Normal Doppler Frequency Shift in Negative Refractive‐Index Systems

Abstract

Besides the well‐known negative refraction, a negative refractive‐index material can exhibit another two hallmark features, which are the inverse Doppler effect and backward Cherenkov radiation. The former is known as the motion‐induced frequency shift that is contrary to the normal Doppler effect, and the latter refers to the Cherenkov radiation whose cone direction is opposite to the source's motion. Here these two features are combined and the Doppler effect inside the backward Cherenkov cone is discussed. It is revealed that the Doppler effect is not always inversed but can be normal in negative refractive‐index systems. A previously un‐reported phenomenon of normal Doppler frequency shift is proposed in a regime inside the backward Cherenkov cone, when the source's velocity is two times faster than the phase velocity of light. A realistic metal–insulator–metal structure, which supports metal plasmons with an effective negative refractive index, is adopted to demonstrate the potential realization of this phenomenon.

Chiral Plasmons with Twisted Atomic Bilayers

“…We highlight that while the longitudinal spin of photons and transverse spin of plasmons have been extensively studied [45][46][47], the transverse spin of photons was only recently reported [48], and the longitudinal spin of plasmons remains elusive. The longitudinal spin of plasmons might be of paramount importance to novel types of exotic spin-orbit interactions of light [46,49,50]. Moreover, we also show that stacked atomic bilayers with rotational misalignment can in general be effectively described by a chiral metasurface.…”

“…As a unique emerging feature of chiral plasmons, we find that they possess the longitudinal spin of plasmons, besides to the common transverse spin of plasmons. The revealed longitudinal spin of plasmons may enable many other exotic spin-orbit interactions of light [45][46][47][48][49][50]. We have also directly mapped twisted atomic bilayers to the chiral metasurface, which simultaneously possesses the chiral, magnetic and electric surface conductivities.…”

Photonic and plasmonic transition radiation from graphene

“…By applying the Fourier transformation or the plane wave expansion [1,2,46,47], the current density and the related electric and magnetic fields can be expressed as,…”

Toggling Near‐Field Directionality via Polarization Control of Surface Waves

“…It enables many applications, such as nanorouters [10,11], nanopolarimeters [12], nanoscopic position sensing [13,14], near-field microscopy [1], and the development of on-chip information processing and complex quantum networks [3,[15][16][17][18][19]. In general, it is achieved through the judicious design of either asymmetric waveguide structures [20][21][22] or complex excitation sources [7,[23][24][25][26][27][28], such as the extensively-studied circularly polarized dipoles. Circular electric (magnetic) dipoles [5,25,[29][30][31] are featured with a spinning electric (magnetic) dipole moment.…”