Universal thermal radiation drag on neutral objects

We compute the force on a small neutral polarizable object moving at velocity v--> relative to a photon gas equilibrated at a temperature T. We find a drag force linear in v-->. Its physical basis is related to that in recent formulations of the dissipative component of the Casimir force, i.e., the change in photon momentum in emission and absorption between the moving body and the stationary thermal bath. We estimate the strength of this universal drag force for different dielectric response functions and comment on its relevance in various contexts, especially to radiation-matter coupling in the cosmos.     

电磁感应双光子光透明及共振吸收增强

研究了相干场控制下的电磁感应双光子光透明。讨论了外加相干场对双光子吸收特性的影响 ,分析了电磁感应双光子光透明及共振吸收增强的物理机制。应用密度矩阵方法推导出相干场作用下双光子吸收上能级粒子数的二阶近似表达式 ,同时利用微扰法在原子缀饰态表象中推导出双光子跃迁速率的解析表达式。并讨论了系统中多普勒效应的影响。     

Anomalous polarization dependence of the photon drag and optical rectification fields inn-type gallium phosphide

The photon drag and optical rectification response fromn-type gallium phosphide containing 2.4×10¹⁶ electrons cm^–3 has been studied using laser sources at 10.61 and 2.83m. By using different contact configurations, the existence of an additional electric field term in the propagation direction has been deduced. This field is shown to arise from the spatial derivatives of the photon drag and optical rectification field components caused by absorption of the radiation. The importance of this effect in detector design is considered.     

Photon-drag effect in a two-dimensional electron gas in high magnetic fields

We present the first measurements concerning the photon drag effect in a two-dimensional electron gas based on intersubband transitions in high magnetic fields. It is shown that the excitation mechanism of the drag voltage in a magnetic field differs obviously from the case of zero magnetic field. The longitudinal as well as the Hall drag voltage show strong oscillations around zero when the magnetic field is swept. Both consist of a B-symmetrical and an antisymmetrical part with the same periodicity in B as the magnetoresistanceR_xx. The drag voltage oscillations are strongly correlated to the relative position of Fermi energy and Landau levels and are independent of the photon energy in the range of usable laser lines.     

Electrodynamic response of a nanosphere placed in a magnetic field

Absorption of electromagnetic radiation by 2D electrons at the surface of a quantum sphere placed in a weak magnetic field is studied. It is shown that at low temperatures, the absorption curve exhibits four resonance peaks observed in the Faraday geometry (photon wave vector parallel to the magnetic field) and six peaks in the Voigt geometry (photon wave vector perpendicular to the magnetic field). In the particular case of the Voigt geometry, where the photon polarization vector is parallel to the magnetic field, the absorption curve exhibits only two resonance peaks. The shape, position, and intensity of the peaks are examined. It is shown that at temperatures close to zero, steps of two types appear in the absorption curve. One type of steps is associated with crossing of the μ-?ω level by the electron energy levels, while steps of the other type arise when electron energy levels cross the chemical potential μ.     

Multi-photon behaviors of shot noise in a quantum dot system under the perturbation of two microwave fields

We have investigated the shot noise affected by the perturbation of two microwave fields (MWFs) with frequencies ω₁ and ω₂, which can be classified as the commensurate and incommensurate external ac fields. The time-dependent current correlation function and the spectral density of shot noise have been obtained. They are very different compared with the single-field applied system in the nonlinear regime of the ac potentials. The different photon absorption and emission processes induce different kinds of noise spectral density. We have performed the numerical calculations for both commensurate balanced and unbalanced photon absorptions and emissions. The multi-photon procedure can be seen clearly from the resonance of shot noise. Different commensurate number q = ω₂/ω₁ contributes to different photon absorption and emission behaviors. It is found that the asymmetric configuration of shot noise is intimately associated with the commensurate number q. The differential conductance appears symmetric and asymmetric behaviors, and the channel blockade exhibits. The shot noise is large enough to surpass its saturated value for the unbalanced photon absorption case. The sensitive behaviors of Fano factor associated with different commensurate numbers and amplitudes of ac fields signify that the shot noise can be controlled by external MWFs significantly.     

拉曼散射在共振及近共振时的条件：广义短时间近似

研究了频率失谐时共振拉曼散射的动力学过程．当入射光子能量远离共振吸收能量时,时域内的失相使散射过程变快．这使得频率失谐如同照相机的快门功能,具有规律的散射持续时间,为普通的稳态测量提供了控制散射时间的有效工具．基于这个理论对两个多模式模型系统以及反式-1,3,5-己三烯和鸟嘌呤-胞嘧啶Watson-Crick碱基对分子的共振拉曼光谱进行了研究．除了这些特殊的物理效应,快散射机制可以简化光谱,同时使散射理论得到简化．当入射光子频率在共振区域时,拉曼光谱中会出现较强的多倍频成分;当入射光子频率与第一共振吸收频率之间的失谐量为振动能量时,在快散射过程中,这些多倍频成分逐渐消失．因此,利用入射光子与共振频域的失谐可以明显地简化拉曼光谱,从复杂光谱中去除多倍频和软模的影响,并且可以避免共振态的解离和荧光衰减引起的干扰．     

Resonant two-magnon Raman scattering and photoexcited States in two-dimensional mott insulators

We investigate the resonant two-magnon Raman scattering in two-dimensional (2D) Mott insulators by using a half-filled 2D Hubbard model in the strong coupling limit. By performing numerical diagonalization calculations for small clusters, we find that the Raman intensity is enhanced when the incoming photon energy is not near the optical absorption edge but well above it, being consistent with experimental data. The absence of resonance near the gap edge is associated with the presence of background spins, while photoexcited states for resonance are found to be characterized by the charge degree of freedom. The resonance mechanism is different from those proposed previously.     

Increase of refractive index induced by absorbing centres

An analytical expression of the complex permittivity is derived for absorbing centres featuring inhomogeneous absorption-line broadening. Such an expression gives the dispersion law of the real part of the permittivity when the imaginary part has a Gaussian lineshape. Our mathematical approach starts from an overlap integral of Lorentzian-type dielectric susceptibilities weighted by a Gaussian probability distribution of the resonance absorption energies. The analytical solution found is consistent with the Kramers–Kronig relation. We demonstrate that, like in the case of homogeneous absorption-line broadening, the refractive index increases at photon energies lower than the resonance absorption energy also for inhomogeneous absorption-line broadening; if the absorbing centres emit Stokes-shifted radiation, such an increase can be exploited for passive and active waveguiding applications. An example is reported regarding active waveguides based on colour centres in a lithium fluoride crystal.     

Collapse and revivals of the photon field in a Landau-Zener process

We consider the evolution of a two-level system coupled to a photon field initially in a coherent state, as the energy of the two-level system is linearly varied through resonance with the photon field. At a fixed time after the resonance, the amplitude of the photon field is found to show a collapse and subsequent revivals as a function of rate of energy variation. Including decay of the photon field, we find that the observation of such collapse and revivals is near the technological limit of current cavity QED experiments but should be achievable.     

Resonant Photon Drag of Dipolar Excitons

The theory of the photon drag of dipolar excitons in double-quantum-well nanostructures is presented. It is shown that the exciton-drag flux density features a resonant behavior if the photon frequency is close to some transition frequency in the discrete exciton spectrum. When the structure is irradiated with polarized light, the resonant enhancement of the drag current occurs when the photon energy coincides with the energy of an excited level of the exciton internal motion and the components of the angular momentum of internal motion in the initial and final states differ by one. The proposed effect can be used to control exciton transport in nanostructures based on a two-dimensional exciton gas.     

Odderon and photon exchange in electroproduction of pseudoscalar mesons

We investigate the reaction where PS denotes a pseudoscalar meson , , , or and X either a proton or resonance or continuum state into which the proton can go by diffractive excitation. At high energies photon and odderon exchange contribute to the reaction. The photon exchange contribution is evaluated exactly using data for the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark structure as suggested by the small odderon amplitude in pp and forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic PS production cross section. Observation of our reaction at HERA would establish the soft odderon as an exchange object on an equal footing with the soft pomeron and would give us valuable insight into both the nucleon structure and the mechanism of high energy diffractive scattering. Received: 2 February 1999 / Revised version: 22 March 1999 / Published online: 28 May 1999     

Photoexcitation of a volume plasmon in C60 ions

Neutral C60 is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements for C+60, C2+60, and C3+60 ions in the 17-75 eV energy range show an additional resonance near 40 eV. Time-dependent density functional calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry.     

Features of the electron-photon drag effect in a spiral ribbon in the external magnetic field

The features of the photon drag effect in a spiral two-dimensional ribbon, which are associated with an asymmetric electron energy spectrum in a longitudinal magnetic field, have been studied theoretically. The effect of the anisotropic transfer of the photon momentum to the electron system in a spectral dependence of the photon drag current density has been revealed.     

Drag effect of one-dimensional electrons upon photoionization of D<Superscript>(−)</Superscript> centers in a longitudinal magnetic field

A theory is elaborated for the impurity photon drag effect in a semiconductor quantum wire exposed to a longitudinal magnetic field B directed along the axis of the quantum wire. The phonon drag effect is associated with the transfer of the longitudinal photon momentum to localized electrons in optical transitions from D^(?) states to hybrid-quantized states of the quantum wire, which is described by a confinement parabolic potential. An analytical expression for the drag current density is derived within the model of a zero-range potential in the effective mass approximation, and the spectral dependence of the drag current density is examined at different magnitudes of B and parameters of the quantum wire upon electron scattering by a system of impurities with short-range potentials. It is established that the spectral dependence of the drag current density exhibits a Zeeman doublet with a clear beak-shaped peak due to optical transitions of electrons from D^(?) states to states with the magnetic quantum number m=1. The possibility of using the photon drag effect in a longitudinal magnetic field for the development of laser radiation detectors is analyzed.     

Plasma resonance absorption in interfacial photoemission from very thin silver films on Cu(111)

Very thin silver films deposited on a Cu(111) substrate were studied with the photoemission-into-electrolyte technique. The optical resonance absorption at the silver bulk plasma frequency was observed for films thicker than two monolayers. The correlation between optical absorption and photoemission intensities depends in a complicated fashion on the photon energy as well as the film thickness.     

Exciton-polariton state in nanocrystalline SiC films

We studied the features of optical absorption in the films of nanocrystalline SiC (nc-SiC) obtained on the sapphire substrates by the method of direct ion deposition. The optical absorption spectra of the films with a thickness less than ~500 nm contain a maximum which position and intensity depend on the structure and thickness of the nc-SiC films. The most intense peak at 2.36 eV is observed in the nc-SiC film with predominant 3C-SiC polytype structure and a thickness of 392 nm. Proposed is a resonance absorption model based on excitation of exciton polaritons in a microcavity. In the latter, under the conditions of resonance, there occurs strong interaction between photon modes of light with λ_ph=521 nm and exciton of the 3С polytype with an excitation energy of 2.36 eV that results in the formation of polariton. A mismatch of the frequencies of photon modes of the cavity and exciton explains the dependence of the maximum of the optical absorption on the film thickness.     

Spin photocurrents and the circular photon drag effect in (110)-grown quantum well structures

The study of spin photocurrents in (110)-grown quantum well structures is reported. The investigated effects comprise the circular photogalvanic effect and so far not observed circular photon drag effect. The experimental data can be described by an analytical expression derived from a phenomenological theory. A microscopic model of the circular photon drag effect is developed demonstrating that the generated current has a spin dependent origin. The text was submitted by the authors in English.     

苝四甲酸二酐薄膜电子结构的同步辐射共振光电子能谱研究

利用基于同步辐射的近边X射线吸收精细结构谱(NEXAFS)和共振光电子谱(RPES)研究了苝四甲酸二酐分子(PTCDA)薄膜的电子结构.碳K边NEXAFS谱中能量小于290 eV的四个峰对应于PTCDA分子不同化学环境碳原子1s电子到未占据分子轨道的共振跃迁.RPES谱中观察到共振光电子发射和共振俄歇电子发射导致的共振峰结构,以及二次谐波激发的碳1s信号.根据电子动能对入射光能量的依赖性分别对三类峰结构进行了归属.同时,发现PTCDA分子轨道共振光电子峰的强度具有光子能量依赖性.这种能量选择性共振增强效应是由于PTCDA分子轨道空间分布差异导致的.共振俄歇峰主要源于高结合能(4.1 eV)分子轨道能级电子参与的退激发过程.明确RPES实验谱图中各个峰结构的起源有助于准确利用基于RPES的芯能级空穴时钟谱技术定量估算有机分子/电极异质界面处电子从分子未占据轨道到电极导带的超快转移时间.     

Transverse photon drag detection of FIR radiation by free carriers in antimony thin films

Fast and sensitive detection of far-infrared radiation pulses have been observed in large-area Sb thin films by means of transverse photon drag of free carriers. The direct sensitivity was greater than 1 V/MW, about 10–30 times the normal sensitivity of Ge photon drag at 10 μm wavelength. These films are ideal for power detection of fast large-area FIR pulsed emissions.