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Ayman F Abouraddy - One of the best experts on this subject based on the ideXlab platform.

  • Optical space-time wave packets having arbitrary group velocities in free space
    Nature Communications, 2019
    Co-Authors: H. Esat Kondakci, Ayman F Abouraddy
    Abstract:

    Controlling the group velocity of Light in free space has been limited to small deviations so far. Here, the authors present a method to control the spatio-temporal spectrum and allow arbitrary group velocities of a wave packet in free space both above and below the Speed of Light. Controlling the group velocity of an optical pulse typically requires traversing a material or structure whose dispersion is judiciously crafted. Alternatively, the group velocity can be modified in free space by spatially structuring the beam profile, but the realizable deviation from the Speed of Light in vacuum is small. Here we demonstrate precise and versatile control over the group velocity of a propagation-invariant optical wave packet in free space through sculpting its spatio-temporal spectrum. By jointly modulating the spatial and temporal degrees of freedom, arbitrary group velocities are unambiguously observed in free space above or below the Speed of Light in vacuum, whether in the forward direction propagating away from the source or even traveling backwards towards it.

  • space time wave packets that travel in optical materials at the Speed of Light in vacuum
    Optica, 2019
    Co-Authors: Basanta Bhaduri, Murat Yessenov, Ayman F Abouraddy
    Abstract:

    Can an optical pulse traverse a non-dispersive material at the Speed of Light in vacuum? Because traditional approaches for controlling the group velocity of Light manipulate either the material or structural resonances, an absence of dispersion altogether appears to exclude such a prospect. Here we demonstrate theoretically and experimentally that “space–time” wave packets—pulsed beams in which the spatial and temporal degrees of freedom are tightly intertwined—can indeed traverse a non-dispersive transparent optical material at the Speed of Light in vacuum. We synthesize wave packets whose spatio-temporal spectra lie along the intersection of the material’s Light-cone with a spectral hyperplane tilted to coincide with the vacuum Light-line. By measuring the group delay interferometrically with respect to a generic reference pulse, we confirm that the wave packet group velocity in a variety of materials (including water, glass, and sapphire) is the Speed of Light in vacuum.

  • optical space time wave packets having arbitrary group velocities in free space
    arXiv: Optics, 2018
    Co-Authors: Esat H Kondakci, Ayman F Abouraddy
    Abstract:

    Controlling the group velocity of an optical pulse typically requires traversing a material or structure whose dispersion is judiciously crafted. Alternatively, the group velocity can be modified in free space by spatially structuring the beam profile, but the realizable deviation from the Speed of Light in vacuum is small. Here we demonstrate precise and versatile control over the group velocity of a propagation-invariant optical wave packet in free space through sculpting its spatio-temporal spectrum. By jointly modulating the spatial and temporal degrees of freedom, arbitrary group velocities are unambiguously observed in free space above or below the Speed of Light in vacuum, whether in the forward direction propagating away from the source or even traveling backwards towards it.

Bhola N. Dwivedi - One of the best experts on this subject based on the ideXlab platform.

  • Gravitational redshift and the vacuum index of refraction
    Astrophysics and Space Science, 2019
    Co-Authors: Klaus Wilhelm, Bhola N. Dwivedi
    Abstract:

    A physical process of the gravitational redshift was described in an earlier paper (Wilhelm and Dwivedi, New Astron. 31:8, 2014 ). This process did not require any information for the emitting atom neither on the local gravitational potential  U $U$ nor on the Speed of Light  c $c$ . Although it could be shown that the correct energy shift of the emitted photon resulted from energy and momentum conservation principles and the Speed of Light at the emission site, it was not obvious how this Speed is controlled by the gravitational potential. The aim of this paper is to describe a physical process that can accomplish this control. We determine the local Speed of Light  c $c$ by deducing a gravitational index of refraction  n G $n_{\mathrm{G}}$ as a function of the potential  U $U$ assuming a specific aether model, in which photons propagate as solitons. Even though an atom cannot locally sense the gravitational potential  U $U$ (cf. Müller et al., Nature 467:E2, 2010 ) the gravitational redshift will nevertheless be determined by  U $U$ (cf. Wolf et al., Nature 467:E1, 2010 )—mediated by the local Speed of Light  c $c$ .

  • gravitational redshift and the vacuum index of refraction
    arXiv: General Physics, 2017
    Co-Authors: Klaus Wilhelm, Bhola N. Dwivedi
    Abstract:

    A physical process of the gravitational redshift was described in an earlier paper (Wilhelm & Dwivedi 2014) that did not require any information for the emitting atom neither on the local gravitational potential U nor on the Speed of Light c. Although it could be shown that the correct energy shift of the emitted photon resulted from energy and momentum conservation principles and the Speed of Light at the emission site, it was not obvious how this Speed is controlled by the gravitational potential. The aim of this paper is to describe a physical process that can accomplish this control. We determine the local Speed of Light c by deducing a gravitational index of refraction nG as a function of the potential U assuming a specific aether model, in which photons propagate as solitons. Even though an atom cannot locally sense the gravitational potential U (cf. Muller et al. 2010), the gravitational redshift will nevertheless be determined by U (cf. Wolf et al. 2010)- mediated by the local Speed of Light c.

Germano Nardini - One of the best experts on this subject based on the ideXlab platform.

  • bounding the Speed of gravity with gravitational wave observations
    Physical Review Letters, 2017
    Co-Authors: Neil J. Cornish, Diego Blas, Germano Nardini
    Abstract:

    The time delay between gravitational wave signals arriving at widely separated detectors can be used to place upper and lower bounds on the Speed of gravitational wave propagation. Using a Bayesian approach that combines the first three gravitational wave detections reported by the LIGO Scientific and Virgo Collaborations we constrain the gravitational waves propagation Speed c_{gw} to the 90% credible interval 0.55cSpeed of Light in vacuum. These bounds will improve as more detections are made and as more detectors join the worldwide network. of order 20 detections by the two LIGO detectors will constrain the Speed of gravity to within 20% of the Speed of Light, while just five detections by the LIGO-Virgo-Kagra network will constrain the Speed of gravity to within 1% of the Speed of Light.

Basanta Bhaduri - One of the best experts on this subject based on the ideXlab platform.

  • space time wave packets that travel in optical materials at the Speed of Light in vacuum
    Optica, 2019
    Co-Authors: Basanta Bhaduri, Murat Yessenov, Ayman F Abouraddy
    Abstract:

    Can an optical pulse traverse a non-dispersive material at the Speed of Light in vacuum? Because traditional approaches for controlling the group velocity of Light manipulate either the material or structural resonances, an absence of dispersion altogether appears to exclude such a prospect. Here we demonstrate theoretically and experimentally that “space–time” wave packets—pulsed beams in which the spatial and temporal degrees of freedom are tightly intertwined—can indeed traverse a non-dispersive transparent optical material at the Speed of Light in vacuum. We synthesize wave packets whose spatio-temporal spectra lie along the intersection of the material’s Light-cone with a spectral hyperplane tilted to coincide with the vacuum Light-line. By measuring the group delay interferometrically with respect to a generic reference pulse, we confirm that the wave packet group velocity in a variety of materials (including water, glass, and sapphire) is the Speed of Light in vacuum.

H. Esat Kondakci - One of the best experts on this subject based on the ideXlab platform.

  • Optical space-time wave packets having arbitrary group velocities in free space
    Nature Communications, 2019
    Co-Authors: H. Esat Kondakci, Ayman F Abouraddy
    Abstract:

    Controlling the group velocity of Light in free space has been limited to small deviations so far. Here, the authors present a method to control the spatio-temporal spectrum and allow arbitrary group velocities of a wave packet in free space both above and below the Speed of Light. Controlling the group velocity of an optical pulse typically requires traversing a material or structure whose dispersion is judiciously crafted. Alternatively, the group velocity can be modified in free space by spatially structuring the beam profile, but the realizable deviation from the Speed of Light in vacuum is small. Here we demonstrate precise and versatile control over the group velocity of a propagation-invariant optical wave packet in free space through sculpting its spatio-temporal spectrum. By jointly modulating the spatial and temporal degrees of freedom, arbitrary group velocities are unambiguously observed in free space above or below the Speed of Light in vacuum, whether in the forward direction propagating away from the source or even traveling backwards towards it.