| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 92 === Terahertz (THz)-wave’s generation and detection have gained increasing interests from fundamental and applied perspectives. Nonlinear wavelength mixing has been one of the most effective techniques to generate low-power coherent THz radiations. Recently, periodically poled lithium niobate (PPLN) has become the nonlinear-optical material of the choice, which provides the compensating wave-vector to achieve the collinear phase-matching condition.
We first report high-efficiency, collinearly phase-matched terahertz-wave parametric generation (TPG) in a 6-cm long, 780-�慆 thick PPLN waveguides pumped by a ~150 �寙/pulse actively Q-switched laser at 532-nm wavelength and by a ~60 �寙/pulse passively Q-switched Nd:YAG laser at 1064-nm wavelength. We measured 80-�慆 and 330-�慆 terahertz wavelengths from the 532-nm and 1064-nm pumped PPLN crystals with domain periods of 71.5 �慆 and 67 �慆, respectively. Due to the long gain length and the waveguide-mode confinement, sub-nJ terahertz radiation at 80-�慆 wavelength was detected by a pyrodetector with 100-�寙 pump energy at the 532-nm wavelength. Furthermore, we try to accomplish the experiment of backward terahertz-wave parametric oscillation (TPO) in a 4-cm long and 780-�慆 thick PPLN waveguides having a domain inversion period of 44-�慆 and 32-�慆 pumped by a ~250 �寙/pulse actively Q-switched laser at a 532-nm wavelength. From the observed signal output, the threshold energy of the backward oscillation was ~30 �寙. The waveguide confinement of the THz wave was confirmed by comparing the signal spectrum of 1064-nm pumped PPLN crystals with 500-�慆 and 1000-�慆 thickness.
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