scholarly journals A bound on the group velocity for Bloch wave packets

2015 ◽  
Vol 72 (2) ◽  
pp. 119-123
Author(s):  
Grégoire Allaire ◽  
Mariapia Palombaro ◽  
Jeffrey Rauch
Keyword(s):  
Group Velocity ◽  
Wave Packets ◽  
Bloch Wave

Interferometric (Fourier-Spectroscopic) Measurement of Electron Energy Distributions

1990 ◽  
Vol 48 (2) ◽  
pp. 110-111 ◽  
Author(s):  
F. Hasselbach ◽  
A. Schäfer
Keyword(s):  
Group Velocity ◽  
Wave Packets ◽  
Index Of Refraction ◽  
Electron Wave ◽  
Fringe Contrast ◽  
Faraday Cage ◽  
Optical Index ◽  
Wien Filter ◽  
Coherent Wave ◽  
Electric And Magnetic Fields

Möllenstedt and Wohland proposed in 1980 two methods for measuring the coherence lengths of electron wave packets interferometrically by observing interference fringe contrast in dependence on the longitudinal shift of the wave packets. In both cases an electron beam is split by an electron optical biprism into two coherent wave packets, and subsequently both packets travel part of their way to the interference plane in regions of different electric potential, either in a Faraday cage (Fig. 1a) or in a Wien filter (crossed electric and magnetic fields, Fig. 1b). In the Faraday cage the phase and group velocity of the upper beam (Fig.1a) is retarded or accelerated according to the cage potential. In the Wien filter the group velocity of both beams varies with its excitation while the phase velocity remains unchanged. The phase of the electron wave is not affected at all in the compensated state of the Wien filter since the electron optical index of refraction in this state equals 1 inside and outside of the Wien filter.

scholarly journals Optical wave-packet with nearly-programmable group velocities

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Zhaoyang Li ◽  
Junji Kawanaka
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Wave Packets ◽  
Bessel Beam ◽  
Propagation Path ◽  
Uniform Motion ◽  
Optical Wave ◽  
Straight Line ◽  
Line Trajectory ◽  
Group Velocities

AbstractDuring the process of Bessel beam generation in free space, spatiotemporal optical wave-packets with tunable group velocities and accelerations can be created by deforming pulse-fronts of injected pulsed beams. So far, only one determined motion form (superluminal or luminal or subluminal for the case of group velocity; and accelerating or uniform-motion or decelerating for the case of acceleration) could be achieved in a single propagation path. Here we show that deformed pulse-fronts with well-designed axisymmetric distributions (unlike conical and spherical pulse-fronts used in previous studies) allow us to obtain nearly-programmable group velocities with several different motion forms in a single propagation path. Our simulation shows that this unusual optical wave-packet can propagate at alternating superluminal and subluminal group velocities along a straight-line trajectory with corresponding instantaneous accelerations that vary periodically between positive (acceleration) and negative (deceleration) values, almost encompassing all motion forms of the group velocity in a single propagation path. Such unusual optical wave-packets with nearly-programmable group velocities may offer new opportunities for optical and physical applications.

scholarly journals Acoustic Bloch wave energy transport and group velocity

1991 ◽  
Vol 89 (4B) ◽  
pp. 1971-1971
Author(s):  
Charles E. Bradley ◽  
David T. Blackstock
Keyword(s):  
Group Velocity ◽  
Wave Energy ◽  
Energy Transport ◽  
Bloch Wave

Acoustic Behavior of Near Periodic Elastic Structures

1995 ◽  
Author(s):  
Douglas M. Photiadis
Keyword(s):  
Cross Section ◽  
Wave Packets ◽  
Acoustic Scattering ◽  
Direct Interaction ◽  
Bloch Wave ◽  
Acoustic Properties ◽  
Theoretical Development ◽  
Naval Research ◽  
Bragg Scattering ◽  
Elastic Structures

Abstract Near periodic arrays of discontinuities have been predicted to have a significant impact on the acoustic properties of elastic structures. The discontinuities in the elastic properties of the structure produce a characteristic signature in the acoustic scattering cross section of the structure via two distinct mechanisms; a direct interaction producing acoustic Bragg scattering, and an indirect interaction wherein the discontinuities fundamentally alter the free waves of the structure. The locally propagating states of the pseudo-periodic system are Floquet or Bloch wave packets and the locations of the highlights in the cross section may be determined simply from the Bloch wavenumber via a phase matching argument. Predicting the resulting scattering levels requires an understanding of the propagation of the Bloch wave packets in the finite, pseudo-periodic structure. In the case of a thin ribbed cylindrical shell or plate this scattering mechanism can arise from flexural waves, and recent experimental results obtained at Naval Research Laboratory have demonstrated the importance of both this mechanism and Bragg scattering on the acoustic far field over a broad frequency range. In this paper, these results and the underlying theoretical development will be discussed.

A Nonlinear Multiscale Theory of Atmospheric Blocking: Eastward and Upward Propagation and Energy Dispersion of Tropospheric Blocking Wave Packets

2020 ◽  
Vol 77 (12) ◽  
pp. 4025-4049
Author(s):  
Dehai Luo ◽  
Wenqi Zhang
Keyword(s):  
Group Velocity ◽  
Growth Phase ◽  
Wave Packets ◽  
Finite Amplitude ◽  
Wave Activity ◽  
Amplitude Equation ◽  
Planetary Waves ◽  
Decay Phase ◽  
Upper Troposphere ◽  
Envelope Amplitude

AbstractIn this paper, a nonlinear multiscale interaction model is used to examine how the planetary waves associated with eddy-driven blocking wave packets propagate through the troposphere in vertically varying weak baroclinic basic westerly winds (BWWs). Using this model, a new one-dimensional finite-amplitude local wave activity flux (WAF) is formulated, which consists of linear WAF related to linear group velocity and local eddy-induced WAF related to the modulus amplitude of blocking envelope amplitude and its zonal nonuniform phase. It is found that the local eddy-induced WAF reduces the divergence (convergence) of linear WAF in the blocking upstream (downstream) side to favor blocking during the blocking growth phase. But during the blocking decay phase, enhanced WAF convergence occurs in the blocking downstream region and in the upper troposphere when BWW is stronger in the upper troposphere than in the lower troposphere, which leads to enhanced upward-propagating tropospheric wave activity, though the linear WAF plays a major role. In contrast, the downward propagation of planetary waves may be seen in the troposphere for vertically decreased BWWs. These are not seen for a zonally uniform eddy forcing. A perturbed inverse scattering transform method is used to solve the blocking envelope amplitude equation. It is found that the finite-amplitude WAF represents a modified group velocity related to the variations of blocking soliton amplitude and zonal wavenumber caused by local eddy forcing. Using this amplitude equation solution, it is revealed that, under local eddy forcing, the blocking wave packet tends to be nearly nondispersive during its growth phase but strongly dispersive during the decay phase for vertically increased BWWs, leading to strong eastward and upward propagation of planetary waves in the downstream troposphere.

scholarly journals The effects of trapped and untrapped particles on an electrostatic wave packet

1974 ◽  
Vol 12 (3) ◽  
pp. 487-500 ◽  
Author(s):  
Magne S. Espedal
Keyword(s):  
Wave Equation ◽  
Wave Packet ◽  
Group Velocity ◽  
Wave Packets ◽  
Particle Interaction ◽  
Finite Amplitude ◽  
Amplitude Wave ◽  
Electrostatic Wave ◽  
Wave Particle Interaction ◽  
Poisson Equations

We present a procedure to solve the Vlasov–Poisson equations for electrostatic wave packets. We obtain a Schrödinger type of wave equation, taking the wave– particle interaction into account. We use this equation to study the propagation of one finite-amplitude wave packet. We find a change in amplitude caused by interaction between the packet and particles propagating near to the group velocity. Also, we find a modulation of the plasma in the front of the packet, caused by trapping effects.

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