Superlight inverse Doppler effect

TL;DR

This paper predicts a new superlight inverse Doppler effect inside the Cherenkov cone, occurring when source velocity exceeds twice the phase velocity of light, challenging long-held tenets about light's Doppler shifts in homogeneous positive index media.

Contribution

It introduces the superlight inverse Doppler effect, a novel phenomenon where inverse Doppler shift occurs at superluminal source speeds, expanding understanding of light-matter interactions.

Findings

Inverse Doppler shift appears when v > 2v_p.

Superlight inverse Doppler effect can be spatially separated using squeezed polaritons.

Theoretical prediction facilitates potential experimental observation.

Abstract

There is a century-old tenet [1, 2] that the inverse Doppler frequency shift of light [3-13] is impossible in homogeneous systems with a positive refractive index. Here we break this long-held tenet by predicting a new kind of Doppler effect of light inside the Cherenkov cone. Ever since the classic work of Ginzburg and Frank, it has been known that a superlight (i.e., superluminal) normal Doppler effect [14-18] appears inside the Cherenkov cone when the velocity of the source v is larger than the phase velocity of light v_p. By further developing their theory we discover that an inverse Doppler frequency shift will arise when v>2v_p. We denote this as the superlight inverse Doppler effect. Moreover, we show that the superlight inverse Doppler effect can be spatially separated from the other Doppler effects by using highly squeezed polaritons (such as graphene plasmons), which may facilitate the experimental observation.