| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 94 === This dissertation demonstrates for the first time a ~10 GHz linewidth optical parametric oscillator at THz frequencies using an over-moded lithium niobate waveguide. We first utilized the Littman configuration to demonstrate a narrow line width seeding laser which bandwidth is about 350 MHz and the tuning range 0.42 nm of the central wavelength. Then, we demonstrated high-gain, high-efficiency terahertz parametric oscillator (TPO) and grazing incidence terahertz parametric oscillator (GITPO) in a z-cut LiNbO3 slab waveguide. With 4.6-mJ pump energy at 1064 nm wavelength, the signal conversion efficiency of TPO and GITPO were 10.6% and 4.7%, respectively, in a 1-mm-thick, 45-mm-long z-cut LiNbO3 THz slab waveguide. Furthermore, we also demonstrated a waveguide parametric oscillator with an ultra-low threshold intensity of 70 MW/cm2. The grazing incidence terahertz parametric oscillator was also achieved by using an intra-cavity grazing-incidence grating and a 1064-nm high reflector to form an output coupler. Moreover, we injected CW 350-MHz line-width laser as a seeding laser to narrow down the line width of the pumping laser. After seeding the pump laser, the bandwidth of the signal wave was also narrowed from 235 GHz to 13 GHz. In addition, we can change the Δz to fine tune the center wavelength of the signal, when we tune the 0.12mm we can obtain the 0.1-nm shift and we either can obtain the 0.5-nm tuning range by adjusting the HR mirror of GIPTO setup. Finally we utilized a wire mesh etalon to measure the THz wavelength around 166μm. The bandwidth of the THz output is expect to be less than the sum of the pumping and signal bandwidth.
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