Terahertz Time-Domain Spectroscopy : Characterization of Nonlinear Crystals, Nanowires, 2D Gratings,Organic Liquids, and Polystyrene Particles

Abstract

Different materials including nonlinear crystals, nanowires, 2D aluminum gratings, organic liquids, and polystyrene particles are characterized using THz time-domain spectroscopy based on asynchronous optical sampling. Generated THz radiation by surface-field screening in semiconductors and optical rectification in nonlinear crystal are demonstrated in this dissertation. Significant birefringence and optical phonons are observed in the investigated nonlinear crystals. The temperature dependence of free carriers and anharmonic decay of optical phonons in LiInSe₂ is investigated using low-temperature THz time-domain spectroscopy. The complex conductivity of TiO₂ nanowires in the THz frequency region is quantitatively determined, and the influences of doping as well as post-annealing conditions on the complex conductivity are presented. Surface plasmon resonances in the THz frequency range are observed in 2D aluminum gratings fabricated on silicon substrates with dfferent lattice constants and shapes, which agree well with the theoretical interpretation. The quantitative determination of the temperature dependent refractive indices and absorption coefficients of several organic liquids in the THz frequency range are demonstrated by performing transmission THz time-domain spectroscopy measurements. The extinction cofficients of polystyrene particles in the THz frequency range are calculated.