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Pulse centroid velocity of the Poynting vector
Natalie A Cartwright1, Kurt E Oughstun
1College of Engineering and Mathematics, University of Vermont, Burlington, Vermont 05405, USA. ncartwri@emba.uvm.edu
Summary
The pulse centroid velocity in dispersive, absorptive materials approaches the Brillouin precursor speed with increasing distance. Near the absorption band, ultrashort pulse velocities can be superluminal or negative.
Area of Science:
- Optics and Photonics
- Materials Science
- Electromagnetism
Background:
- Understanding light pulse propagation in dielectric media is crucial for optical technologies.
- Dispersive and absorptive materials significantly alter pulse characteristics.
- The Poynting vector's centroid velocity is a key parameter for pulse dynamics.
Purpose of the Study:
- To investigate the evolution of pulse centroid velocity in dispersive, absorptive dielectric materials.
- To analyze the behavior of ultrawideband (UWB) and ultrashort (US) pulses.
- To determine the influence of propagation distance and material properties on pulse velocity.
Main Methods:
- Modeling pulse propagation using the Lorentz-Lorenz formula for refractive index.
- Employing a single-resonance Lorentz model for mean molecular polarizability.
- Analyzing the Poynting vector's centroid velocity as a function of propagation distance.
Main Results:
- Pulse centroid velocity approaches the Brillouin precursor speed at distances beyond the absorption depth.
- For short distances within the absorption band, superluminal and negative velocities are observed.
- Pulse behavior is dependent on carrier frequency relative to the material's absorption band.
Conclusions:
- The study elucidates the complex velocity dynamics of UWB/US pulses in absorptive media.
- Material absorption and propagation distance critically influence pulse velocity.
- Observed superluminal and negative velocities highlight non-intuitive pulse behaviors in specific regimes.