Slow light by means of coherent population oscillations: laser linewidth effects

Giovanni Piredda,Robert W Boyd

doi:10.2971/jeos.2007.07004

Abstract

Several groups have recently reported the observation of slow light propagation speeds based on the process of coherent population oscillations (CPO) under conditions such that the laser line width exceeds the width of the CPO transparency window. We explain this apparently paradoxical result by noting that the CPO effect is sensitive only to intensity variations of the incident laser field that occur on time scales comparable to or shorter than the population relaxation time of the material medium. Laser linewidths are associated primarily with phase fluctuations or with intensity fluctuations on much shorter time scales.

Highlights

There has recently been a flurry of interest in slow– and fast– light methods, inspired both by the conceptual intrigue of the possibility of exercising great control over the propagation velocity of pulses through material systems [1] and by the potential applications of these techniques in the fields of photonics and optical switching
Extreme values of pulse velocities (v c, and v negative) have been reported [2]–[4]. Work in this field made use of the properties of ultra– cold and hot atomic gases [2, 3, 5], more recently interest has turned to room–temperature solid–state systems, which in many ways are better suited for use in practical applications
We analyze some specific aspects of slow light by means of coherent population oscillations (CPO)

Summary

Introduction

There has recently been a flurry of interest in slow– and fast– light methods, inspired both by the conceptual intrigue of the possibility of exercising great control over the propagation velocity of pulses through material systems [1] and by the potential applications of these techniques in the fields of photonics and optical switching. If an intense pump field and a detuned signal field simultaneous illuminate a saturable optical material, the ground state population will be decreased as a consequence of saturation effects This decrease will consist of both a steady state depletion that depends on the average intensity of the applied fields and a time varying contribution that corresponds to the beat frequency between the pump and signal fields. This time varying contribution, that is, the coherent population oscillations, leads to decreased attenuation of the signal field, for reasons that are described mathematically by means of the calculation given below. We present an alternative description of slow light effects based on a time domain description that in some ways complements the frequency–domain description

MATHEMATICAL MODEL

SUMMARY AND CONCLUSIONS