Delay times and detector times for optical pulses traversing plasmas and negative refractive media

TL;DR

This paper investigates the delay times of optical pulses in plasmas and negative refractive media, showing equivalence of measurement methods, exploring negative delays, and analyzing effects like the Hartman effect and reshaping delays.

Contribution

It provides a detailed analysis of pulse delay times in dispersive media with negative parameters, clarifying the roles of different delay components and their dependence on medium properties.

Findings

Total delay times for evanescent waves can be negative in infinite plasma.

In the presence of an interface, total delay times become positive outside the plasma.

For negative refractive index media, the reshaping delay for propagating waves is zero.

Abstract

We show that arrival times for electromagnetic pulses measured through the rate of absorption in an ideal impedance matched detector are equivalent to the arrival times using the average flow of optical energy as proposed by Peatross {\it et al.} [ Phys. Rev. Lett. {\bf 84}, 2370 (2000)]. We then investigate the transport of optical pulses through dispersive media with negative dielectric permittivity and negative refractive index choosing the geometry such that no resonant effects come into play. For evanescent waves, the definitions of the group delay and the reshaping delay get interchanged in comparison to propagating waves. The total delay times for the evanescent waves can be negative in an infinite plasma medium even for broad-band pulses. The total time is, however, positive for broad band pulses in the presence of an interface when the radiation is detected outside the plasma. We find evidence of the Hartman effect for pulses when the distance traversed in the plasma is much smaller than the free space pulse length. We also show that for a negative refractive index medium(NRM) with $\epsilon(\omega)$ = $\mu(\omega)$ the reshaping delay for propagating waves is identically zero. The total delay time in NRM is otherwise dominated by the reshaping delay time, and for broad band pulses in NRM the total delay time is subluminal.