On Two Models of the Light Pulse Delay in a Saturable Absorber

TL;DR

This paper compares two models explaining light pulse delay in saturable absorbers, concluding that the simpler absorption distortion model suffices and that the 'slow light' effect lacks experimental confirmation.

Contribution

It demonstrates that all experimental data can be explained by the simple model, challenging the necessity of the 'slow light' explanation based on coherent population oscillations.

Findings

The simple absorption distortion model explains all observed delays.

The 'slow light' effect has no experimental confirmation.

Claims of 'slow light' based on group velocity reduction are unfounded.

Abstract

A comparative analysis of two approaches to description of the light modulation pulse delay in a saturable absorber is presented. According to the simplest model, the delay of the optical pulse is a result of distortion of its shape due to absorption self-modulation in the nonlinear medium. The second model of the effect, proposed at the beginning of our century, connects the pulse delay with the so-called "slow light" resulting from the group velocity reduction under conditions of the coherent population oscillations. It is shown that all the known experimental data on the light pulse delay in saturable absorbers can be comprehensively described in the framework of the simplest model of saturable absorber and do not require invoking the effect of coherent population oscillations with spectral hole-burning and anomalous modifications of the light group velocity. It is concluded that the effect of group velocity reduction under conditions of coherent population oscillations has not received so far any experimental confirmation, and the assertions about real observation of the "slow light" based on this mechanism are groundless.