Transparent anomalous dispersion and superluminal light-pulse propagation at a negative group velocity

Abstract

Anomalous dispersion cannot occur in a transparent passive medium where electromagnetic radiation is being absorbed at all frequencies, as pointed out by Landau and Lifshitz. Here we show, both theoretically and experimentally, that transparent linear anomalous dispersion can occur when a gain doublet is present. Therefore, a superluminal light pulse propagation can be observed even at a negative group velocity through a transparent medium with almost no pulse distortion. Consequently, a negative transit time is experimentally observed resulting in the peak of the incident light pulse to exit the medium even before entering it. This counterintuitive effect is a direct result of the rephasing process owing to the wave nature of light and is not at odds with either causality or Einstein's theory of special relativity.

On Impulse Distortion in Dispersive Media

“…[1][2][3]. Besides superluminality also counterintuitive negative pulse transit times were experimentally confirmed.…”

Superluminal two-color light in a multiple Raman gain medium

“…Among the most exciting is a propagation in the backward direction (backward light) or the appearance of a pulse peak at the exit of the medium prior to entering (negative transit time) [14,19]. Recent experimental observations confirmed both of these predictions [19,20].…”

Neutralization of LC- and RC-Disturbances with Left-Handed and NGD Effects

“…The first experimental verification of this NGV phenomenon was performed in 1982, by Chu and Wong by using laser pulses propagating a GaP:N sample as shown in [8]. To verify the existence and illustrate the significance of this extraordinary phenomenon, many theoretical and experimental demonstrations were performed [8][9][10][11][12][13][14][15][16]. This counterintuitive phenomenon was explained from the pulse reshaping because of constructive and destructive interferences in the frequency band of anomalous dispersion.…”

“…This counterintuitive phenomenon was explained from the pulse reshaping because of constructive and destructive interferences in the frequency band of anomalous dispersion. In this region, it was shown several times, that the group refractive index ) (ω g n can become negative [12][13][14][15][16][17][18]. In this case, the group velocity, which is defined as:…”

“…This extraordinary physical concept was, first, proposed by Veselago in 1968 [27] and then, experimented in the early 2000s by Pendry and Smith [28][29][30][31]. Several experiments confirmed the physical existence of the superluminal and NGD phenomena with negative refractive index media [32][33][34][35][36][37]. In the presence of losses, the NGD generated by NGD passive media is accompanied by excessive losses [15][16][38][39][40].…”