Intense ultrashort TeraHertz pulses: Development and applications

Terahertz (THz) radiation is the electromagnetic radiation King in a frequency) interval from 0.1 to 30 THz which corresponds to a wavelength range from 3 mm to 10 μm. In the last couple of decades numerous works have been devoted to the generation and detection of coherent THz pulses and their various applications. Despite the efforts and achievements accomplished in the past, there is still a lack of intense ultrashort table-top sources in the THz range. In the recent years a couple of techniques have emerged in order to scale-up the strength of the THz pulses. A very promising approach consists of using asymmetrically ionized gases, where a photocurrent is formed emitting intense broadband THz pulses. This approach allows reaching the micro-joule range of energy per pulse, and electric field strengths approaching the MV/cm level. In the present dissertation, after introducing a classic example of THz time domain spectroscopy, (THz-TDS), a strong emphasis is made on the generation of intense THz pulses using femtosecond plasma strings in air. The characterization of this THz source in terms of the electric field strength, the frequency bandwidth and the beam size is presented. The possibility to optimize various parameters such as the pulse duration, the polarization and the strength of the THz pulses is demonstrated through the tailoring of the filamentation process. Finally, the applications of this intense THz source to the field of art conservation, the dynamic characterization of metamaterial samples andnonlinear THz effects are presented