Light In Vacuum Research Articles

An Implicit and Untested Premise of the Special Theory of Relativity

The derivation of Lorentz Transformation Equations in the Special Theory of Relativity, besides being explicitly based on the two postulates of that theory is also critically based on an implicit premise that the detection of a light signal/particle at a point in space at an instant of time is an event that is not exclusive to any inertial reference frame but it is capable of being measured by the observers in other inertial reference frames as well. This paper explains how this untested paradoxical premise vitiates the entire theory and suggests its replacement with a contrary postulate that the detection of light in an inertial reference frame is an event that is exclusive to that frame. This paper shows that if that contrary postulate is accepted, then the absoluteness of space and time declared by Newton can coexist with the absoluteness of the speed of light in vacuum declared by Einstein without any conflict between them.

Quantum Speed Limit for Relativistic Spin-0 and Spin-1 Bosons on Commutative and Noncommutative Planes

Quantum speed limits of relativistic charged spin-0 and spin-1 bosons in the background of a homogeneous magnetic field are studied on both commutative and noncommutative planes. We show that, on the commutative plane, the average speeds of wave packets along the radial direction during the interval in which a quantum state is evolving from an initial state to the orthogonal final one can not exceed the speed of light, regardless of the intensities of the magnetic field. However, due to the noncommutativity, the average speeds of the wave packets on noncommutative plane will exceed the speed of light in vacuum provided the intensity of the magnetic field is strong enough. It is a clear signature of violating Lorentz invariance in the relativistic quantum mechanics region.

对应于铯原子D1线正交压缩真空态光场的制备

对应于铯原子D₁线正交压缩真空态光场的制备

压缩真空光输入和光子计数法增强Sagnac效应

压缩真空光输入和光子计数法增强Sagnac效应

On the distortion of the rising edge of a carrier-free signal

The 1D problem related to the distortion of the rising edge of a carrier-free signal, which arise abruptly at the starting point, is examined. It is demonstrated that, in propagation through an arbitrary (including, absorbing) medium, the signal’s rising edge is not distorted and moves exactly with the speed of light in vacuum. Signals are revealed to attenuate with growing path length. Such attenuation occurs due to shortening of the time interval on which the rising part of the signal continues to hold its initial value without a decrease in its initial amplitude. The given time interval has been estimated.

Tunable Negative Group Delay in a Birefringent Fabry–Pérot-Like Cavity With High Fractional Advancement Induced by Cross-Interference Effect

A strong and broadband negative group delay (NGD) is demonstrated in a circular waveguide with an asymmetric cross-shaped slotted structure in the millimeter-wave region. For an input of 45° linear polarization (relative to the orientation of the cross-shaped slots), the NGD fractional bandwidth is as high as 3.57%, in which the optimal group advancement obtained is nearly 24 times greater than the delay traveling with the speed of light in vacuum. This further indicates a very high fractional advancement of 12.10%. In addition, the NGD can be controlled by adjusting the polarization azimuthal angle of the incident pulse. The observed tunable NGD effect is attributed to the destructive cross interference between the two polarization eigenstates, which effectively reduces the released field energy at the observed polarization channel. A general theory is provided with excellent agreement in the experimental and simulation results.

Momentum conservation in a relativistic engine

In a previous paper we have shown that Newton’s third law cannot strictly hold in a distributed system of which the different parts are at a finite distance from each other. This is due to the finite speed of signal propagation which cannot exceed the speed of light in vacuum, which in turn means that when summing the total force in the system the force does not add up to zero. This was demonstrated in a specific example of two current loops with time-dependent currents, the above analysis led to the suggestion of a relativistic engine. Since the system is affected by a total force for a finite period of time this means that the system acquires momentum, the question then arises if we need to abandon the law of momentum conservation. In this paper we make a detailed calculation and show that any momentum gained by the material part of the system is equal in magnitude and opposite in direction to the momentum gained by the electromagnetic field. Hence the total momentum of the system is conserved.

Phase mixing of relativistically intense longitudinal wave packets in a cold plasma

Phase mixing of relativistically intense longitudinal wave packets in a cold homogeneous unmagnetized plasma has been studied analytically and numerically using the Dawson Sheet Model. A general expression for phase mixing time (ωptmix) as a function of amplitude of the wave packet (δ) and width of the spectrum (Δk/k) has been derived. It is found that the phase mixing time crucially depends on the relative magnitude of amplitude “δ” and the spectral width “Δk/k”. For Δk/k≤2ωp2δ2/c2k2, ωptmix scales with δ as ∼1/δ5, whereas for Δk/k>2ωp2δ2/c2k2, ωptmix scales with δ as ∼1/δ3, where ωp is the non-relativistic plasma frequency and c is the speed of light in vacuum. We have also verified the above theoretical scalings using numerical simulations based on the Dawson Sheet Model.

Euclidean Closed Linear Transformations of Complex Spacetime and generally of Complex Spaces of dimension four endowed with the Same or Different Metric

Relativity Theory and the corresponding Relativistic Quantum Mechanics are the fundamental theories of physics. Special Relativity (SR) relates the frames of Relativistic Inertial observers (RIOs), through Linear Spacetime Transformation (LSTT) of linear spacetime. Classic Special Relativity uses real spacetime endowed with Lorentz metric and the frames of two RIOs with parallel spatial axes are always related through Lorentz Boost (LB). This cancels the transitive attribute in parallelism, when three RIOs are related, because LB is not closed transformation, causing Thomas Rotation. In this presentation, we consider closed LSTT of Complex Spacetime, so there is no necessity for spatial axes rotation and all the frames are chosen having parallel spatial axes. The solution is expressed by a 4x4 matrix (Λ) containing components of the complex velocity of one Observer wrt another and two functions depended by the metric of Spacetime. Demanding isometric transformation, it emerges a class of metrics that are in accordance with the closed LSTT and the transformation matrix contains one parameter ω depended by the metric of Spacetime. In case that we relate RIOs with steady metric, it emerges one steady number (ωI) depended by the metric of Spacetime of the specific SR. If ωI is an imaginary number, the elements of the Λ are complex numbers, so the corresponding spacetime is necessarily complex and there exists real Universal Speed (UI). The specific value ωI=±i gives Vossos transformation (VT) endowed with Lorentz metric (for gii=1) of complex spacetime and invariant spacetime interval (or equivalently invariant speed of light in vacuum), which produce the theory of Euclidean Complex Relativistic Mechanics (ECRMs). If ωI is a real number (ωI#0) the elements of the Λ are real numbers, so the corresponding spacetime is real, but there exist imaginary UI. The specific value ωI=0 gives Galileo Transformation (GT) with the invariant time, in which any other closed LSTT is reduced, if one RIO has small velocity wrt another RIO. Thus, we have infinite number of closed LSTTs, each one with the corresponding SR theory. In case that we relate accelerated observers with variable metric of spacetime, we have the case of General Relativity (GR). For being that clear, we produce a generalized Schwarzschild metric, which is in accordance with any SR based on this closed complex LSTT and Einstein equations. The application of this kind of transformations to the SR and GR is obvious. But, the results may be applied to any linear space of dimension four endowed with steady or variable metric, whose elements (four- vectors) have spatial part (vector) with Euclidean metric.

Rise-Time Distortion of Signal without Carrying Signal

The article deals with one-dimensional problem of rise-time distortion signal without carrying signal, that appears in the starting point intermittently, that is signal distortion at front edge or one of its derivative. The authors show that front edge of signal isn't distorted in case of propagation in unrestricted (including absorbing) area (amplitude of starting signal step or of one of its derivatives doesn't change) and move with the accuracy of vacuum light speed. The paper proves that it is the time interval shortage that causes signal loss with the route extension, but not the reduction of its starting amplitude, during which front edge of signal retains its starting value. The research presents new values for this time interval.

Light speed variation from gamma ray burst GRB 160509A

It is postulated in Einstein's relativity that the speed of light in vacuum is a constant for all observers. However, the effect of quantum gravity could bring an energy dependence of light speed. Even a tiny speed variation, when amplified by the cosmological distance, may be revealed by the observed time lags between photons with different energies from astrophysical sources. From the newly detected long gamma ray burst GRB~160509A, we find evidence to support the prediction for a linear form modification of light speed in cosmological space.

Wideband slow-light propagation with no distortion in a nanofiber-plane-grating composite waveguide

A nanofiber-plane-grating composite slow-light waveguide to achieve wideband slowlight propagation with no distortion is proposed. The waveguide is formed by embedding a tapered nanofiber into a V-groove on a plane-grating surface. By optimizing the waveguide structural parameters, a slow-light effect with bandwidth of about 1453 GHz is obtained. Based on finite-difference time-domain (FDTD) method, we analyze the waveguide’s optical properties and slow-light characteristics. Simulation results show that a picosecond optical pulse propagating in the slow-light waveguide can be delayed for about 980 fs and without distortion. The group velocity of the optical pulse can be reduced to about 0.3c (c is the speed of light in vacuum). This study will provide important theoretical basis and innovative ideas for the development of new-type slow-light elements.

On possible origin of an anisotropy in the speed of light in vacuum

We assume the spacetime foam picture in which vacuum is filled with virtual wormholes. In the presence of an external field the distribution of wormholes changes. We consider an anisotropic distribution of wormholes and analyze its relation to the speed of light. We show that speed of light acquires an anisotropic character and save the normal dispersion a gas of virtual wormholes may possess also an anomalous dispersion, i.e., when the light velocity exceeds that in the vacuum.

Statistical dispersion relation for spatially broadband fields.

The dispersion relation is fundamental to a physical phenomenon that develops in both space and time. This equation connects the spatial and temporal frequencies involved in the dynamic process through the material constants. Electromagnetic plane waves propagating in homogeneous media are bound by simple dispersion relation, which sets the magnitude of the spatial frequency, k, as being proportional to the temporal frequency, ω, with the proportionality constant dependent on the refractive index, n, and the speed of light in vacuum, c. Here we show that, for spatially broadband fields, an analog dispersion relation can be derived, except in this case the k-vector variance is connected with the temporal frequency through the statistics of the refractive index fluctuations in the medium. We discuss how this relationship can be used to retrieve information about refractive index distributions in biological tissues. This result is particularly significant in measurements of angular light scattering and quantitative phase imaging of biological structures.

Response of a mechanical oscillator in an optomechanical cavity driven by a finite-bandwidth squeezed vacuum excitation

In this paper, we theoretically investigate the displacement and momentum fluctuations spectra of the movable mirror in a standard optomechanical system driven by a finite bandwidth squeezed vacuum light accompanying a coherent laser field. Two cases in which the squeezed vacuum is generated by degenerated and non-degenerate parametric oscillators (DPO and NDPO) are considered. We find that for the case of finite bandwidth squeezed vacuum injection, the two spectra exhibit unique features, which strongly differ from those of broadband squeezing excitation. In particular, the spectra exhibit a three-peaked and a four-peaked structure, respectively, for the squeezing injection from DPO and NDPO. Besides, some anomalous characteristics of the spectra such as squeezing-induced pimple, hole burning, and dispersive profile are found to be highly sensitive to the squeezing parameters and the temperature of the mirror. We also evaluate the mean-square fluctuations in position and momentum quadratures of the movable mirror and analyze the influence of the squeezing parameters of the input field on the mechanical squeezing. It will be shown that the parameters of driven squeezed vacuum affects the squeezing. We find the optimal mechanical squeezing is achievable via finite bandwidth squeezed vacuum injection which is affected by the intensity of squeezed vacuum. We also show that the phase of incident squeezed vacuum determines whether position or momentum squeezing occurs. Our proposed scheme not only provides a feasible experimental method to detect and characterize squeezed light by optomechanical systems, but also suggests a way for controllable transfer of squeezing from an optical field to a mechanical oscillator.

Gamma rays as probes of the Universe

The propagation of γ rays over very large distances provides new insights on the intergalactic medium and on fundamental physics. On their path to the Earth, γ rays can annihilate with diffuse infrared or optical photons of the intergalactic medium, producing e+e− pairs. The density of these photons is poorly determined by direct measurements due to significant galactic foregrounds. Studying the absorption of γ rays from extragalactic sources at different distances allows the density of low-energy diffuse photons to be measured. Gamma-ray propagation may also be affected by new phenomena predicted by extensions of the Standard Model of particle physics. Lorentz Invariance is violated in some models of Quantum Gravity, leading to an energy-dependent speed of light in vacuum. From differential time-of-flight measurements of the most distant γ-ray bursts and of flaring active galactic nuclei, lower bounds have been set on the energy scale of Quantum Gravity. Another effect that may alter γ-ray propagation is predicted by some models of String Theory, namely the mixing of the γ ray with a light fundamental boson called an “axion-like particle”, which does not interact with low-energy photons. Such a mixing would make the Universe more transparent to γ rays than what would otherwise be, in a sense it decreases the amount of modification to the spectrum that comes from the extragalactic background light. The present status of the search for all these phenomena in γ-ray astronomy is reviewed. La propagation des photons γ sur de très grandes distances nous permet de sonder le milieu intergalactique et fournit des tests de physique fondamentale. Au cours de leur chemin vers la Terre, ceux-ci peuvent s'annihiler avec les photons infrarouges et optiques du milieu intergalactique, produisant ainsi des paires e+e−. L'absorption des photons γ émis par des sources extragalactiques à différentes distances permet de mesurer ce fond diffus, par ailleurs très mal connu par des mesures directes en raison des importants rayonnements d'avant-plan dus à la Galaxie. La propagation des photons γ peut aussi être affectée par de nouveaux phénomènes prédits par des extensions du modèle standard de la physique des particules. L'invariance de Lorentz est violée dans certains modèles de gravité quantique où la vitesse de la lumière dans le vide varie avec l'énergie du photon γ. Les mesures différentielles de temps de vol sur les sursauts γ et sur les éruptions de noyaux actifs de galaxie ont permis d'obtenir des bornes inférieures sur l'échelle d'énergie de la gravité quantique. Un autre effet pouvant affecter la propagation des photons γ est prédit par des modèles de la théorie des cordes. Il s'agit du mélange quantique entre le photon et une particule légère de type « axion », qui n'interagit pas avec les photons infrarouge et optiques. En diminuant dans les spectres l'empreinte de l'absorption par le fond diffus, ce mélange rendrait l'Univers plus transparent que prévu aux photons γ. L'article présente l'état actuel des recherches sur l'ensemble de ces phénomènes en astronomie γ

Acceleration of electrons by a laser pulse at its output onto an optical surface of the vacuum – transparent medium interface. Laser synchrotron

We consider the electron dynamics in the field of an electromagnetic wave produced at the vacuum – transparent medium interface upon reflection from the boundary, close to total internal reflection. The propagation velocity of a constant phase of the electromagnetic wave along the interface can vary from to infinity ( is the speed of light in vacuum, and is the refractive index of the medium at the interface). In this case, there emerge regions of positive and negative phases of the field with wavelengths, approximately equal to half the wavelength of the original laser beam, which can propagate at a speed close to that of light in vacuum. If a beam of relativistic electrons propagates along the surface, they can gain energy and accelerate, as well as radiate. With closed trajectories of electron motion, a laser synchrotron will be implemented as a result of many acceleration cycles.

Slow light in dual-periodic photonic crystals based slotted-waveguide coupled cavity

Considering the capacity of the nanoscale width area with the low-refractive index can confine light waves, the dual-periodic slotted photonic crystals, which is constructed by coupling low-refractive index's slotted-waveguide with high-refractive index's cavity is proposed in this paper. The best slow light properties and the optimal slotted-waveguide coupled cavity are achieved by adjusting the slotted-width and the period of cavity respectively. In this structure, the slow-light properties are simulated by Plane Wave Expansion (PWE), the result reveals that the group velocities are all three orders of magnitude smaller than the speed of light in vacuum, the slowest value is 7.96×10−4c when the slotted-width is 0.54a and the period of cavity is 0.95a. Moreover, the corresponding Normalized Delay-Bandwidth Product (NDBP) values are larger than 0.24. Besides, the slotted-waveguide coupled cavity can be reconfigured, which accordingly changes the corresponding slow-light property. At last, the numerical results provide a new thought and method for decreasing group velocity and potential application for optical buffer in photonic crystals field.

Radiation pressure acceleration: The factors limiting maximum attainable ion energy

Radiation pressure acceleration (RPA) is a highly efficient mechanism of laser-driven ion acceleration, with near complete transfer of the laser energy to the ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable ion energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansion of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansion, the areal density of the target decreases, making it transparent for radiation and effectively terminating the acceleration. The off-normal incidence of the laser on the target, due either to the experimental setup, or to the deformation of the target, will also lead to establishing a limit on maximum ion energy.

Stimulated Raman scattering in hydrogen by ultrashort laser pulse in the keV regime

This letter addresses the problem of stimulated Raman excitation of a hydrogen atom submitted to an ultrashort and intense laser pulse in the keV regime. The pulse central frequency ω of 55 a.u. (about 1.5 keV) is in the weakly relativistic regime, (c is the speed of light in vacuum and a0 the Bohr radius) and the pulse duration is τ ≈ 18.85 a.u. (about 456 attoseconds). We solve the corresponding time-dependent Schrödinger equation (TDSE) using a spectral approach, retardation (or nondipole) effects are included up to , breaking the conservation of the magnetic quantum number m and forcing the resolution of the TDSE in a three-dimensional space. Due to the laser bandwidth, which is of the order of the ionization potential of hydrogen, stimulated Raman scattering populates nlm excited states (n and l are the principal and azimuthal quantum numbers, respectively). The populations of these excited states are calculated and analyzed in terms of l and m quantum numbers, this showing the contributions of the retardation effects and their relative importance.