In this work, we theoretically investigate the superluminal and subluminal reflected group delay from an air-Weyl semimetal film-Weyl semimetal substrate layered structure by using 4*4 magneto-optical matrix. We show a tunable transition between positive and negative group delays of reflection pulse in such a layered structure controlled by the properties of the Weyl Semimetal layer and reveal its mechanism to control the propagation properties of the light pulse reflected from such structure. It is demonstrated that the reflected group delays are tunable from positive to negative values and vice versa, which are adjusted by tuning the incident angle, thickness of Weyl semimetal film, tilt parameter, and Fermi energy. The control of the magnitude and the sign of the reflected group delay of light propagation represent a key point in slow and fast light technologies. Our results are helpful to control the pulse propagations and are useful for design of Weyl semimetal-based delay devices.
The relativistic aberration of a wavevector and the corresponding Doppler shift are examined in connection with superluminal and subluminal spatiotemporally localized pulsed optical waves. The requirement of a null Doppler shift is shown to give rise to a speed associated with the relativistic velocity composition law of a double (two-step) Lorentz transformation. The effects of such a transformation are examined both in terms of four-coordinates and in the spectral domain. It is established that a subluminal pulse reverses its direction. In addition to a change in direction, the propagation t…
We study the influence of the angle between the two dipole transition moments on the group velocity for two kinds of three-level V-type systems with spontaneously generated coherence and incoherent pumping. The group velocity of the probe field for both kinds of the V-type systems alternates between the subluminal or superluminal regimen. We can choose a real three-level V-type system from atoms or molecules to exhibit subluminal or superluminal light propagation by a proper geometry of the probe, coupling and incoherent pumping fields, which depends on the angle between the two dipole transit…
We investigate the behavior of light pulse propagation in a 4-level double Lambda atomic system under condition of electromagnetically induced transparency. The Fano type interference effect and spectral hole burning appears in the the dynamics of the absorption-dispersion spectra caused by the joint nonlinear coherence Kerr effect and Doppler broadening. The coherent Kerr effect exhibits an enhancement (reduction) in superluminal (subluminal) in negative (in positive) group index while the Doppler broadening generates multiple hole burning in the Autler-Townes like spectra of this system. The…
We study the change of the probe field group velocity from subluminal to superluminal range for two kinds of closed three-level V-type system with spontaneously generated coherence and incoherent pumping field. For the first kind of the V-type system we deduce the analytical formula of the group velocity, while for the second kind of the V-type system we solve numerically the density matrix equations system and apply it to a real system from the LiH molecule. We find that the group index of the probe field can be changed from positive to negative within the appropriate choice of the relative p…
A universal relation has been established between the local energy transport velocity along the direction of propagation and the group velocity of scalar and vector-valued propagation-invariant spatiotemporally localized superluminal and subluminal electromagnetic waves in free space. Under specific restrictions, this relationship is very closely valid for physically realizable almost propagation-invariant spatiotemporally confined subluminal and superluminal electromagnetic fields. In both cases, although the group velocity may be either superluminal or subluminal, the universal relation is i…
It is well known that although the group velocity of structured light pulses propagating in vacuum can be subluminal or superluminal, the upper limit of the energy flow velocity is c, the speed of light in vacuum. This inequality can be explained in terms of the reactive energy left behind by the fields. Energy and reactive energy densities have been calculated for vector-valued two-dimensional (light sheet) superluminal electromagnetic nondiffractive pulses, as well as scalar-valued and TM three-dimensional superluminal and subluminal spatiotemporally localized electromagnetic waves. Emphasis…
We consider pulse propagation through a two component composite medium (metal inclusions in a dielectric host) with or without cavity mirrors. We show that a very thin slab of such a medium, under conditions of localized plasmon resonance, can lead to significant superluminality with detectable levels of transmitted pulse. A cavity containing the heterogeneous medium is shown to lead to subluminal-to-superluminal transmission depending on the volume fraction of the metal inclusions. The predictions of phase time calculations are verified by explicit calculations of the transmitted pulse shapes…
We theoretically investigate the response of optical phase conjugators to incident probe pulses. In the stable (sub-threshold) operating regime of an optical phase conjugator it is possible to transmit probe pulses with a superluminally advanced peak, whereas conjugate reflection is always subluminal. In the unstable (above-threshold) regime, superluminal response occurs both in reflection and in transmission, at times preceding the onset of exponential growth due to the instability.
The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence (SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying a…
We consider an optomechanical double-ended cavity under the action of a coupling laser and a probe laser in electromagnetically induced transparency configuration. It is shown how the group delay and advance of the probe field can be controlled by the power of the coupling field. In contrast to single-ended cavities, only allowing for superluminal propagation, possibility of both superluminal and subluminal propagation regimes are found. The magnitudes of the group delay and the advance are calculated to be 1ms and -2s, respectively, at a very low pumping power of a few microwatts. In addition…
We study Chiral Based Electromagnetically Induced Transparency (CBEIT) of a light pulse and its associated subluminal and superluminal behavior through a cold and a hot medium of 4-level \textit{double-Lambda type} atomic system. The dynamical behavior of this chiral based system is temperature dependent. The magnetic field based chirality and dispersion is always opposite as compared with the electric field ones. Contrastingly, the response of the chiral effect along with the incoherence Doppler broadening mechanism enhances the superluminal behavior as compared with its traditional degrading…
We analyze the propagation of a pulse across a vacuum gap separating opposite flat parallel faces of two transparent dielectrics by means of an explicitly causal and retarded propagator constructed directly from the free-space wave equation. Nevertheless, our approach yields apparently superluminal propagation for the case of frustrated total internal reflection (FTIR), that is, a transmitted wave packet appears on the far side of the gap at the same time that the corresponding incident packet crosses the front one. Thus, in this example superluminality is just an illusion, being consistent wi…
Recently, a series of theoretical and experimental papers on free-space propagation of pulsed Laguerre-Gaussian and Bessel beams was published, which reached contradictory and controversial results about group velocities of such pulses. Depending on themeasurement scheme, the group velocity can be defined differently.We analyze how different versions of group velocity are related to the measurable travel time (time of flight) of the pulse between input (source) and output (detecting) planes. The analysis is tested on a theoretical model---the Bessel-Gauss pulse whose propagation path exhibits …
Transverse (Hall-effect) and Goos--Hänchen shifts of light beams reflected/refracted at planar interfaces are important wave phenomena, which can be significantly modified and enhanced by the presence of intrinsic orbital angular momentum (OAM) in the beam. Recently, optical spatiotemporal vortex pulses (STVPs) carrying a purely transverse intrinsic OAM were predicted theoretically and generated experimentally. Here we consider the reflection and refraction of such pulses at a planar isotropic interface. We find theoretically and confirm numerically novel types of the OAM-dependent transverse …
Modulation of the optical index by means of atomic and material resonances provides a basis for controlling light propagation in natural and artificially fabricated materials. In addition, recent advances in the tuning of spatiotemporal couplings of ultrashort laser pulses have enabled almost arbitrary control over the group velocity of light. Here, using femtosecond time-resolved microscopy and numerical calculations, we investigate the spatiotemporal dynamics of a surface plasmon polariton wave packet (SPP WP) that interacts with a plasmonic nanocavity. The nanocavity consists of metal-insul…
We investigate the absorption and transmission properties of a weak probe field under the influence of a strong control field in a hybrid cavity magnomechanical system in the microwave regime. This hybrid system consists of two ferromagnetic material yttrium iron garnet (YIG) spheres strongly coupled to a single cavity mode. In addition to two magnon-induced transparency (MIT) that arise due to strong photon-magnon interactions, we observe a magnomechanically induced transparency (MMIT) due to the presence of nonlinear phonon-magnon interaction. In addition, we discuss the emergence and tunabi…
