Velocity Of Light In Vacuum Research Articles

Dynamical Essence of the Basic Relations of the Special Theory of Relativity and the Origin of Fundamental Interactions: Phenomenology

It is shown that the adoption of the hypothesis that the electromagnetic component of physical vacuum, the vacuum of quantum electrodynamics (QED vacuum), undergoes polarization in the vicinity of elementary particles allows us to comprehend, on the phenomenological level, the physical essence of the basic hypotheses of the special theory of relativity, including the nature of the limitation of the velocity of material objects to the velocity of light in vacuum. The QED vacuum here plays the part of the base medium that governs the development of the fundamental strong and gravitational interactions.

Causal propagation of nonanalytical points in fast- and slow-light media

We examined the propagation of bending nonanalytical points encoded on temporally smooth Gaussian-shaped optical pulses in fast- and slow-light media, using an optical ring resonator. For bending nonanalytical points, the pulse function is continuous, but the first-order derivative is discontinuous, in contrast to traditional nonanalytical points in which the pulse function itself is discontinuous. The nonanalytical points were neither advanced nor delayed, but appeared at the same instance as they entered the ring resonator, in good accordance with the fact that the information velocity was equal to the light velocity in vacuum or the background medium. The differences between the traditional discontinuous and the present bending nonanalytical points were investigated.

Plasmonic rainbow trapping by a graphene monolayer on a dielectric layer with a silicon grating substrate

Considering the propagation of surface plasmon polaritons (SPPs) supported by a graphene monolayer can be effectively controlled via electrostatic gating, we propose a graphene monolayer on a graded silicon-grating substrate with dielectric spacer as an interlayer for plasmonic rainbow trapping in the infrared domain. Since the dispersive relation of SPPs is dependent on the width of dielectric spacer filling the silicon grating, the guided SPPs at different frequencies can be localized at different positions along the graphene surface, associated with the period of silicon grating. The group velocity of slow SPPs can be made to be several hundred times smaller than light velocity in vacuum. We also predict the capability of completely releasing the trapped SPPs by dynamically tuning the chemical potential of graphene by means of gate voltage. The advantages of such a structure include compact size, wide frequency tunability, and compatibility with current micro/nanofabrication, which holds great promise for applications in graphene-based optoelectronic devices.

Proposal of Coupled Ring Resonator Based on One-Dimensional Photonic Crystal Nanocavity

We propose the coupled ring resonator based on one-dimensional photonic crystal (1-D PC) nanocavity. The proposed structure is composed by introducing 1-D PC nanocavity into the CROW based on ring resonator, and we expect that it can achieve small group velocity. We investigate the transmission characteristics of the proposed structure by using 2-D scalar finite element method (FEM) for periodic waveguide analysis. We obtained the group velocity vg = 0.033 c with c being light velocity in vacuum because of combining 1-D PC nanocavity and CROW based on ring resonator. Moreover, we consider reduction of footprint of the proposed structure for photonic integration.

Tight focusing of radially polarized vortex laser pulse

The tight focusing of femtosecond radially polarized vortex laser pulse by a high numerical aperture objective is investigated in this paper. Based on Richards-Wolf vectorial diffraction theory, the electric field and the group velocity of the radially polarized vortex femtosecond laser pulse are studied in great detail. It finds that the femtosecond radially polarized vortex laser pulse can travel at various group velocities near the focus, that is, slower or faster than light velocity in vacuum, depending on the numerical aperture of the focusing objective system. Moreover, the effect of spherical aberration of objective, topological charge and time duration of the radially polarized vortex laser pulse on the group velocity distribution near the focus is discussed.

Slow light in photonic crystal with combinations of gradient dielectric constant

A line defect waveguide formed by a new kind of two-dimensional photonic crystal with combinations of gradient varied dielectric was designed and the properties of slow light will been studied by using the Plane Wave expansion Method (PWM). The result shows that the group velocity is slower when the corresponding combination of gradient dielectric constants are with higher dielectric constant and lower interval. In our new structure of photonic crystal, the corresponding group velocity can reach as low as 0.06c (c: light velocity in vacuum), two orders magnitude lower than light velocity. Meanwhile, the group velocity dispersion effect is relatively small.

Special Theory of Relativity Postulated on Homogeneity of Space and Time and on Relativity Principle

In Special Theory of Relativity time is considered to be the 4th dimension of space – time as a consequence of Lorentz invariance and Minkowski metric, in turn based on the invariance of light speed . In this paper we’ll show that, starting only from universal postulates as homogeneity of space and time and Principle of Relativity, we can obtain space and time transformations (as the Lorentz and Tangherlini – Selleri ones) characterized by an invariant speed generally different than . These results determine crucial difficulties in the assumption of Minkowski metric and consequently in the interpretation of physical time as the 4th component of space – time, also introducing a “relativity” feature in the velocity of light in vacuum being no longer considerable as a necessarily universal invariant quantity and depending on the physical properties of space which originate from quantum vacuum. A novel interpretation of time, coherent with these results, defined as duration of material change in space, i.e. motion, is finally proposed.

Neutrinos with velocities greater thanc?

A possible explanation of the results of the OPERA experiment is presented. Assuming that the usual value of c should be interpreted as the velocity of light in dark matter, we call the "true" velocity of light in vacuum, $c_t$. Then the OPERA neutrinos can be faster than c but slower than $c_t$. We also discuss the relationship between $c_t$ and neutrino masses.

Causal information velocity in fast and slow pulse propagation in an optical ring resonator

We examined the propagation of nonanalytical points encoded on temporally Gaussian-shaped optical pulses in fast and slow light in an optical ring resonator at $\ensuremath{\lambda}$ = 1.5 \ensuremath{\mu}m. The temporal peak of the Gaussian pulse was either advanced or delayed, reflecting anomalous or normal dispersions in the ring resonator, relevant to under- or overcoupling conditions, respectively. The nonanalytical points were neither advanced nor delayed but appeared as they entered the ring resonator. The nonanalytical points could be interpreted as information; therefore, the experimental results suggested that information velocity is equal to the light velocity in vacuum or the background medium, independent of the group velocity. The transient behaviors at the leading and trailing edges of the nonanalytical points are discussed in terms of optical precursors.

Average and instantaneous velocities of energy of evanescent modes

Many theoretical and experimental investigations have concluded that evanescent electromagnetic modes can propagate superluminally. However, in this paper we show that the average energy velocity of evanescent modes inside a cutoff waveguide is always less than or equal to the velocity of light in vacuum, while the instantaneous energy velocity can be superluminal, which does not violate causality according to quantum field theory: the fact that a particle can propagate over a spacelike interval does preserve causality provided that a measurement performed at one point cannot affect another measurement at a point separated from the first with a spacelike interval.

Engineering the light propagating features through the two-dimensional coupled-cavity photonic crystal waveguides

This paper studies the propagating characteristics of the electromagnetic waves through the coupled-resonator optical waveguides based on the two-dimensional square-lattice photonic crystals by the finite-difference time-domain method. When the traditional circular rods adjacent to the centre of the cavities are replaced by the oval rods, the simulated results show that the waveguide mode region can be adjusted only by the alteration of the oval rods' obliquity. When the obliquity of the oval rods around one cavity is different from the obliquity of that around the adjacent cavities, the group velocities of the waveguide modes can be greatly reduced and the information of different frequencies can be shared and chosen at the same time by the waveguide branches with different structures. If the obliquities of the oval rods around two adjacent cavities are equal and they alternate between two values, the group velocities can be further reduced and a maximum value of 0.0008c (c is the light velocity in vacuum) can be acquired.

Velocity and velocity bounds in static spherically symmetric metrics

Abstract We find simple expressions for velocity of massless particles with dependence on the distance, r, in Schwarzschild coordinates. For massive particles these expressions give an upper bound for the velocity. Our results apply to static spherically symmetric metrics. We use these results to calculate the velocity for different cases: Schwarzschild, Schwarzschild-de Sitter and Reissner-Nordström with and without the cosmological constant. We emphasize the differences between the behavior of the velocity in the different metrics and find that in cases with naked singularity there always exists a region where the massless particle moves with a velocity greater than the velocity of light in vacuum. In the case of Reissner-Nordström-de Sitter we completely characterize the velocity and the metric in an algebraic way. We contrast the case of classical naked singularities with naked singularities emerging from metric inspired by noncommutative geometry where the radial velocity never exceeds one. Furthermore, we solve the Einstein equations for a constant and polytropic density profile and calculate the radial velocity of a photon moving in spaces with interior metric. The polytropic case of radial velocity displays an unexpected variation bounded by a local minimum and maximum.

Experimental study of the electron beam compressed state breakup

The dynamics of breakup of the compressed state of an electron beam with a virtual cathode (VC) transported in a two-section drift tube of a high-current electron accelerator has been studied. Based on the results of numerical simulations, the method of partial capture of the injected beam current during the applied voltage pulse is proposed and implemented, which can ensure the conditions necessary for the breakup of the electron beam compressed state. The VC velocity during the breakup of the electron beam compressed state amounts to 6–8% of the velocity of light in vacuum. The experimental data qualitatively agree with the results of analytical estimations and numerical simulations.

Ab initio study of the bandgap engineering of Al1−xGaxN for optoelectronic applications

A theoretical study of Al1−xGaxN, based on the full-potential linearized augmented plane wave method, is used to investigate the variations in the bandgap, optical properties, and nonlinear behavior of the compound with the change in the Ga concentration. It is found that the bandgap decreases with the increase in Ga. A maximum value of 5.50 eV is determined for the bandgap of pure AlN, which reaches a minimum value of 3.0 eV when Al is completely replaced by Ga. The static index of refraction and dielectric constant decreases with the increase in the bandgap of the material, assigning a high index of refraction to pure GaN when compared to pure AlN. The refractive index drops below 1 for higher energy photons, larger than 14 eV. The group velocity of these photons is larger than the vacuum velocity of light. This astonishing result shows that at higher energies the optical properties of the material shifts from linear to nonlinear. Furthermore, frequency dependent reflectivity and absorption coefficients show that peak values of the absorption coefficient and reflectivity shift toward lower energy in the ultraviolet (UV) spectrum with the increase in Ga concentration. This comprehensive theoretical study of the optoelectronic properties predicts that the material can be effectively used in the optical devices working in the visible and UV spectrum.

Mssbauer experiments in a rotating system on the time dilation effect

In this contribution, we analyze both the old Mossbauer experiments in a rotating system and our new experiment on this subject, which unambiguously indicate the presence of an additional component in the relative energy shift DE/E between emission and absorption lines, as compared with the classic relativistic expression written to the accuracy c-2 (that is DE/E=-u2/2c2, where u is the tangential velocity of absorber, and c the light velocity in vacuum). The additional dilation of time for the rotating absorber constitutes more than 20% from the relativistic value, and it many times exceeds the measuring uncertainty. We discuss a possible origin of this effect and the ways of its further experimental verification. Key words: Relativistic dilation of time, rotating systems, Mossbauer effect.

Stimulated Raman scattering of laser in heavily doped semiconductors

An intense short pulse laser propagating through a heavily doped degenerate semiconductor, parametrically excites a free carrier space charge mode and back scattered electromagnetic mode via free carrier nonlinearity. Landau damping and collisional damping of the decay waves determine the threshold for the instability. Above the threshold, the growth rate scales as γ∼(v0/2c)(εLωω0)1/2, where v0 is the free carrier oscillatory velocity, c is the velocity of light in vacuum, εL is the lattice permittivity, ω is the frequency of the space charge mode, and ω0 is the pump frequency.

Tight-binding photonic bands in metallophotonic waveguide networks and flat bands in kagome lattices

We propose that we can realize "tight-binding photonic bands" in metallophotonic waveguide networks, where the photonic bound states localized around the crossings of a network form a tight-binding band. The formation of bound states at the crossings is distinct from the conventional bound states at defects or virtual bound states in photonic crystals, but comes from a photonic counterpart of the zero-point states in wave mechanics. Model calculations show that the low-lying photon dispersions are indeed described accurately by the tight-binding model. To exemplify how we can exploit the tight-binding analogy for a {\it designing} of photonic bands, we propose a "flat photonic band" in the kagome network, in which the photonic flat band is shown to arise with group velocities that can be as small as 1/1000 times the velocity of light in vacuum.

Enhanced parametric amplification in slow-light photonic crystal waveguides

We demonstrate both theoretically and numerically that slow light can enhance the parametric process of silicon in photonic crystal line-defect waveguides. Specifically, to get the desired gain, the pump power for a given gain medium length or the gain medium length for given pump power can be reduced by (c/v g n)2 when slow light waveguides are used, where n is the material index of conventional waveguide, v g is the group velocity of the slow light waveguide and c is the light velocity in vacuum.

A Mössbauer experiment in a rotating system on the second-order Doppler shift: confirmation of the corrected result by Kündig

We present the results of a Mössbauer experiment in a rotating system, whose performance was stimulated by our recent findings (2008 Phys. Scr. 77 035302) and which consisted of the fact that a correct processing of Kündig's experimental data on the subject gives an appreciable deviation of a relative energy shift ΔE/E between emission and absorption resonant lines from the standard prediction based on the relativistic dilation of time (that is, ΔE/E=−v2/2c2 to the accuracy c−2, where v is the tangential velocity of the absorber of resonant radiation, and c is the velocity of light in vacuum). That is, the Kündig result we have corrected becomes ΔE/E=−k(v2/c2), with k=0.596±0.006 (instead of the result k=0.5003±0.006, originally reported by Kündig). In our own experiment, we carried out measurements for two absorbers with a substantially different isomer shift, which allowed us to make a correction of the Mössbauer data regarding vibrations in the rotor system at various rotational frequencies. As a result, we obtained the overall estimation k=0.68±0.03.

Sequential Operations of Quantum Dot/Photonic Crystal All-Optical Switch With High Repetitive Frequency Pumping

A photonic crystal (PC)-based symmetric Mach-Zehnder type all-optical switch (PC-SMZ), previously operated by single pump pulse alone, has been operated newly by a multiple-pump pulse train corresponding to a repetition frequency of 40 GHz at pulse energy as low as 10 fJ. The device involves quantum dots (QDs) in two parallel PC arms as optical nonlinear media and functions as a time-differential phase modulator caused by the pump pulse inducing carriers in the QD. Prior to the switch operation, sequential time response of the phase shift for a probe pulse was investigated in detail by changing the power and repetition rate of the pump pulse in the straight PC waveguide configuration. Besides, PC and QD parameters were explored for possibility of 100% on-off switching ratio. As a result, five QD layers, 40-ps QD relaxation-time, 500-mum PC-length and use of as low as 0.05 c PC group-velocity (c; light velocity in vacuum) were found to implement the 100% switching ratio. Since each of these parameters has ever been achieved experimentally, the result will pave a promising way to an ultra-small and ultra-fast integrated all-optical switch.