On the reality of supraluminal group velocity and negative delay time for a wave packet in a dispersion medium

2002 ◽  
Vol 47 (1) ◽  
pp. 132-134 ◽  
Author(s):  
N. S. Bukhman
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Delay Time ◽  
Dispersion Medium ◽  
Negative Delay

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 Statistical characteristics of AGW wave packet propagation in the lower atmosphere observed by the MU radar

2009 ◽  
Vol 27 (10) ◽  
pp. 3737-3753 ◽  
Author(s):  
F. S. Kuo ◽  
H. Y. Lue ◽  
C. L. Fern ◽  
J. Röttger ◽  
S. Fukao ◽  
...  
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Wave Period ◽  
Lower Atmosphere ◽  
Statistical Characteristics ◽  
Data Set ◽  
Horizontal Structure ◽  
North West ◽  
Mu Radar ◽  
Upward Moving

Abstract. We study the horizontal structure of the atmospheric gravity waves (AGW) in the height ranges between 6 and 22 km observed using the MU radar at Shigaraki in Japan, during a 3 day period in January and a 4 day period in August 1988. The data were divided by double Fourier transformation into a data set of upward moving waves and a data set of downward moving waves for independent analysis. The phase and group velocity tracing technique was applied to measure the vertical group and phase velocity as well as the characteristic period of the gravity wave packet. Then the dispersion equation of the linear theory of AGW was solved to obtain its intrinsic wave period – horizontal wavelength and horizontal group velocity – and the vertical flux of horizontal momentum associated with each wave packet was estimated to help determine the direction of the characteristic horizontal wave vector. The results showed that the waves with periods in the range of 30 min~6 h had horizontal scales ranging from 20 km to 1500 km, vertical scales from 4 km to 15 km, and horizontal phase velocities from 15 m/s to 60 m/s. The upward moving wave packets of wave period of 2 h~6 h had horizontal group velocities mainly toward east-south-east and northeast in winter, and mainly in the section between the directions of west-north-west and north in summer.

Application-Oriented Ray Theory

1978 ◽  
Vol 15 (3) ◽  
pp. 215-223 ◽  
Author(s):  
Dan Censor
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Dispersion Equation ◽  
Electrical Engineering ◽  
Ray Theory ◽  
Velocity Wave ◽  
The Subject ◽  
Fermat’S Principle ◽  
Equation Group ◽  
Fermat's Principle

This is a tutorial presentation of the subject of ray theory as provided for third-year students of electrical engineering. The concepts of the eikonal and dispersion equation, group velocity, wave packet, Fermat's principle and the ray equations are introduced. This is essential for students majoring in electromagnetic engineering.

Intramode wave packet in a thin left-handed film with the spectrum near the frequency of the zero group velocity

2016 ◽  
Vol 46 (11) ◽  
pp. 1040-1046 ◽  
Author(s):  
D A Konkin ◽  
R V Litvinov ◽  
E S Parfenova ◽  
Rakhim R.A.A. ◽  
O V Stukach
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Left Handed ◽  
Zero Group

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.

Total reflection cannot occur with a negative delay time

2001 ◽  
Vol 37 (6) ◽  
pp. 794-799 ◽  
Author(s):  
K.J. Resch ◽  
J.S. Lundeen ◽  
A.M. Steinberg
Keyword(s):  
Delay Time ◽  
Total Reflection ◽  
Negative Delay

On the Group Front and Group Velocity in a Dispersive Medium Upon Refraction From a Nondispersive Medium

2003 ◽  
Author(s):  
Z. M. Zhang ◽  
Keunhan Park
Keyword(s):  
Wave Packet ◽  
Phase Velocity ◽  
Wave Front ◽  
Group Velocity ◽  
Dispersive Medium ◽  
Front Velocity ◽  
Normal Group ◽  
Nondispersive Medium ◽  
Positive Index ◽  
Front Movement

Conventional definitions of the velocities associated with the propagation of the modulated wave are both confusing and insufficient to describe the behavior of the wave packet clearly in a multi-dimensional dispersive medium. There exist infinite solutions to the general equation of wave-front movement, suggesting that there are infinite phase velocities. Therefore, the introduction of “normal phase velocity” becomes necessary to unambiguously define the phase velocity in the direction perpendicular to the wave front. Similarly, there exist infinite solutions to the equation describing the group-front movement in the case of a wave packet, resulting in infinite “group-front velocities.” The “normal group-front velocity” is defined as the smallest speed at which the group-front travels and is in the direction perpendicular to the group front. We show that the group velocity (i.e., the velocity of energy flow) is one of the group-front velocities and, in general, is not the same as the normal group-front velocity. Hence, the direction in which the wave packet travels is not necessarily normal to the group front. Examples are used to demonstrate the behavior of a wave packet that is refracted from vacuum to a positive index medium (PIM) or a negative index medium (NIM).

scholarly journals Phase and group velocity tracing analysis of projected wave packet motion along oblique radar beams – qualitative analysis of QP echoes

2007 ◽  
Vol 25 (1) ◽  
pp. 77-86 ◽  
Author(s):  
F. S. Kuo ◽  
H. Y. Lue ◽  
C. L. Fern
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Gravity Waves ◽  
Theoretical Calculations ◽  
Wave Packets ◽  
Wave Length ◽  
Wave Period ◽  
Horizontal Distance ◽  
Characteristic Wave ◽  
Horizontal Wave

Abstract. The wave packets of atmospheric gravity waves were numerically generated, with a given characteristic wave period, horizontal wave length and projection mean wind along the horizontal wave vector. Their projection phase and group velocities along the oblique radar beam (vpr and vgr), with different zenith angle θ and azimuth angle φ, were analyzed by the method of phase- and group-velocity tracing. The results were consistent with the theoretical calculations derived by the dispersion relation, reconfirming the accuracy of the method of analysis. The RTI plot of the numerical wave packets were similar to the striation patterns of the QP echoes from the FAI irregularity region. We propose that the striation range rate of the QP echo is equal to the radial phase velocity vpr, and the slope of the energy line across the neighboring striations is equal to the radial group velocity vgr of the wave packet; the horizontal distance between two neighboring striations is equal to the characteristic wave period τ. Then, one can inversely calculate all the properties of the gravity wave responsible for the appearance of the QP echoes. We found that the possibility of some QP echoes being generated by the gravity waves originated from lower altitudes cannot be ruled out.

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