Generation and manipulation of THz waves Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0r967621g

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  • In this thesis I studied several THz components that can be used for potential THz technology. THz waves were generated in nonlinear medium via optical rectification of femtosecond optical pulses. Utilizing the phase matching condition between the optical and THz waves in a ZnTe crystal, single-cycle broad-band THz pulses were obtained. On the other hand, a tunable narrow-band THz waves were generated in PPLN structures based on a quasi-phased matching process. THz waves were detected via free-space electro-optic detection. Several methods of THz pulse shaping were demonstrated. First, the generated THz waves replicated the polled lithium niobate (PLN) domain structures. In the 2nd method, we controlled the THz pulse shape by adjusting the delay time between two coherent optical pulses impinging on a fanned out periodically poled lithium niobate (FO-PPLN) structure. The 3rd method is an adaptive THz pulse shaping technique in which each frequency component of the THz wave generated in the FO-PPLN crystal was manipulated Controlling the ellipticity of the THz wave is highly desirable for many applications. Two linearly right-angled and delayed optical pulses incident on a nonlinear medium generated two coherent THz pulses. The ellipticity of the resultant THz wave was controlled by adjusting the delay time between the two optical pulses. The other and more efficient technique is to use the THz wave-plate consisting of a wire-grid polarizer and a mirror. The output of the waveplate is two linearly and perpendicularly polarized THz waves with a relative phase shift. The ellipticity of the output pulse is controlled by adjusting the distance between the wire-grid and the mirror located behind it. Linear THz properties of 1D periodic dielectric structure were studied. Distributed-Brag-reflectors with 5, 10, and 15 periods in both transmission and reflection arrangements were investigated. Stop-bands at (0.5-0.7) THz and (1.6-1.8) THz were shown in the transmission arrangement. High-reflectivity-bands at (0.55- 0.89) THz, (1.37-1.53) THz, and (2.03-2.29) THz in a 45° reflection geometry were observed. A resonant cavity structure was also investigated. A resonant transmission line with frequency in the center of the stop band was demonstrated.
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