We show that electron-THz radiation can be enhanced using an extremy confined mode that we call epsilon near zero (ENZ) mode. We demonstrate a 45% absorption of a normally incident 8.74 THz wave in the volume of a single quantum well with thickness 22 nm. We also demonstrate electrical modulation of this absorption.

The electromagnetic modes of a GaAs quantum well between two AlGaAs barriers are studied. At the longitudinal optical phonon frequency, the system supports a phonon polariton mode confined in the thickness of the quantum well that we call epsilon-near-zero mode. This epsilon-near-zero mode can be resonantly excited through a grating resulting in a very large absorption localized in the single quantum well. We show that the reflectivity can be modulated by applying a voltage. This paves the way to a new class of active optoelectronic devices working in the midinfrared and far infrared at ambient temperature.

It has been predicted theoretically and demonstrated experimentally that a planar slab supporting surface plasmons or surface phonon polaritons can behave as a super lens. However, the resolution is limited by the losses of the slab. In this Letter, we point out that the resolution limit imposed by losses can be overcome by using time-dependent illumination.

We introduce a quantization scheme that can be applied to surface waves propagating along a plane interface. An important result is the derivation of the energy of the surface wave for dispersive nonlossy media without invoking any specific model for the dielectric constant. Working in Coulomb's gauge, we use a modal representation of the fields. Each mode can be associated with a quantum harmonic oscillator. We have applied the formalism to derive quantum mechanically the spontaneous emission rate of surface plasmon by a two-level system. The result is in very good agreement with Green's tensor approach in the nonlossy case. Green's approach allows also to account for losses, so that the limitations of a quantum approach of surface plasmons are clearly defined. Finally, the issue of stimulated versus spontaneous emission has been addressed. Because of the increasing density of states near the asymptote of the dispersion relation, it is quantitatively shown that the stimulated emission probability is too small to obtain gain in this frequency region.

We present an explicit form of the surface plasmon propagator. Its form has the structure of a vectorial Huygens-Fresnel principle. The propagator appears to be a powerful tool to deal with diffraction, interference and focusing of surface plasmons. In contrast with the scalar approximation used so far, the vectorial propagator accounts for near-field and polarization effects. We illustrate the potential of the propagator by studying diffraction of surface plasmons by a slit and focusing of surface plasmons by a Fresnel lens.

Surface plasmons are usually described as surface waves with either a complex wavevector or a complex frequency. When discussing their merits in terms of field confinment or enhancement of the local density of states, controversies regularly arise as the results depend on the choice of a complex wavevector or a complex frequency. In particular, the shape of the dispersion curves depends on this choice. When discussing diffraction of surface plasmon a scalar approximation is often used. In this work, we derive two equivalent vectorial representations of a surface plasmon field using an expansion over surface waves with either a complex wavevector or a complex frequency. These representations can be used to account for propagation and diffraction of surface waves. They can also be used to discuss the issue of field confinment and local density of states as they have a non-ambiguous relation with the two dispersion relations.

The surface phonon polaritons (SPP) excitation by hot electrons of an appropriate two-dimensional gas could make possible to implement an opto-electronic device emitting around 10 THz. To quantitatively assess the SPP emission by inter-subband electron relaxation in a GaAs/AlGaAs quantum well, accurate electron/SPP scattering rates have been included in a particle Multi-Subband Monte Carlo (MSMC) simulator. Our results suggest some possible optimizations to enhance the SPP emission in order to design new Tera-Hertz sources.

We focus on the surface plasmon-polaritons (SPP) propagating along flat surfaces. Their propagation is often described in terms of a mode exp(i(K.r+γz-ωt)) a surface wave characterized by a frequency ω and a wavevector K parallel to the surface, decaying exponentially in the perpendicular direction. When losses in the materials is taken into account, K and ω can no longer be both real. Absorption can be described using a complex ω or a complex wavevector K. Here we derive two decompositions for the field of surface plasmons to describe their propagation, that can be used to discuss a few issues concerning SPP. We then deal with a quantum treatment of SPP, which can be used to describe the interaction of a system close to an interface and the surface plasmons of this interface.