P. Maraghechi

Enhanced THz radiation emission from plasmonic complementary Sierpinski fractal emitters

We present a new class of plasmonic photoconductive THz emitters based on a complementary Sierpinski gasket fractal geometry. Due to the presence of sub-wavelength perforations on the surface of the antenna, these antennae operate in the plasmonic regime. By utilizing the unique self-similar and space filling of the tailored fractal surface and the plasmonic surface current spatial distribution, photoconductive THz emitters exhibiting superior performance (~80% increase in the emitted THz radiation power) to conventional bow-tie and Sierpinski gasket THz emitters are demonstrated. It is shown that the self-similarity of the surface plasmon current present on the antenna surface is responsible for this emission enhancement.

A plasmonic random composite with atypical refractive index

We present a material composite consisting of randomly oriented elements governed by non-resonant interactions. By exploiting near-field plasmonic interaction in a dense ensemble of subwavelength-sized dielectric and metallic particles, we reveal that the group refractive index of the composite can be increased to be larger than the effective refractive indices of constituent metallic and dielectric parent composites. These findings introduce a new class of engineered photonic materials having customizable and atypical optical constants.

Terahertz plasmonic random metamaterial

We explore the terahertz electromagnetic properties of a composite metamaterial consisting of subwavelength-sized dielectric particles with metallic inclusions. We observe group refractive index exhibits atypical which cannot be explained by conventional effective medium theory. It is shown to arise from near-field particle-plasmon coupling between the metallic particles. Moreover, we provide evidence of electron spin-dependent terahertz plasmonic transport through both ferromagnetic and ferromagnetic/nonmagnetic metamaterials.

Plasmon-assisted terahertz imaging inside metal-filled media.

We present the application of THz plasmonics in imaging dielectric objects embedded in metal-filled media. By exploiting the time domain information from the transmitted pulse, signatures of the objects were observed. To enhance the low quality images acquired through THz time domain spectroscopy, a super-resolution image processing technique was applied. It is shown that pulse arrival time and phase magnitude information compared to the integrated instantaneous power of the transmitted pulse provides more detailed images of the embedded object.

Ultrafast, all-terahertz plasmonic modulation in metals

We report on the effect of induced surface charges on the propagation of the terahertz (THz) radiation via particle plasmons. The phenomenon is attributed to a change of the surface conductivity of the metallic particles.

Plasmonic complementary fractal photoconductive emitter

A new class of photoconductive THz emitters based on a complementary Sierpinski fractal is presented. The self-similarity of plasmonic current present on the antenna surface results in superior performance compared to conventional bow-tie emitters.

Imaging via terahertz plasmons

Terahertz plasmonics application in imaging dielectrics embedded in metal-filled media is presented. Signatures of the objects were observed by exploiting the time domain information and the quality of acquired images was enhanced using image processing.

Terahertz plasmonic imaging

The application of THz plasmonics in imaging dielectric objects embedded in the metallic media is presented. Signatures of the embedded object was detected when the time domain information of the transmitted pulse was analyzed by THz time domain spectroscopy. The resolution of the acquired images was enhanced by using a super-resolution image processing technique. It is further shown that the images acquired from the pulse arrival time and phase magnitude reveal more details of the embedded object compared to the pulse power information.

Enhancement of group velocity in a random composite metamaterial

We demonstrate group velocity enhancement in a composite metamaterial consisting of ensembles of dielectric and metallic particles. This finding introduces another class of metamaterials that lack spatial order but nonetheless possess peculiar electromagnetic properties.