Photon acceleration in vacuum

A new process associated with the nonlinear optical properties of the electromagnetic vacuum, as predicted by quantum electrodynamics, is described. This can be called photon acceleration in vacuum, and corresponds to the frequency shift that takes place when a given test photon interacts with an intense beam of background radiation.     

激光尾波场中光子加速研究

在SILEX-Ⅰ激光装置上,测量了超短超强激光脉冲与稀薄等离子体相互作用之后的透射谱. 实验中发现,激光尾波场产生的密度扰动导致等离子体折射率随时间空间不断变化,导致光子的加速/减速. 透射谱上主要表现为激光频率谱峰的劈裂和随密度变化的展宽,没有发现与前向受激拉曼散射或自调制不稳定性相联系的边频波. 同时,利用LPIC++无碰撞粒子模拟程序模拟了超短超强激光与稀薄等离子体相互作用后的透射谱,模拟结果也发现了明显的光子加速过程. 关键词： 超短超强激光脉冲 透射谱 光子加速/减速     

Photon bubbles and ion acceleration in a plasma dominated by the radiation pressure of an electromagnetic pulse

The stability of a thin plasma foil accelerated by the radiation pressure of a high intensity electromagnetic (e.m.) pulse is investigated analytically and with particle in cell numerical simulations. It is shown that the onset of a Rayleigh-Taylor-like instability can lead to transverse bunching of the foil and to broadening of the energy spectrum of fast ions. The use of a properly tailored e.m. pulse with a sharp intensity rise can stabilize the foil acceleration.     

Suppression of superluminous precursors in high-power backward Raman amplifiers

The very promising scheme for producing ultrapowerful laser pulses through Raman backscattering of pump lasers in plasmas can be jeopardized by superluminous precursors. Growing from the leading part of the Raman pumped seed pulse, these precursors can disturb the plasma and the pump ahead of the pumped pulse. These ruinous effects, however, might be averted by a detuning, large enough to suppress the precursors, yet small enough to allow the desired backscatter effect.     

Conversion of electrostatic to electromagnetic waves by superluminous ionization fronts

The conversion of static electric fields to electromagnetic radiation by the incidence of a superluminous ionization front on plasma is investigated. For extremely superluminous fronts, the radiation is close to the plasma frequency and is converted with efficiency of order unity. A proof-of-principle experiment was conducted using semiconductor plasma containing an alternately charged capacitor array. The process has important implications in astrophysical plasmas, such as supernova emission, and to laboratory development of compact, coherent, tunable radiation sources in the THz range.     

Photon channelling in foams

Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling only occurs in a finite range of ɛ.     

Photon clocks

The original construction of a photon clock by von Laue is noted. Several intrinsic difficulties inhibitory to the free use of such clocks are described.     

Photon recyclers

We present a radical approach for improving the efficiency of optically pumped NMMW lasers in which the Manley-Rowe limit is transcended by recycling pump photons. The resulting new class of lasers, called photon recyclers, can be described as heat engines in which heat is converted into coherent NMMW radiation using pump photons as a catalyst. Practical implementation of the proposed schemes by combining features of optically pumped NMMW lasers and gas dynamic expansion is discussed. Such systems may yield high power c.w. NMMW output.Work supported by U.S. Army Research Office, Durham, NC.     

Photon Stars

We discuss numerical solutions of Einstein's field equation describing static, spherically symmetric conglomerations of a photon gas. These equations imply a back reaction of the metric on the energy density of the photon gas according to Tolman's equation. The 3–fold of solutions corresponds to a class of physically different solutions which is parameterized by only two quantities, i.e. mass and surface temperature. The energy density is typically concentrated on a shell because the center contains a repelling singularity, which can, however, not be reached by timelike geodesics and only by radial null geodesics. The physical relevance of these solutions is completely open, although their existence may raise some doubts w.r.t. the stability of black holes.     

Photon Statistics of Single-Photon Quantum States in Real Single Photon Detection

Single photon detection (SPD) with high quantum efficiency has been widely used for measurement of different quantum states with different photon distributions.Based on the direct single SPD and double-SPD of HBT configuration, we discuss the effect of a real SPD on the photon statistics measurement and it shows that the measured photon distributions for different quantum states are corrected in different forms.The results are confirmed by experiment with the strongly attenuated coherent light and thermal light.This system can be used to characterize the photon statistics of the fluorescence light from single atom or single molecular.     

Particle acceleration mechanisms in the auroral acceleration region

Particle acceleration by double layers is compared with other possible mechanisms of particle acceleration in the auroral acceleration region. Emphasis is on a recent suggestion that electrostatic wave turbulence is the only tenable explanation for particle acceleration in the auroral acceleration region     

Structure of the axial intensity minima in the Fresnel diffraction on a circular opening and superluminous effects

The “classical” problem of plane-wave diffraction by a circular opening is inspected with one particular interest to check the existence of axial zeroes of amplitude, which can produce a specific type of phase singularities. We investigate the problem using paraxial and nonparaxial solutions of scalar wave equation based on Hankel transform. The main result of investigation is the detection of the absence of any exact amplitude zeroes in the Fresnel diffraction field. Instead, sharp phase variations localized at the regions of axial amplitude minima with longitudinal and transversal dimensions of the order of one wavelength are revealed. These phase variations influence on the phase velocity, which drops up to c/2 in the point of axial amplitude minimum. Also, superluminous effects of wavefront propagation are discussed.     

波荡器辐射的空间分布与接受孔的选择

对波荡器谐波辐射的空间分布作了分析，并对上海同步辐射装置（SSRF）的波荡器U3．65辐射强度的空间分布进行数值模拟研究，在此基础上，探讨了波荡器辐射的接受孔尺寸选择，并模拟计算了SSRF U3．65的孔传输通量和功率。     

Two-Photon Processes and Photon Structure

In this article aspects of photon-photon physics related to the structure of real and virtual photons are reviewed. A recalculation of the virtual photon-photon box is performed and some discrepancies in the literature are clarified. A useful compilation of various relevant limits derived from the most general expressions is provided. Furthermore, structure functions of spin-averaged, transverse, and longitudinal virtual target photons are defined and discussed. Finally, the factorization of two-photon processes in the Bjorken limit is demonstrated to hold also for the case of virtual target photons.