The electromagnetic properties of two-dimensional metallic nanostructures in the optical frequency range are studied. One example of such a structure is a periodic array of thin metallic strip pairs. The magnetic response of these structures is studied, as is the closely related emergence of the negative index of refraction propagation bands. The presence of such bands is found to critically depend on the proximity of electric and magnetic dipole resonances. It is demonstrated that the frequencies of those resonances are strongly dependent on the ratio of the structure thickness and the plasmonic skin depth. Electromagnetic structures that are much thicker than the plasmonic skin depth are shown to exhibit standard broad antenna resonances at the wavelength roughly twice the strip length. As the structures are scaled down to resonate in the visible/mid-infrared, electrostatic resonances determine the electromagnetic properties of such materials.
We demonstrate that a negative-permittivity material (silicon carbide) sandwiched between two layers of positive-permittivity material (silicon oxide) can be used for enhancement of the resolution of near-field imaging via the superlensing effect. The resulting three-layer metamaterial is also shown to exhibit an enhanced transmission when its effective dielectric permittivity matches that of the vacuum. Experimental far-field diagnostics of the superlensing based on measuring transmission coefficients through the metal-coated superlens is implemented using Fourier-transformed infrared microscopy. Superlensing is shown to be a highly resonant phenomenon manifested in a narrow frequency range.
Compact accelerators of the future will require enormous accelerating gradients that can only be generated using high power laser beams. Two novel techniques of laser particle acceleration are discussed. The first scheme is based on a solid-state accelerating structure powered by a short pulse CO2 laser. The planar structure consists of two SiC films, separated by a vacuum gap, grown on Si wafers. Particle acceleration takes place inside the gap by a surface electromagnetic wave excited at the vacuum/SiC interface. Laser coupling is accomplished through the properly designed Si grating. This structure can be inexpensively manufactured using standard microfabrication techniques and can support accelerating fields well in excess of 1 GeV m-1 without breakdown. The second scheme utilizes a laser beatwave to excite a high-amplitude plasma wave, which accelerates relativistic particles. The novel aspect of this technique is that it takes advantage of the nonlinear bi-stability of the relativistic plasma wave to drive it close to the wavebreaking.Keywords:
It is well known that circularly polarized electromagnetic waves propagating along the magnetic field in the plasma are strongly absorbed when the wave frequency matches the electron cyclotron frequency. This absorption can be eliminated by adding a weak magnetic undulator, leading to the undulator-induced transparency (UIT) of the plasma. Moreover, the group velocity of the waves in the plasma is strongly reduced, resulting in the extreme compression of the wave energy in the plasma. Compressed waves are polarized along the propagation direction and can be used for synchronous electron or ion acceleration. Numerical simulations reveal yet another interesting property of the electromagnetic waves in UIT plasma: strong coupling and conversion between two circular wave polarizations. Depending on how important this cross-polarization effect is, several propagation regimes have been identified and explored by fluid and particle-in-cell simulations.
Super-lensing is an electromagnetic phenomenon, based on the amplification of evanescent waves, capable of increasing the resolution of an optical imaging device beyond the diffraction limit. A multi-layer planar super-lens can be constructed from two materials: one with a negative dielectric permittivity ε < 0 inserted between two slabs of another material with a positive dielectric permittivity εd = −ε > 0. We numerically modelled and experimentally implemented a super-lens in the mid-infrared spectral range (around 11 μm) by creating a three-layered structure of submicron thickness, SiO2/SiC/SiO2, in which the polaritonic material SiC has a negative dielectric permittivity in the restrahlen band between the frequencies of the transverse and longitudinal optical phonons. A far-field diagnostic of super-lensing based on measuring transmission and reflection coefficients through the metal-coated super-lens has been implemented using a tunable CO2 laser.