medium is analyzed. The dependences of frequency and intensity of radiation reflected from the inhomogeneity have been found for a variant of frequency dispersion corresponding to collision-free plasma. These dependences possess singularities under conditions corresponding to the Vavilov-Cherenkov effect. The initially weak noise components of probe radiation increase in the reflected radiation up to a considerable value.     

Relativistic generalization of the Landau criterion as a new foundation of the Vavilov-Cherenkov radiation theory

The relativistic generalization of the Landau criterion is obtained for the determination of threshold conversion of medium elementary Bose-condensed excitation into Cherenkov's photon unbremsstrahlung radiation. In contraposition to classic Vavilov-Cherenkov radiation (VCR) theory, the new VCR theory admits the conditions for effective and direct VCR realization even for high-frequency transverse electromagnetic waves in isotropic plasma.     

Analysis of high multiplicity events

The experimental studies of the high multiplicity events in proton interactions are carried out on U-70 accelerator in Protvino. It is suggested that the collective phenomena can be discovered since the high density matter can be formed in this very region. The collective behavior of secondary particles can manifest in the Bose-Einstein condensation of pions, Vavilov-Cherenkov gluon radiation, excess of soft photon yield and other unique phenomena.     

超强脉冲激光辐照固体靶背表面的渡越辐射

 在超强脉冲激光与固体靶相互作用中,利用光学CCD相机和光学多道分析仪,分别在固体薄膜靶背表面法线方向测量了渡越辐射（TR）积分成像图案和光谱。测量结果显示：TR空间分布图案呈圆环状,而辐射区域有发散角和光强分布;TR光谱在800 nm附近出现尖峰,是激光的基频波,这一现象归因于超热电子束在输运的过程中产生的微束团而引起的相干渡越辐射;如果考虑超热电子的产生和加热机制,共振吸收和真空加热对超热电子都有贡献,其中占主导地位的加热机制则是共振吸收对电子的加热。     

Slow group velocity and Cherenkov radiation

We study theoretically the effect of ultraslow group velocities on the emission of Vavilov-Cherenkov radiation in a coherently driven medium. We show that in this case the aperture of the group cone on which the intensity of the radiation peaks is much smaller than that of the usual wave cone associated with the Cherenkov coherence condition. As a specific example, we consider a coherently driven ultracold atomic gas where such singular behavior may be observed.     

Superlight source of radiation with a waveguide used for bunching an electron beam

A scheme of a generator of electromagnetic-wave radiation is proposed in which a radiating region moves along a radiator with a velocity greater than the velocity of light in vacuum. The superlight motion of the generating region leads to the situation in which the resulting radiation has the properties of Vavilov-Cherenkov radiation. The electron beam of a superlight source is formed while the particles travel across a waveguide along which an electromagnetic wave propagates. The construction of the generator makes it possible to vary the velocity of the radiating region, the radiation pattern, and the radiation beamwidth. Calculations are performed that allow one to evaluate the parameters of the generator and the characteristics of radiation.     

The parametric doppler effect upon oblique radiation incidence in quartz glass

Frequency and reflection angle of probe radiation from a refractive-index inhomogeneity induced by an intense pumping pulse in quartz glass and moving with a relativistic velocity are calculated. Conditions under which the normal component of the wave vector of the reflected wave is directed to the opposite or to the same direction as the same component for the incident wave are determined. Comparison with the case of radiation reflection from a relativistic mirror in vacuum is performed. Conditions of the appearance of the Vavilov-Cherenkov radiation from a relativistic refractive-index inhomogeneity induced in the medium by an intense laser pulse are discussed.