An Investigation On Terahertz Responses Of Semiconductors And Artificial Periodic Structures In Terahertz Region

Terahertz(THz) technology has been widely used in medical photography, medical imaging and quality control. Nowadays, one c hallenge for THz application is the miniaturization of functional device of THz generation, detection and modulation. The context of this thesis is consisted of two sections:1) THz response in electro-optical crystals excited at 1.03 μm wavelength,2) THz response of artificial periodic structures.In the first section, the feasibility of THz generation and detection us ing electro-optical crystals excited at 1.03 μm wavelength is investigated. For inorganic electro-optical crystals, it is found that the optimal emission frequency of Cd Te is at 2.65 THz; however, it reaches 4.77 THz of Ga P and 6.56 THz of Ga As, when the thickness of crystal is 0.1 mm. The response range is limited by the coherence length. The cut-off frequency of Cd Te is only 3.45 THz, while Ga P a nd Ga As with same thickness achieve 6.37 THz and 7.15 THz correspondingly. The THz response sensitivity of above crystals including the effect of intrinsic absorption are investigated, it is found that the sensitivity of Cd Te is better than Ga P and Ga As when the thickness of crystal below 1.58 mm. When the thickness exceeds this value, the THz response sensitivity of Ga As exceeds the Cd Te and Ga P. Meanwhile, for the organic crystal DAST, it achieves 12 THz bandwidth, much larger than inorganic electro-optical crystals. Therefore, DAST crystal is proposed to be an efficient THz emitter adapt for Yttrium-doped femtosecond pulse lasers.In the second section, the feasibility of THz modulation based on several artificially periodic arrays are investigated experimentally and theoretically. For the complementary split-ring resonator arrays on the flexible substrate, a distinct single-peak resonance is observed due to the inductive-capacitive(LC) resonance when the THz electrical field is perpendicular to the gap. However, when the THz electrical field is parallel to the gap, a periodic multiple resonances phenomenon is observed. With the help of electric density distribution and surface current analysis, the origin of the frequency resonance is revealed. An asymmetric Fabry-Pérot effect is found to induce the periodic resonances. For the T-type arrays on the Ga As substrate, the resonance can be modulated by changing the position of transverse axis. With the help of electric density distribution and surface current a nalysis, the results demonstrate changing the position of transverse axis cause the symmetry breaking of the energy distribution, which results in the shift of THz resonance frequency.