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We present the effect of self-similarity in fractal photoconductive THz emitters. The performance of fractal THz PC emitters are compared to those of non-fractal emitters, and their radiation properties are studied. It is demonstrated that the THz radiation emission enhancement results from the inherent fractal self-similarity and not only from the sub-wavelength apertures pattern present on the antenna’s surface. Through the application of this concept, photoconductive THz emitters having higher THz radiation power could be designed and fabricated.

We present on the relationship between the bow-tie antenna length and its THz spectral emission response. Three well-known approaches for predicting accurate antenna length for a given central frequency were utilized and their validity was experimentally tested. It is shown that the simple quasi-static approach compare to other approximations is valid for frequencies up to ~1.5 THz. The bow-tie THz photoconcudtive (PC) emitter designed using this approximation exhibits THz radiation having the most accurate central frequency compared to the design frequency. Interestingly, the THz PC emitter utilized from this design technique also possesses the optimum radiation bandwidth.

We report the observation of terahertz (THz) electric field induced conductivity modulation in sub-wavelength gold plasmonic media. Through all-THz pump-probe time-resolved transmission spectroscopy, we demonstrate that the presence of induced surface charges influences near-field mediated light propagation. The phenomenon is ascribed to the enhanced metal conductivity due to enhanced surface density of conduction electrons. The surface induced charge dynamics are revealed via phase-dependent time-resolved signatures. The phenomenon is a prelude to a wide class of ultrafast active THz plasmonic devices and paves the way for plasmonic field effects devices, similar to semiconductor ones.

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.

A time resolved study of the THz plasmon dynamics in a random metallic ensemble is presented. This investigation is performed via a THz pump-THz probe experiment. It is illustrated that the electric field of the transmitted THz probe pulse shows an enhancement when the metallic ensemble is first excited by means of a THZ pump pulse. The effect is studied versus the temporal delay of the probe pulse with respect to the pump pulse.

New classes of photoconductive THz emitters based on Apollonian as well Sierpinski fractals and their complementary counter parts are presented. It is shown that for each fractal class the emitted THz radiation power increases as the fractal order is increased. It is shown that the self-similarity of plasmonic current present on the antenna surface results in superior performance compared to conventional bow-tie 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 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.

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 spectroscop y. 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. Keywords: Terahertz imaging, terahertz spectroscopy, plasmonics, super-resolution 1. INTRODUCTION From Hu and Nuss’ first pioneering experiments in 1995 1 , Terahertz (THz) imaging has evolved into one of the most practical applications of THz time-domain spectroscopy (THz-TDS). THz-TDS owes its continuing success to properties such as being broadband, sub-picosecond temporal resolution and phase sensitive coherent detection combined with the innate properties of a variety of dielectric materials. THz-TD S has been proven to be very successful for object and spectral imaging in a number of different fields, such as drug identification

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.

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.

We present a review on a special class of photoconductive (PC) terahertz (THz) dipole emitters based on fractal geometry. A comprehensive study of these superior THz antenna designs that are able to emit higher THz radiation power and detect lower THz radiation signal levels than the traditional THz PC antennas is performed. It is shown that the presented fractal PC THz emitters operate in a plasmonic regime. This concept is applicable to all fractal geometries such as Sierpinski and Apollonian fractals. In addition, the effect of self-similar geometry on radiation properties of fractal PC THz emitters is presented.

A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.

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.