Waves in resonant random media

Abstract

Electromagnetic properties of resonant inhomogeneous media are investigated. A new type of transverse electromagnetic wave arising due to the effective spatial dispersion is studied. It is shown that scattering on the fluctuations of the resonant frequency of the medium shifts the Cherenkov threshold and reduces the intensity of the Cherenkov radiation.     

Resonant diffusive radiation in random multilayered systems

We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. The resonant condition can be satisfied for the wavelength region representing visible light as well as soft X rays. The intensity of diffusive soft X rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at a photon energy of 99.4 eV, the intensity of resonant diffusive radiation (RDR) generated by 5-MeV electrons passing a Be/Si multilayer exceeds the intensity of Cherenkov radiation by a factor of ≈60 for electrons with the same energy passing a Si foil. For a photon energy of 453 eV and 13 MeV, electrons passing a Be/Ti multilayer generate RDR exceeding the Cherenkov radiation generated by electrons passing Ti foils by a factor ≈130.     

Quantization of the motion and Cherenkov structure of a Josephson vortex

A generalization of the Sakai-Tateno-Pedersen model is proposed. This model is used to establish the existence of a discrete eigenvalue spectrum of the free-motion velocities of a Josephson vortex, or π kink, produced by the Cherenkov structure of extraordinary vortex-trapped Swihart waves having the spectrum (3.9). The dependence of the current across the Josephson junction on the vortex velocity was obtained, and, at comparatively high velocities, this was characterized by equidistant dips attributable to the Cherenkov resonant interaction of the vortex with Swihart waves.     

Frequency-doubled vortex beam emitter based on nonlinear Cherenkov radiation

In this work, we propose a new scheme to generate frequency-doubled vortex beams from a radially poled Li Nb O3 micro-ring resonator based on nonlinear Cherenkov radiation. The near-infrared fundamental wave is resonant in the micro-ring, while the second harmonic is emitted from the resonator along the Cherenkov phase-matching direction. The topological charge of the emitted second-harmonic vortex beam is determined by both the azimuthal order of the whispering galley modes and the number of nonlinear grating elements. The field distribution and the conversion efficiency of the emitted vortex beam are investigated.     

Beam-plasma interaction as affected by an “axial” inhomogeneity

The effect of axial (with respect to the direction of beam propagation) inhomogeneity on the process of slow surface wave (SW) resonant excitation by a relativistic monoenergetic beam of charged particles is investigated. The allowance for the inhomogeneity is demonstrated to change the natural frequencies of excited SW and thus violate the Cherenkov SW-beam-resonance. A dispersion equation and growth rates of the excited waves are obtained, taking into account the density inhomogeneity.     

“Inversionless” stimulated emission of radiation by nonequilibrium ensembles of classical oscillators

We find classical analogs of quantum systems capable of stimulated emission of radiation in the absence of inversion. We show that cyclotron parametric instability in low-frequency modulation of the distribution function of resonant particles can amplify a bichromatic high-frequency field when amplification of each spectral component separately is impossible. We point to similar modes for a Cherenkov resonance and a model system with lumped parameters. Finally, we suggest using this effect for converting microwave radiation to a higher frequency. Zh. éksp. Teor. Fiz. 112, 1176–1196 (October 1997)     

Cherenkov radiation waves in inhomogeneous dusty plasma

A kinetic theory is employed to study Cherenkov wave in an inhomogeneous dusty plasma. Two different frequency regimes are considered incorporating the plasma species temperatures. The dispersion relation for one-dimensional Cherenkov wave is derived and analyzed. The plasma species temperatures, their cyclotron frequencies, and the plasma density inhomogeneity effect the growth/damping of Cherenkov waves. It is shown that the plasma inhomogeneity contributes to damping of Cherenkov waves.     

Spatial distribution of Cherenkov light from cascade showers in water

The spatial distribution of the Cherenkov light generated by cascade showers is analyzed using the NEVOD Cherenkov water detector. The dependence of the Cherenkov light intensity on the depth of shower development at various distances from the shower axis is investigated for the first time. The experimental data are compared with the Cherenkov light distributions predicted by various models for the scattering of cascade particles.     

Stimulated Cherenkov emission in gas dynamics

A linear theory is developed for stimulated Cherenkov emission from planar and cylindrical gas flows in gaseous environments. An analogy is demonstrated between Cherenkov emission in gas dynamics and stimulated Cherenkov electromagnetic emission from a charged particle beam in a medium.     

Cherenkov Radiation in Moving Medium

Cherenkov radiation in uniformly moving homogeneous isotropic medium without dispersion is studied. Formula for the spectrum of Cherenkov radiation of fermion was derived for the case when the speed of the medium is less than the speed of light in this medium at rest. The properties of Cherenkov spectrum are investigated.     

铁电晶体畴壁增强非线性性质的研究

通过研究畴壁切伦科夫倍频,发现畴壁存在巨大增强的非线性系数.由此造成的畴壁“定域性”使其可以对非线性极化波产生相速度调制,进而影响切伦科夫倍频.提出并证实了极限切伦科夫倍频的存在,并分析了它和准相位匹配倍频产生的区别.     

Investigation of coherent Vavilov-Cherenkov radiation in the millimeter wavelength range generated in PTFE and paraffin target

In this paper, we present an experimental observation of coherent Cherenkov radiation in the millimeter wavelength range. Coherent Cherenkov radiation is generated by a 6.1-MeV bunched electron beam passing by dielectric targets (PTFE and paraffin). The characteristics of Cherenkov and diffraction radiation measured under the same conditions are compared. The experiment is carried out with the electron beam of the microtron at Tomsk Polytechnic University.     

Electromagnetic properties of open and closed overmoded slow-waveresonators for interaction with relativistic electron beams

Specific slow wave structures are needed in order to produce coherent Cherenkov radiation in overmoded relativistic generators. The electromagnetic characteristics of such slow wave, resonant, finite length structures commonly used in relativistic backward wave oscillators have been studied both experimentally and theoretically. In experiments, perturbation techniques were used to study both the fundamental and higher order symmetric transverse magnetic (TM) modes. Finite length effects lead to end reflections and quantization of the wave number. The effects of end reflections in open slow wave structures were found from the spectral broadening of the discrete resonances of the different axial modes. The measured axial and radial field distributions are in excellent agreement with the results of a 2-D code developed for the calculation of the fields in these structures     

Features of transition and Cherenkov radiations and the correlation between them

It is shown that transition radiation arising at the boundary of two media is being emitted as a Cherenkov one, if the phase velocity of transition radiation waves in the medium of transition radiation propagation becomes equal to the velocity of the moving radiating particle (the necessary condition for the Cherenkov radiation). The proof of this statement is based on the analysis of the transition radiation formation zone, which may become large enough and provide interference between the field of transition radiation and the own Coulomb field of the moving particle, in case when the Cherenkov radiation condition is fulfilled. As a result, the transition radiation field transforms into the Cherenkov field. The problem is considered for cases of both a waveguide and free space.     

水下Co-60源切伦科夫辐射的蒙卡模拟

随着核应用领域的不断拓宽,放射源丢失事故发生的概率也随之增加。机载伽马谱仪可有效搜寻地面放射源,然而对于放射源丢失于水域的情况,由于伽马射线经由水层屏蔽后可探测性降低,故利用放射源在水中产生的切伦科夫辐射对其进行搜寻显得十分重要。采用MCNP与Geant4相结合的方法,以及在Geant4程序中采用接续计算技巧,对Co-60源在水中的切伦科夫光产生以及传输进行了计算,计算表明,切伦科夫光经水中传播后,主要波段在300~600 nm,强度呈由边缘到中心渐强的特征分布,分布范围大致与放射源在水中的深度一致,在水中传输300 m后其光通量约为100 cm-2,可利用光谱特征和强度分布特征对其进行测量。     

On the polarization characteristics of Cherenkov radiation from a dielectric screen

The Cherenkov effect is a well-known phenomenon and its properties are widely used in many fields of physics. However, some features of the polarization characteristics of Cherenkov radiation that appears when charged particles pass near azimuthally asymmetric, finite dielectric targets are still poorly studied. This problem is solved in this work. The polarization characteristics of Cherenkov radiation in the case of a rectangular dielectric screen are analyzed using the Stokes approach. Owing to the azimuthal asymmetry of the target, radiation acquires an elliptic polarization whose rotation direction and inclination angle depend both on the direction of radiation propagation and on the dielectric properties of a substance. The results demonstrate that the Cherenkov effect can be used to create sources of elliptically polarized radiation with the controlled direction of polarization rotation.     

Nonlinear optical terahertz wave sources

We developed a Cherenkov phase-matching method for monochromatic THz-wave generation using the DFG, process with a lithium niobate crystal, which resulted in both high conversion efficiency and wide tunability. Although THz-wave generation by Cherenkov phase matching has been demonstrated using femtosecond pumping pulses, producing very high peak power, these THz-wave sources are not monochromatic. Our method generates monochromatic and tunable THz, waves using a nanosecond pulsed laser source. We also show that Cherenkov radiation with waveguide structure is an effective strategy for achieving extremely wide tunable THz-wave source. We fabricated MgO-doped lithium niobate slab waveguide and demonstrated difference frequency generation of THz-wave generation with Cherenkov phase matching. Extremely frequency-widened THz-wave generation, from 0.1 to 7 THz was observed.     

宇宙线μ子的大气契仑柯夫光像

给出理想条件下聚光镜焦平面上单个μ子大气契仑柯夫光像的理论结果．简要地介绍在标定第二代大气契仑柯夫光成像望远镜中的应用．