Generation of terahertz radiation by coherenct multiple-stage of optical rectification in GaSe crystals

• Main Authors: Yu-Shian Lin, 林育賢
• Other Authors: Ci-Ling Pan
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/33907118148208132742

碩士 === 國立交通大學 === 光電工程系所 === 96 === In this thesis, we successfully construct a theoretical model to interpret the optical rectification process in nonlinear optics. Generation of terahertz radiation via frequencies mixing in GaSe crystal by use of the ultra-fast pulses laser is theoretically simulated by taking into account of the phase-matching parameter and absorption coefficient of nonlinear optical crystal. The frequency spectra and time-domain waveforms of terahertz radiation deduced from the numerical simulation are verified by the experimental results. Furthermore, this theoretical model can be extended to the application of coherent multi-stage optical rectification technique. We experimentally generated terahertz radiation via multi-stage optical rectification process. By accurately adjusting the time delay between the two terahertz radiation from the two stages, the terahertz radiation can be coherently superposed with higher output power. This technique verifies the great potential of spectral synthesis of terahertz radiation. Moreover, it is observed that the coherence between the two terahertz radiation from the two stages is as high as 0.8~0.95 by the analysis of spectral-interfeometry method. Besides, the nonlinear absorption coefficient cross-section of GaSe crystal at terahertz frequencies is experimentally fitted in the range of (1.3－5.9)×10-17 cm2. Multi-stage optical rectification technique is expected to overcome the interaction length inside the nonlinear crystal, which is usually limited by group velocity mismatching. The high power terahertz radiation can be generated by coherently cascaded optical rectification processes in GaSe crystals. Under the numerical optimization, the single-cycle terahertz radiation can be generated with pulse energy as high as 400.8 nJ by use of the multi-stage optical rectification technique.