An Ultrafast Optoelectronic THz Beam System: Applications to Time-Domain Spectroscopy
Recently, there has been a great deal of work demonstrating the generation of THz radiation (1 THz = 33.3 cm-1 = 4.1 meV) via material and electronic excitation by ultrashort laser pulses. Modern integrated circuit techniques have made possible the precise fabrication of micron-sized dipoles, which, when photoconductively driven by fsec laser pulses, can radiate well into the THz regime. An alternative and complimentary approach has been to extend radio and microwave techniques into the THz regime through the use of optoelectronic antennas. Other sources based on various physical systems and effects include the emission of an electromagnetic shock wave due to a volume dipole distribution moving faster than the phase velocity in the medium, i.e., electro-optic Cherenkov radiation, and the electromagnetic shock wave radiated by a surface-dipole distribution propagating faster than the phase velocity in the substrate.
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