Near QED regime of laser interaction with overdense plasmas

Interaction of laser plulses with intensities up to 10²⁵?W/cm² with overdense plasma targets is investigated via three-dimensional particle-in-cell simulations. At these intensities, radiation of electrons in the laser field becomes important. Electrons transfer a significant fraction of their energy to γ-photons and obtain strong feedbacks due to radiation reaction (RR) force. The RR effect on the distribution of laser energies among three main species: electrons, ions and photons is studied. The RR and electron-positron pair creation are implemented by a QED model. As the laser intensity inreases, the ratio of laser energy coupled to electrons drops while the one for γ-photons reaches up to 35%. Two distinctive plasma density regimes of the high-density carbon target and low-density solid hydrogen target are identified from the laser energy partitions and angular distributions of photons. The power-laws of absorption efficiency versus laser intensity and the transition of photon divergence are revealed. These show enhanced generation of γ-photon beams with improved collimation in the relativistically transparent regime. A new effect of transverse trapping of electrons inside the laser field caused by the RR force is observed: electrons can be unexpectedly confined by the intense laser field when the RR force is comparable to the Lorentz force. Finally, the RR effect and different regions of photon emission in laser-foil interactions are clarified.     

Nonlinear interaction of ultraintense laser pulse with relativistic thin plasma foil in the radiation pressure-dominant regime

We present a study of the effect of laser pulse temporal profile on the energy /momentum acquired by the ions as a result of the ultraintense laser pulse focussed on a thin plasma layer in the radiation pressure-dominant (RPD) regime. In the RPD regime, the plasma foil is pushed by ultraintense laser pulse when the radiation cannot propagate through the foil, while the electron and ion layers move together. The nonlinear character of laser–matter interaction is exhibited in the relativistic frequency shift, and also change in the wave amplitude as the EM wave gets reflected by the relativistically moving thin dense plasma layer. Relativistic effects in a high-energy plasma provide matching conditions that make it possible to exchange very effectively ordered kinetic energy and momentum between the EM fields and the plasma. When matter moves at relativistic velocities, the efficiency of the energy transfer from the radiation to thin plasma foil is more than 30% and in ultrarelativistic case it approaches one. The momentum /energy transfer to the ions is found to depend on the temporal profile of the laser pulse. Our numerical results show that for the same laser and plasma parameters, a Lorentzian pulse can accelerate ions upto 0.2 GeV within 10 fs which is 1.5 times larger than that a Gaussian pulse can.     

Correlation of the energies of photons emitted in cascade transitions

New details of a well-known physical process—cascade transition—have been considered. The wave function of a system of two photons emitted in a cascade transition in the absence of a shift of the phase of the intermediate state was studied. The joint energy distribution density for two such photons is obtained by numerical calculation, and a correlation between their energies at certain probabilities of radiative transitions is ascertained. This phenomenon can be used to diagnose the plasma density.     

双光子吸收材料二苯乙烯衍生物的合成及光谱性质

设计、合成并用红外光谱、1H NMR、元素分析表征了三种用于双光子吸收材料的二苯乙烯衍生物,4,4′-双(二苯氨基-反式-苯乙烯基)联苯(BPSBP),4,4′-双(二乙氨基-反式-苯乙烯基)联苯(BESBP)和4,4′-双(9-咔唑基-反式-苯乙烯基)联苯(BCSBP)。实验结果表明三者最强的单光子吸收出现在350～400 nm之间,且单光子吸收和荧光光谱中表现出明显的溶剂化显色效应,揭示了分子内对称电荷转移的本质,双光子荧光光谱则揭示了单光子和双光子吸收具有相同的发射机理。利用双光子上转换荧光法测试发现,三种双光子吸收材料在800 nm飞秒激光的激发下具有较大的吸收截面,分别为892,617和483 GM,这表明在双光子领域有潜在的应用价值。     

Confined states of a positronium in a spherical quantum dot

Confined states of a positronium (Ps) in the spherical quantum dot (QD) are theoretically investigated in three size-quantization (SQ) regimes: strong, weak and intermediate. In the strong SQ regime, analytical expressions for the wave functions (WFs) and energy of the electron-positron pair are obtained. In the weak SQ regime, the Ps energy and binding energy are analytically calculated. To calculate the Ps energy in the intermediate SQ regime, variational and numerical methods are used. It is shown that, in the corresponding limits, the results obtained by variational method agree with those obtained in the strong and weak SQ regimes.     

Transport of strongly comptonized radiation

For strongly Comptonized radiation in a nonrelativistic plasma, we calculate the bremsstrahlung source of Comptonized photons with an accurate allowance for free-free absorption and nonlinear stimulated Compton emission. We formulate radiation hydrodynamics equations that are valid in the limit of strong Compton energy exchange between plasma and radiation. We derive a formula for the energy dissipation rate under these conditions. For an optically thick region, we have found an equation that describes the spatial variation in the exponential fall-off factor of the radiation spectrum.     

Induced absorption of light in the magnetoelectric-photo effect in InSb: Saturation at low temperatures

An induced absorption of photons observed in an electron-hole plasma of InSb in the transverse configuration (JH) of the current density J and the magnetic field H has been demonstrated to saturate at high values of J×H at low temperatures. Nevertheless, strong emission of photons having a central wavelength corresponding to the energy gap is still observed at 80 K, suggesting generation of excess electron-hole pairs by the action of the J×H force. The mechanism of the induced absorption is also discussed.     

Microwave control of transport through a chaotic mesoscopic dot

We establish analogy between a microwave ionization of Rydberg atoms and a charge transport through a chaotic quantum dot induced by a monochromatic field in a regime with a potential barrier between dot contacts. We show that the quantum coherence leads to dynamical localization of electron excitation in energy so that only a finite number of photons is absorbed inside the dot. The theory developed determines the dependence of localization length on dot and microwave parameters showing that the microwave power can switch the dot between metallic and insulating regimes. ultiphoton ionization and excitation to highly excited states (e.g., Rydberg states)     

Microwave ponderomotive action on the inhomogeneous collisionless and collisional plasmas

The nonlinear interaction of a high-power microwave (MW) with an unmagnetized inhomogeneous plasma is investigated in collisionless and collisional regimes. The electron density distribution and the nonlinear wave equation in an inhomogeneous plasma are obtained by taking into account the ponderomotive force due to the high-power MW. It is shown that the electron density distribution becomes very steepened in the presence of the ponderomotive force. In the collisional regime, the expression for electron temperature is also found by considering ohmic heating. It is indicated that the amplitude of oscillations of the electron temperature and dielectric permittivity increases and the wavelength of these oscillations decreases with increasing energy flux, hence modulation occurs.     

Hysteresis in the presence of electron-cyclotron resonance

A method of determining the nonlinear interaction of microwaves with a magnetoactive lowpressure plasma is presented. It is shown by solving simultaneously the problems of the propagation of electromagnetic waves, the balance of charged particles, and the energy balance that near a critical value of the constant magnetic induction the character of the interaction of the wave and the plasma changes substantially: For magnetic fields above the critical field a much stronger interaction is observed, for which the penetration depth of the incident wave into the plasma increases. An investigation of the strong interaction regime showed the existence of hysteresis, which is accompanied by an abrupt transition from one standing-wave mode in plasma to another. It is shown that virtually complete absorption of the wave is possible. Zh. Tekh. Fiz. 69, 31–37 (December 1999)     

Bright side of the Coulomb blockade

We explore the photonic (bright) side of the dynamical Coulomb blockade (DCB) by measuring the radiation emitted by a dc voltage-biased Josephson junction embedded in a microwave resonator. In this regime Cooper pair tunneling is inelastic and associated with the transfer of an energy 2eV into the resonator modes. We have measured simultaneously the Cooper pair current and the photon emission rate at the resonance frequency of the resonator. Our results show two regimes, in which each tunneling Cooper pair emits either one or two photons into the resonator. The spectral properties of the emitted radiation are accounted for by an extension to DCB theory.     

The use of a hybrid model to compute the nonlinear acoustic performance of silencers for the finite amplitude acoustic wave

In the present study, a hybrid method is proposed for predicting the acoustic performance of a silencer for a nonlinear wave. This method is developed by combining two models: (i) a frequency-domain model for the computation of sound attenuation due to a silencer in a linear regime and (ii) a wavenumber space model for the prediction of the nonlinear time-evolution of finite amplitudes of the acoustic wave in a uniform duct of the same length as the silencer. The present method is proposed under the observation that the physical process of the nonlinear sound attenuation phenomenon of a silencer may be decoupled into two distinct mechanisms: (a) a linear acoustic energy loss that owes to the mismatch in the acoustic impedance between reactive elements and/or the sound absorption of acoustic liners in a silencer; (b) a nonlinear acoustic energy loss that is due to the energy-cascade phenomenon that arises from the nonlinear interaction between components of different frequencies. To establish the validity of the present model for predicting the acoustic performance of silencers, two model problems are considered. First, the performance of simple expansion mufflers with nonlinear incident waves has been predicted. Second, proposed method is applied for computing nonlinear acoustic wave propagation in the NASA Langley impedance duct configuration with ceramic tubular liner (CT57). Both results obtained from the hybrid models are compared with those from computational aero-acoustic techniques in a time-space domain that utilize a high-order finite-difference method. Through these comparisons, it is shown that there are good agreements between the two predictions. The main advantage of the present method is that it can effectively compute the nonlinear acoustic performance of silencers in nonlinear regimes without time-space domain calculations that generally entail a greater computational burden.     

Algorithm of fundamental parameters for the SEICXRF method

An algorithm based on fundamental parameters and applied to the SEICXRF method, developed by one of the authors, is presented. The methodology used in the calculation is similar to the Rousseau fundamental parameters method, but the main difference is the considerations about the x‐ray secondary fluorescence. In the new experimental method, the fluorescence yield by photons corresponding to the absorption edges with energies greater than the absorption edge energy of analyte does not occur. This secondary fluorescence appears in the calculation of the total fluorescence as a consequence of the integral count of the fluorescent emission from the sample. It is created by the primary fluorescence yield of the atoms whose absorption edge energies are less than the primary fluorescence energy of the analyte. The algorithm also considers the effect of the decrease of the sample fluorescent background just at the jump, originated by the change of the absorption coefficient at the absorption edge energy of the element of interest. Considering these two effects, including the primary fluorescence in the calculation, allows one to obtain the net fluorescence originated by the analyte at its own absorption edge. Copyright © 2003 John Wiley & Sons, Ltd.     

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用KMR模型研究了等离子体中多光子非线性Compton散射下电子相轨道的演化,发现电子与光子进行能量交换后,只有未被俘获电子的相轨道才能从周期性向非周期性、随机型演化,其演化剧烈程度随电子吸收光子数的增大而加剧,随电子与光子碰撞非弹性成分和碰撞前初始速度的增大而迅速减弱,但低于强激光场中的剧烈程度。当电子被光场俘获时,这种演化过程结束并做稳定的运动,光子不再为电子提供能量。     

Compton散射下等离子体中电子相轨道的演化

用KMR模型研究了等离子体中多光子非线性Compton散射下电子相轨道的演化,发现电子与光子进行能量交换后,只有未被俘获电子的相轨道才能从周期性向非周期性、随机型演化,其演化剧烈程度随电子吸收光子数的增大而加剧,随电子与光子碰撞非弹性成分和碰撞前初始速度的增大而迅速减弱,但低于强激光场中的剧烈程度。当电子被光场俘获时,这种演化过程结束并做稳定的运动,光子不再为电子提供能量。     

橄榄油的聚集荧光猝灭及吸收光谱特性的研究

素有“液体黄金”之称的橄榄油已成为健康食用油的代名词,不仅身价陡增,而且在非产地市场也已成为一种畅销油。在橄榄油检测技术中光谱法与其他技术相比具有快速、无损、无样品处理等优势而备受关注,而不同的光谱检测方法在检测的物质成分上各有侧重,例如红外光谱法侧重于脂肪酸含量的检测、拉曼光谱法侧重于分子的检测、荧光光谱法侧重于光敏物质的检测以及吸收光谱法侧重于光敏物质和不饱和脂肪酸的检测等。荧光及吸收光谱对光敏物质反应极其灵敏,而橄榄油富含叶绿素等光敏物质,因此荧光及吸收光谱成为一种鉴别橄榄油的有效技术手段。叶绿素是一种含有环卟啉结构的有机分子,该类分子结构具有吸光特性,且不同的叶绿素吸收光谱各异,其中绿色植物的叶绿素a含量最多。为深入研究叶绿素的吸收光谱及荧光特性在橄榄油鉴别中的应用,将特级初榨橄榄油中掺入不同比例的玉米油,已达到间接调控橄榄油中叶绿素含量的目的,测量不同掺伪比例橄榄油的荧光及吸收光谱并研究与叶绿素浓度的相关性,以此来研究叶绿素浓度与掺伪量对橄榄油吸收光谱及荧光特性的影响。取10份同批次的特级初榨橄榄油,将其中9份按照等比例稀释,并对10份样品按照掺伪量依次排序;依次采集这10份样品的荧光及吸收光谱,比较叶绿素浓度与掺伪量的相关性及对这两种光谱技术在橄榄油鉴别中的影响。随着叶绿素浓度的上升,荧光强度由弱变强,并在某一时刻后会出现荧光强度急剧减弱的现象,即聚集荧光猝灭。这种现象主要是由于叶绿素的环卟啉分子结构引起的分子间π-π作用,使未被激发的低能分子与高能分子堆叠在一起,能量的辐射跃迁（荧光）也转变为分子间的能量转移（热能交换）。对于吸收光谱,随着叶绿素浓度的上升,吸收光谱的强度也逐渐增强。橄榄油中叶绿素吸收的能量主要去向包括镁电子辐射跃迁产生荧光以及分子间热能交换两部分,而橄榄油的吸收光谱并未出现类似于聚集荧光猝灭的现象,且吸收光谱强度与掺伪浓度间存在近似线性相关的关系。结果表明：当聚集荧光猝灭出现时,叶绿素吸收的能量仍然与浓度呈线性相关,此时高、低能分子堆叠引起的热能交换效率提高。     

Optical bistability produced by resonant Joule's heating of semiconductors

The thermal hysteresis of Joule's absorption of infrared radiation in then-type semiconductor magnetoplasma is analysed. Such bistability is connected with the temperature dependence of the relaxation time of free electrons, their density being constant. The resonant Joule's absorption bistability of the pumping infrared wave near a Langmuir resonance of free electrons is discussed as well as the hysteresis cross-modulation of an infrared probing wave by means of a pumping microwave. The possibilities of smooth detuning of the hysteresis regime due to a magnetic-field control and low energy thresholds of these regimes are illustrated for InSb thin films in relatively weak magnetic fieldsH1–2 kG.     

基于EDXRF技术茶叶中金属元素检测方法研究

能量色散X射线荧光光谱(EDXRF)法作为化学元素分析的一种检测手段,被广泛应用于地质勘测、工矿石油、生化医疗及刑侦考古等各行各业,它是户外现场检测与分析的首选方法之一。利用EDXRF法检测茶叶中金属元素含量,对环境条件要求低,且无需对茶叶样品进行化学处理。实验检测发现,用该方法分析茶叶中金属元素时,有效X射线荧光光子能量段在3～16 keV之间,故校正光谱元素选择位于能量中心位置(8 keV)附近的铜元素,并用铜元素定标做标准曲线,在茶叶有效X射线荧光光子能量段中,通过样品加标方法分析铜、铁、锌、铅四种元素,求得平均检出限为1.25 mg·kg-1。在检测茶叶中金属元素的化学方法中,选用火焰原子吸收法测得茶叶中金属元素含量作为标准值,比较得出,EDXRF法测得数值实际相对误差小于6%,相对标准偏差小于5%,经过t检验,p＞0.05,说明EDXRF法与火焰原子吸收法在统计学上没有显著差异,两种方法所测结果吻合。结果表明,EDXRF法检测茶叶中金属含量的方法是可行的,结果满足现场检测分析需求。     

Shear Alfvén wave perpendicular propagation from the kinetic to the inertial regime

We report on observations of shear Alfvén waves radiated from a source of small transverse size, and the subsequent radial confinement of wave magnetic field energy within a cylindrical plasma. The radius of confinement lies between the kinetic regime of the bulk plasma and the inertial regime at the plasma edge; this radius is found to be a function of wave frequency. Numerical calculations using kinetic theory predict a zero in the perpendicular group velocity at a radius which varies in accord with the observations. An analytic expression for the perpendicular group velocity (valid for small perpendicular wave numbers) is given in the vicinity of the zero crossing.