Generation of subnanosecond microwave pulses based on the Cherenkov superradiance effect

Experimentally observed Cherenkov superradiance produced by a subnanosecond electron bunch traveling through a partially filled waveguide is reported. 400-ps microwave pulses with a peak power of 2 MW are obtained. The experimental results are in good agreement with the theoretical analysis and numerical simulations performed with the help of the PIC code KARAT.     

A tunable frequency-decuple optoelectronic oscillator based on frequency comb and stimulated Brillouin scattering

An optically tunable frequency-decuple optoelectronic oscillator based on optical frequency comb (OFC) and stimulated Brillouin scattering has been proposed and theoretically analyzed. In the proposed structure, the OFC is generated using a cascaded Mach–Zehnder modulator and a dual-parallel Mach–Zehnder modulator (DPMZM), and multi-pump lights could be obtained instead of one pump. A quintuple Brillouin frequency shift oscillation signal generated by using Brillouin gain-loss compensation principle and carrier phase-shifted double sideband modulation is realized by using the DPMZM to double the oscillation frequency. As a consequence, a decuple frequency shift microwave signal is achieved. Profit from the wavelength-dependent nature of Brillouin frequency shift, a frequency-decuple signal at 10 \(f_{b}\) which could be tunable from 87.9750 to 94.4750 GHz by simply tuning the wavelength of the tunable laser source is obtained in theory.     

一种基于串联谐振腔的高性能光电振荡器

提出了一种利用串联谐振腔来抑制光电振荡器边模的方案. 此方案中, 在传统光电振荡器结构中加入无源微波谐振腔结构来提高滤波器的Q值. 分析了该结构的基本原理, 并与传统光电振荡器结构进行对比, 此结构能有效提高边模抑制比. 实验中产生了10 GHz的微波信号, 所测得的边模抑制比达72 dB, 单边带相位噪声为-122 dBc/Hz@10 kHz. 同时, 利用锁相技术, 振荡频率的稳定性得到了很大的改善, 在3 h内漂移小于± 4 Hz. 该方案无需增加有源器件, 保留了传统光电振荡器低相位噪声的优势, 又有效抑制了边模, 为光电振荡器的应用提供了一种新的方法.     

An extended interaction oscillator based on a complex resonatorstructure

We report experimental investigation of a novel scheme for efficient interaction between a linear electron beam and an electromagnetic wave in a complex extended interaction structure. The structure of interest consists of a high R/Q, five-gap, coupled-cavity resonator that incorporates a coaxial section of a quarter plasma wavelength placed between the first and second cavities. In the coaxial section, beam and wave propagate in separate channels. The first cavity, strongly coupled to the other cavities through the wave channel of the coaxial section, serves as a buncher cavity. An inner channel running through the center conductor of the coaxial section provides a cutoff drift space for ballistic bunching of electrons, an effect that is shown to significantly enhance the interaction efficiency. Oscillation power of 2.2 kW at 16.6 GHz was demonstrated with an interaction efficiency of 30%. The total efficiency was further increased to 41% by incorporation of a two-stage depressed collector     

An Experimental Study on Cyclotron–Cherenkov Radiation

We searched numerically dielectric-loaded cylindrical waveguide configurations with an injected electron beam in which the growth rate of the cyclotron-Cherenkov instability surpassed that of the Cherenkov instability, and found such a configuration. This configuration consists of a metallic core and an outer metallic cylinder with a dielectric liner on the inner surface. In order to investigate experimentally radiation due to the cyclotron-Cherenkov instability, we designed and assembled an experimental device using the computational results. We studied beam propagation in the dielectric-loaded coaxial waveguide and microwave radiation due to the cyclotron-Cherenkov instability and the Cherenkov instability.     

Non-relativistic quantum theory of stimulated Cherenkov radiation and Compton scattering in plasma

The stimulated processes in electron plasma, i.e., Cherenkov radiation by a nonrelativistic electron beam of longitudinal oscillations and Compton scattering of a transverse electromagnetic wave in plasma with quantum mode excitation (de Broglie wave), are considered in the three-wave approximation. The possibility of the occurrence of quantum oscillations is discussed.     

平板波导中切伦科夫型级联二阶非线性效应的理论分析

用解析的方法详细讨论了平板波导中的切伦科夫型级联二阶非线性效应引起的基波非线性相位移动和基波功率的变化。结果表明，通过选择合适的反转周期，可以得到相当大的基波非线性相位移动（大于π）。由于切伦科夫型非线性器件结构比准相位匹配器件具有更大的容差，并且基波和谐波自然分离，切伦科夫型级联二阶非线性效应引起的基波非线性相位移动在全光开关器件中有着重要的应用。     

An interferometer based on the Talbot effect

The moiré effect is very sensitive in detecting small differences between two similar gratings. These differences might be caused by an object with phase gradient placed between the two gratings. The performance of such an instrument can be understood in terms of the “Talbot effect” (also called “Fourier imaging” or “self-imaging”). Slight modifications provide shearing interferences and the second derivative of the object.     

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.     

Gravitational Cherenkov losses in theories based on modified Newtonian dynamics

Survival of high-energy cosmic rays (HECRs) against gravitational Cherenkov losses is shown not to cast strong constraints on modified Newtonian dynamics (MOND) theories that are compatible with general relativity (GR): theories that coincide with GR for accelerations ?a(0) (a(0) is the MOND constant). The energy-loss rate, E, is many orders smaller than those derived in the literature for theories with no extra scale. Modification to GR, which underlies E, enters only beyond the MOND radius of the particle: r(M)=(Gp/ca(0))(1/2). The spectral cutoff, entering E quadratically, is thus r(M)(-1), not k(dB)=p/?. Thus, E is smaller than published rates, which use k(dB), by a factor ～(r(M)k(dB))(2)≈10(39)(cp/3×10(11) Gev)(3). Losses are important only beyond D(loss)≈q?(M), where q is a dimensionless factor, and ?(M)=c(2)/a(0) is the MOND length, which is ≈2π times the Hubble distance.     

Single-particle Cherenkov effect in a bounded spatial region

The problem of the development of a beam instability in a bounded spatial region due to the single-particle Cherenkov effect is studied in the linear approximation. The threshold conditions for the onset of the convective and absolute instabilities of different longitudinal modes and their growth rates are determined with allowance for reflections from the boundaries of the system.     

X-ray diffraction radiation in conditions of Cherenkov effect

X-ray diffraction radiation from ultra-relativistic electrons moving near an absorbing target is considered. The emission yield is found to increase significantly in conditions of Cherenkov effect.     

An analysis of the autodyne effect of a radio-pulse oscillator with frequency modulation

The results of investigations of an autodyne oscillator with concurrent pulse-and frequency modulation are presented, with the oscillator being affected by its own reflected radiation. The main relations for the analysis of the autodyne response with respect to the time delay of the reflected radiation are presented for the case of an arbitrary frequency modulation law. Special features of self-oscillations of such autodynes are addressed, which permit improvement of the characteristics and extension of the functional capabilities of autodyne systems in SRR applications. The analytical results are verified using the experimental prototypes of the autodyne sensors based on the oscillators employing the mm-range Gunn diodes operating on well-known principles. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 80–88, July, 2008.     

Cherenkov effect as a probe of photonic nanostructures

Electron energy-loss spectroscopy (EELS) is shown to be an excellent source of information both on photonic crystal bands and on radiation modes of complex nanostructures. Good agreement is reported between measurements and parameter-free calculations of EELS in porous alumina films, where Cherenkov radiation is scattered by the pores to yield a strong 8.3-eV (7-eV) feature for 120-keV (200-keV) electrons. The latter is related to the bands of two-dimensional photonic crystals formed by air cylinders in an alumina matrix with similar near-range ordering. Finally, the band structure is proved to be directly mapped by angle-resolved EELS.     

Vacuum Cherenkov effect in logarithmic nonlinear quantum theory

We describe the radiation phenomena which can take place in the physical vacuum such as Cherenkov-type shock waves. Their macroscopical characteristics - cone angle, flash duration, radiation yield and spectral distribution - are computed. It turns out that the radiation yield is proportional to the square of the proper energy scale of the vacuum which serves also as the vacuum instability threshold and the natural ultraviolet cutoff. While the analysis is mainly based on the theory engaging the logarithmic nonlinear quantum wave equation, some of the obtained results must be valid for any Lorentz-invariance violating theory describing the vacuum by (effectively) continuous medium in the long-wavelength approximation.     

The influence of stimulated temperature-dependent emission cross section on intracavity optical parametric oscillator

In this paper, the influence of temperature on the intracavity optical parametric oscillator(IOPO) is investigated by using the stimulated temperature-dependent emission cross section of laser crystal. The rate equations under plane wave approximation have been used for simulation of signal output pulse. Results show that the signal output pulse width is decreased by increasing the laser crystal temperature. Also, the signal output energy is increased by the increasing of the laser crystal temperature. The simulation results for IOPO based on Nd:YAG and Nd:YVO_4, show that the signal pulse energies are increased by 3.2 and 5.6 times respectively when the laser crystal temperature increased from 15℃ to 300℃. The presented model indicates that the temperature sensitivity of Nd:YVO_4-based IOPOs is more than that of Nd:YAG-based IOPOs which is expected from a physical point of view.     

The effect of singular potentials on the harmonic oscillator

We address the problem of a quantum particle moving under interactions presenting singularities. The self-adjoint extension approach is used to guarantee that the Hamiltonian is self-adjoint and to fix the choice of boundary conditions. We specifically look at the harmonic oscillator added of either a δ-function potential or a Coulomb potential (which is singular at the origin). The results are applied to Landau levels in the presence of a topological defect, the Calogero model and to the quantum motion on the noncommutative plane.     

准相位匹配PPMgLN光参量振荡技术

 理论上分析了PPMgLN光参量振荡波长调谐特性,计算了泵浦阈值和转换效率。准相位匹配情况下,周期调谐是获得中红外波长调谐有效方法之一。采用高斯光束泵浦,当泵浦功率密度超过阈值泵浦功率密度约6.5倍时,可以获得最高转换效率,约71%。采用1 064 nm激光泵浦多周期PPMgLN晶体,实验上获得了波长调谐范围2.7~4.8 mm,当泵浦功率为8 W时,在波长3.7 mm处激光输出功率超过1.6 W,斜效率超过20%,相应的转换效率约为69%,与理论分析基本一致。     

基于OTRA的正弦波振荡器的设计

基于OTRA,MOS非平衡电阻(MRC)及电容,给出了OTRA-MOSFET-C无损积分器及有损积分器,该积分器能减小寄生电容的影响,由此构造了理想正交正弦振荡器,最后给出了OTRA实用正交振荡器,该振荡器不仅能同时得到2个相位互差90°的正弦波,而且容易起振,振荡频率、输出幅度可电控调谐,且互不影响,输出频率稳定.