Incoherent “Slow and Fast Light”

Abstract

We show experimentally that the effects of pulse delay and advancement usually ascribed to the "slow and fast light" under conditions of the coherent population oscillations (CPO) can be universally observed with incoherent light fields on objects with the pure-intensity nonlinearity. As a light source, we used an incandescent lamp and as objects for study, a photochromic glass and a thermochromic coating. The response of the objects to intensity modulation of the incident light reproduced in all details the commonly accepted experimental evidences of the "light with a negative group velocity" and "ultraslow light". Thus we show that observations of the pulse delay (advancement) and characteristic changes in the light intensity modulation spectrum are not enough to make conclusion about modification of the light group velocity in the medium.