Related Experiment Video
Updated: Jul 18, 2026

Direct Imaging of Laser-driven Ultrafast Molecular Rotation
Published on: February 4, 2017
Simultaneous negative phase and group velocity of light in a metamaterial
Gunnar Dolling1, Christian Enkrich, Martin Wegener
1Institut für Angewandte Physik and Deutsche Forschungsgemeinschaft-Center for Functional Nanostructures, Universität Karlsruhe (TH), Wolfgang-Gaede-Strasse 1, D-76131 Karlsruhe, Germany. gunnar.dolling@physik.uni-karlsruhe.de
Abstract:
We investigated the propagation of femtosecond laser pulses through a metamaterial that has a negative index of refraction for wavelengths around 1.5 micrometers. From the interference fringes of a Michelson interferometer with and without the sample, we directly inferred the phase time delay. From the pulse-envelope shift, we determined the group time delay. In a spectral region, phase and group velocity are negative simultaneously. This means that both the carrier wave and the pulse envelope peak of the output pulse appear at the rear side of the sample before their input pulse counterparts have entered the front side of the sample.
Related Concept Videos
Spin–Spin Coupling Constant: Overview
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Distribution of Molecular Speeds
Coulomb's Law and The Principle of Superposition
The Principle of Superposition answers the question. Yes, Coulomb's Law applies to each pair of charges, and the net force on each charge is the vector sum of the...
Propagation Speed of Electromagnetic Waves
Ampere's Law in Matter
The differential form of Ampere's law in vacuum states that the curl of the magnetic field equals the permeability times the current density. In a magnetized material, the law is modified to incorporate the free and bound current...
Speed of a Transverse Wave
One of the key properties of any wave is the wave speed. Light...

