Terahertz Optical Rectification
Free space generation of terahertz bandwidth pulsed electromagnetic radiation is a fast-growing field in the area of ultrafast electronics, photonics and optoelectronics. This dissertation presents experimental observations and a theoretical analysis of the physical mechanism underlying in the production of ultrashort pulsed electromagnetic radiation by terahertz optical rectification in electro-optic crystals. In addition to our previous observation of terahertz radiation generated by ultrafast photocarrier transport in semiconductors, we confirmed that terahertz bandwidth electromagnetic radiation can be generated via nearly degenerate difference-frequency generation in electro-optic crystals. The variation in terahertz emission with crystal orientation demonstrated that the generation of terahertz radiation via optical rectification involves a bulk second-order nonlinear process. We extensively investigated a wide range of crystals, including semiconducting, electro-optic and organic crystals. We generated the most intense terahertz optical rectification emission ever reported on the organic electro-optic crystal DAST. A unique technique based on terahertz optical rectification is developed for characterization of second-order nonlinear susceptibilities over a frequency range extending from 100 GHz to several terahertz. We also studied terahertz optical rectification from semiconducting crystals as the incident photon energy was tuned across the semiconductor optical absorption bandedge. As the incident optical excitation was tuned across the semiconductor absorption bandedge, we experimentally observed the resonant enhancement and sign reversal of the second-order nonlinear susceptibility tensor element as predicted by the single anharmonic oscillator model. In addition, a comparison between the two second -order nonlinear processes, sum-frequency generation (second harmonic generation) and difference-frequency generation (optical rectification) is presented.
- Pub Date:
- ULTRASHORT PULSE;
- Physics: Optics