On the theory of wave packets

In this paper we discuss some aspects of the theory of wave packets. We consider a popular noncovariant Gaussian model used in various applications and show that it predicts too slow a longitudinal dispersion rate for relativistic particles. We revise this approach by considering a covariant model of Gaussian wave packets, and examine our results by inspecting a wave packet of arbitrary form. A general formula for the time dependence of the dispersion of a wave packet of arbitrary form is found. Finally, we give a transparent interpretation of the disappearance of the wave function over time due to the dispersion—a feature often considered undesirable, but which is unavoidable for wave packets. We find, starting from simple examples, proceeding with their generalizations and finally by considering the continuity equation, that the integral over time of both the flux and probability densities are asymptotically proportional to the factor 1/|x|² in the rest frame of the wave packet, just as in the case of an ensemble of classical particles.     

On diffraction of radiation packets with ultimately short duration

The inference of the work by V.A. Banakh that there is an absence of diffraction of optical radiation in the limit of zero pulse duration is analyzed.     

一个解决声纳系统同频干扰的新思路

多平台联合作战将是未来海上作战的重要形式之一,多部主动声纳的同时存在使声兼容问题十分突出。由于友舰直达波经历的是单程传播,其强度往往比经历了双程传播的目标回波大的多。通过波形设计可以获得相关系数小的声纳波形,虽然可以从一定程度上缓解声兼容问题,但由于获得的增益有限,并不能从根本上解决这一问题。本文通过对常规检测器的修正,引入能量归一化的概念,有效地消除了能量对检测器的影响,从而解决了这一问题。同时本文还提出了与现有声纳信号处理体系相兼容的频域实现方法,使该算法在工程上的实现成为可能。计算机仿真证明,这一方法是正确有效的。     

On the collapse of wave packets in a medium with normal group velocity dispersion

A solution to the problem of realizing the collapse of three-dimensional wave packets in nonlinear media with normal group velocity dispersion is proposed. Wave packets with pronounced hyperbolic topology are shown to collapse; i.e., the field increases infinitely near the system axis. In particular, wave collapse of the tubular axisymmetric packets occurs through the concentration of the compressed ring field distribution at the axis. The collapse is shown to stabilize due to the saturation of nonlinearity or nonlinear dissipation, which restrict the field increase and lead to the packet splitting in the transverse direction.     

On the asymptotics of multidimensional linear wave packets: Reference solutions

The classic problem of linear wave-packet propagation in a dispersive medium is considered. Asymptotic equations of the Cauchy problem for two-dimensional Gaussian wave packets are constructed in terms of Fourier integrals. These asymptotic solutions are regular at the caustics and describe new physical features of wave-packet propagation: rotation in space and formation of a wave front with anomalously slow dispersion (quasi-dispersive).     

On the radiation pressure of electromagnetic wave packets in nondispersive fluid dielectrics

Using the classical dipole representation for the gas molecules, an approximate kinetic equation is derived including radiation pressure forces. The energy-momentum tensor for a quasimonochromatic electromagnetic wave packet is constructed. Electrostrictive forces and nonlinear perturbations of the gas rest energy density are taken into account. Certain particle-like properties of the wave packet are demonstrated. Radiation pressure forces are given for some simple models of fluid inhomogeneities.     

On the radiation pressure effects of two-dimensional electromagnetic wave packets in fluids

Some characteristic properties of the two-dimensional wave packet propagation across an abrupt plasma-vacuum and dielectric fluid-vacuum boundary are deduced. The momentum left behind the wave packet is found. It is shown, that the momentum localisation and distribution is other and more complicated, than it has been supposed previously.The author thanks R.Klíma for numerous discussions.     

脉冲激光频域干涉技术在超快动力学物理中的应用

介绍了一种具有fs时间分辨力的超短脉冲激光频域干涉测试技术,详细论述了该技术的工作原理和系统构成,指出传输时间差和相位差是影响频域干涉条纹周期的主要因素。采用脉冲激光频域干涉仪测量了200 nm厚度铝膜在波长800 nm、单脉冲能量0.7 mJ、脉宽35 fs脉冲激光作用下的运动速度剖面。在单次飞秒脉冲激光作用下,铝膜自由面的运动速度峰值可达960 m/s,速度剖面的上升前沿小于5.77 ps,表明脉冲激光频域干涉技术可用于测量材料在超快脉冲激光作用下的冲击动力学参数。     

脉冲激光频域干涉技术在超快动力学物理中的应用

介绍了一种具有fs时间分辨力的超短脉冲激光频域干涉测试技术,详细论述了该技术的工作原理和系统构成,指出传输时间差和相位差是影响频域干涉条纹周期的主要因素。采用脉冲激光频域干涉仪测量了200 nm厚度铝膜在波长800 nm、单脉冲能量0.7 mJ、脉宽35 fs脉冲激光作用下的运动速度剖面。在单次飞秒脉冲激光作用下,铝膜自由面的运动速度峰值可达960 m/s,速度剖面的上升前沿小于5.77 ps,表明脉冲激光频域干涉技术可用于测量材料在超快脉冲激光作用下的冲击动力学参数。     

Production and use of an interferometric optical strain gauge with comparison to conventional techniques

The use of optical fibres in transducers has recently attracted much interest and the adoption of optical techniques in strain detection is growing due to the reliability and accuracy they can offer in harsh environmental conditions (strong electromagnetic fields, high temperature, corrosive chemicals, etc.) where the conventional electrical strain gauges often fail.In this paper an optical strain gauge based on a true fibre Michelson interferometric scheme is developed and tested. The discrete optical strain gauge is realised by embedding the optical fibre sensing leads into a resin support which allows its easy installation and use. The related static and dynamic behaviours are investigated and compared with those of similar optical sensing systems either directly bonded to the structure or embedded in composite laminates. Comparisons are also made with theoretical predictions and measurements supplied by semiconductor electrical strain gauges.     

Application of Feynman propagators to the motion of one-dimensional wave packets

Presented at the International Workshop on Squeezed and Correlated States, Moscow, December 3–7, 1990.     

Generation of soliton-like wave packets and wave packets with linear phase modulation in gaining optical wave-guides with saturable nonlinearity

We have considered the dynamics of soliton-like pulses and stable frequency-modulated self-similar pulses in an active medium with saturable nonlinearity and a parabolic refractive-index profile. We show that, based on gaining gradient fibers with a parabolic distribution of the refractive index and saturable nonlinearity, it is possible to create complexes that ensure generation of laser pulses with a high (above 1 TW) peak power.     

Generation of 40-GHz control signals from flag pulses for switching all-optical gates for use with optical packets

We demonstrate an all-optical circuit capable of generating 40-GHz control signals from flag pulses that can be used to define the switching state of all-optical gates for use with optical packets. The circuit comprises a Fabry-Perot filter and a semiconductor optical amplifier, and with a single pulse it can generate 12 control pulses with 0.64-dB amplitude modulation. With two and three flag pulses the number of control pulses becomes 36 and 54, respectively.     

Spatial control of recollision wave packets with attosecond precision

We propose orthogonally polarized two-color laser pulses to steer tunneling electrons with attosecond precision around the ion core. We numerically demonstrate that the angles of birth and recollision, the recollision energy, and the temporal structure of the recolliding wave packet can be controlled without stabilization of the carrier-envelope phase of the laser, and that the wave packet's properties can be described by classical relations for a point charge. This establishes unique mapping between parameters of the laser field and attributes of the recolliding wave packet. The method is capable of probing ionic wave packet dynamics with attosecond resolution from an adjustable direction and might be used as an alternative to aligning molecules. Shaping the properties of the recollision wave packet by controlling the laser field may also provide new routes for improvement of attosecond pulse generation via high harmonic radiation.     

Drift theory of the resonant interaction of charged particles with wave packets

Averaged equations of motion are obtained for charged particles resonantly interacting with high-frequency wave packets in the case of finite cyclotron radius. It is shown that the mean action of the packet on the particle is not a potential function. Cherenkov resonance of particles with the beats of two wave packets in inhomogeneous plasma is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 10–13, April, 1982.     

Correlated use of characterization techniques to optimize the Mg implantation annealing for self-aligned HBT''s

The annealing process of Mg-implanted GaAs/GaAlAs HBT's has been optimized using different analysis techniques. The Mg activation was deduced from a comparison between the atomic profile determined by SIMS and the electrical profile determined by electrochemical C-V profiling. Under the optimum annealing conditions, a record activation value of 87% was reached. Cathodoluminescence analysis has also been used to assess the quality of the implanted materials.     

Interaction of atomic wave packets with four-wave mixing: detection of rubidium and potassium wave packets by coherent ultraviolet emission

The observation of an atomic wave packet by use of a coherent, nonlinear-optical process is reported. Wave packets formed in K or Rb vapor by two-photon excitation of ns and (n-2)dstates (n=8 for K; n=11 , 12 for Rb) with red (~620-nm) , 80-100-fs pulses were detected by four-wave mixing in pump-probe experiments. The temporal behavior of the wave packet is observed by monitoring the coherent UV radiation generated near the alkali mp(2)P? (2)S(1/2) (7相似文献   

Relativistic wave packets in the quantum field approach to the theory of neutrino oscillations

A covariant theory of wave packets and its application to the quantum field method of calculation of the probabilities of neutrino oscillations in vacuum that is based on the technique of macroscopic Feynman diagrams, which describe the processes of emission and absorption of virtual massive neutrinos ν _i (i = 1, 2, 3) at macroscopicly separated space-time points, is considered. The effect of flavor oscillations is reduced to an interference of amplitudes with different vi in an intermediate state. A macroscopic amplitude is calculated that describes a class of processes which go with nonconservation of leptonic numbers, and statistical averaging of the squared modulus of this amplitude is performed. The averaged probability of a process with ultrarelativistic neutrino exchange is representable in the form of an integral of the product of three factors: the flux of massless neutrinos from the source, the differential cross-section for the interaction of a neutrino with the detector, and a dimensionless factor that describes the flavor transition. The conditions under which the last factor can be interpreted as the probability of the flavor transition in the conventional quantummechanical sense are analyzed.