| Summary: | 碩士 === 國立中山大學 === 光電工程學系研究所 === 100 === In this thesis, a novel method for multi-pulse with equal chirp characteristics and more efficient THz generation through two photon absorption (TPA) are investigated and demonstrated. These are all the first time, for our best knowledge, odd multi-pulses generation and innovative approach for efficient THz through TPA are proposed and studied.
By modulating the amplitude and phase of the spatial light modulator with the pulse shaper, the number of multi-pulses can be adjustable without the limitation of even number only. Meanwhile, the chirp properties of the generated pulses are with the same characteristics and tunable also. For the case with bandwidth of 10nm, the generated multi-pulses with equal chirps varying from -20000fs^2 to 20000fs^2 are demonstrated and the results have a good agreement with the theoretical estimation. We also discuss the number of the multi-pulses and inequalities of the amplitude of the pulses are limited by the spectral resolution of SLM within the pulse shaper.
Regarding to efficient THz radiation, it can be generated more efficiently from a low-temperature-grown GaAs (LT-GaAs) photoconductive (PC) antenna by taking into account the TPA induced photo-carrier in the photoconductor. A rate-equation-based approach using the Drude-Lorentz model taking into account the band-diagram of LT-GaAs is used for the theoretical analysis. The super-linear power dependent photocurrent clarifies the role of TPA. Previously unnoticed THz pulse features and anomalously increasing THz radiation power rather than saturation were observed. These are in good agreement with the theoretical predictions.
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