Superluminal Wave Propagation Research Articles

Anomalous to normal dispersion nonlinear optical dephasing switch in electromagnetically induced transparency using a Kerr effect

The atomic decoherence effect (DE) on a Kerr nonlinear (KNL) electromagnetically induced transparency (EIT)is studied in a Δ system. The DE between the ground state hyperfine levels is caused by the dephasing rate γ d which dramatically modifies the medium response. It controls the normal dispersive region which shows steep positive slopes for linear response at the line center while the nonlinear response experiences steep negative slopes for low γ d . The microwave field strength and γ d modify the nonlinear response from the anomalous dispersion to normal dispersion. The calculations show that room-temperature atoms are used to quantify the quantum interference (QI) on linear and nonlinear absorption with γ d . The EIT spectrum explores the understanding of the subluminal and superluminal wave propagation of probe signal and this study opens a new pathway for the understanding of the QI devices and their nonlinearities based on EIT.

Superluminal wave propagation in a non‐Foster negative capacitor loaded transmission line

Superluminal wave propagation phenomenon achieved from a periodic structure in which a transmission line (TL) is loaded with non-Foster negative capacitors is presented. The loading decreases the effective capacitance and the effective permittivity of the dielectric substrate of the TL. An experimental investigation of the superluminal phase and group velocity in the non-Foster loaded TL is reported. The phase and group velocities are extracted from measured S-parameters. To do so, three non-Foster negative capacitors operating over [50–350 MHz] frequency band are integrated in a TL. Superluminal broadband effects are obtained from 50 to 220 MHz. The negative capacitors loaded TL paves the way to innovative broadband leaky wave antennas, active metamaterial surfaces and cloaking devices.

Controlling the superluminal

controlling the superluminal

Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet’s Tale

I outline, from a theoretical and somewhat personal perspective, significant features of Pulsar Wind Nebulae as Cosmic Accelerators. I discuss recent studies of Pulsar Wind Nebulae (PWNe). I pay special attention to the recently discovered gamma ray flares in the Crab Nebula's emission, focusing on the possibility, raised by the observations, that the accelerating electric field exceeds the magnetic field, suggesting that reconnection in the persistent current layer (a current sheet) plays a significant role in the behavior of this well studied Pevatron. I address the present status of the termination shock model for the particle accelerator that converts the wind flow energy to the observed non thermal particle spectra, concluding that it has a number of major difficulties related to the transverse magnetic geometry of the shock wave. I discuss recent work on the inferred pair outflow rates, which are in excess of those predicted by existing theories of pair creation, and use those results to point out that the consequent mass loading of the wind reduces the wind's bulk flow 4-velocity to the point that dissipation of the magnetic field in a pulsar's wind upstream of the termination shock is restored to life as a viable model for the solution of the "sigma problem". I discuss some suggestions that current starvation in the current flow supporting the structured ("striped") upstream magnetic field induces a transition to superluminal wave propagation. I show that current starvation probably does not occur, because those currents are carried in the current sheet separating there stripes rather than in the stripes themselves.

Temporally Advanced Signal Detection: A Review of the Technology and Potential Applications

In recent years, a physical phenomenon referred to as Negative Group Delay (NGD) or superluminal wave propagation has been implemented in electronic circuitry and shown to temporally advance the detection of analog signals. Specifically, the output of such a circuit precedes the complete detection of its input as the group (and therefore time) delay through the circuit is negative. In this article we describe the background and theory behind this phenomenon, discuss its implementation in electronics and demonstrate a specific biomedical signal application (the human ECG). We discuss some key NGD circuit design considerations/configurations and potential applications in which this technology could offset or eliminate entirely, closed-loop control system delays.

A Systemized View of Superluminal Wave Propagation

This paper reviews earlier studies on superluminal wave propagation in anomalously dispersive media that have been carried out in the electronic, microwave, and optical regimes. Those studies are relevant to observation of modulated Gaussian pulses transmitted through various media at speeds apparently faster than c without distortion. This paper also presents the condition for superluminal propagation that is established based on the magnitude-phase relation of a causal and minimum-phase filter. Since the condition is modeled on the basis of filter theory, it is applicable to all types of media. A terahertz experiment with a periodic bandgap structure is also included to illustrate superluminal propagation.

Prolog to A Systemized View of Superluminal Wave Propagation

Prolog to "A Systemized View of Superluminal Wave Propagation."

Tachyonic γ-ray bursts generated by nonlocal plasma currents

The dispersion relations of superluminal wave propagation in electron plasmas are derived, and the tachyonic energy flux, the velocity of energy transport, and the relaxation time asymptotics of the conductivity are studied. The formalism is based on Maxwell-type equations for Proca fields with negative mass-square in dispersive and dissipative media. Specifically, superluminal radiation fields generated by the ultra-relativistic electronic source plasma of γ-ray bursts (GRBs) are investigated. The radiation field is coupled to the shock-heated electron gas by a frequency-dependent fine-structure constant. The varying coupling constant generates long-range dispersion in the charge and current densities. At high energy, the coupling strength approaches a finite limit, so that the Proca field becomes minimally coupled to the electron current. The tachyonic fine-structure constant scales with the frequency-dependent superluminal velocity of the radiated modes. This scaling is manifested in the tachyonic flux densities of the GRB plasma, so that the scaling exponent can be extracted from spectral maps in the soft γ-ray band. To this end, tachyonic spectral fits of GRB 930506, GRB 950425, and GRB 910503 are performed. The scaling amplitude of the fine-structure constant is inferred from the burst duration. The transversal and longitudinal tachyonic luminosity of the source plasma is calculated in the high-temperature regime. Estimates of the plasma temperature and the internal energy of the ultra-relativistic electron gas are obtained.

Tachyons in the Milne universe

Superluminal particles (tachyons) are studied in a Robertson-Walker cosmology with linear expansion factor and negatively curved 3-space (Milne universe). This cosmology admits globally geodesic rest frames for uniformly moving observers, isometric copies of the forward lightcone, which can be synchronized by Lorentz boosts. We investigate superluminal wave propagation, a real Proca field with negative mass-square, coupled to subluminal matter in analogy to the electromagnetic field. For photons, the eikonal approximation is exact in Robertson-Walker cosmology, and the Proca field is coupled to the background geometry in such a way that this also holds for tachyons. The spectral decomposition of freely propagating tachyon fields in the Milne universe is derived. We study the wave-particle duality in terms of the spectral elementary waves and their orthogonal ray bundles, in the comoving frame as well as in the individual geodesic rest frames of galactic observers. The spectral energy density of a tachyon background radiation is discussed.