The Study of Terahertz Radiation Mechanism from Photoconductive Antenna by Femtosecond Pulse Shaping Technology
| Autor: | Sung-Hui Lin, 林松輝 |
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| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 In this thesis, role of chirp properties within mode locked pulses to generate efficiency and broadband THz radiation is investigated. By integration of pulse shaping technique and pump-probe measurement, behavior of increasing carrier relaxation time with chirp and positive sign is observed and explained by frequency dependent excess energy. Meanwhile, chirp- and power- dependence of THz radiation are studied using chirp controlled PC antenna based THz radiation system. We confirm the nature of asymmetry and positive preference of THz radiation for mode locked chirp pulse. We further observe an anomalous and nonlinear increase of THz radiation with increasing power of transform-limited and tight focusing exciting pulse. This could be due to distribution of carries from two photon absorption and is the first experimental report of two photon absorption induced THz radiation enhancement which have been predicted theoretically. In addition, we analyze phenomenon observed by Drude-Lorentz model with obtained chirp- and power- dependent carrier lifetime and influence of chirp within sampling. Finally, we suggest possible approaches for generating high efficiency and broadband THz radiation：(1) positive chirp exciting can enhance radiation power but depress the high frequency part. (2) transform-limited exciting pulse can provide broader spectrum and further enhance power under highly tight focusing condition due to TPA contribution. (3) antenna with short carrier and momentum lifetime exciting by transform-limited pulse to decrease influence of PC sampling. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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