Study On Key Techniques Of Ultrafast Coherent Terahertz Wave Generation And Detection

Terahertz (THz) radiation lies between the microwave and infrared frequenciesof the electromagnetic spectra. It has been a long progress since the discovery of theterahertz gap. Thanks to the development of ultrafast laser and low-dimensionalsemiconductor technologies, there generated a series of terahertz sources anddetectors with high sensitivity and performance, which greatly promoted the rapiddevelopment of terahertz science and technology. With a further research of terahertzradiation, there have been found quite a lot of unique properties in thiselectromagnetic band, such as its non-ionizing, less Rayleigh scattering than nearinfrared radiation, transparent to many visually opaque materials, highly sensitive towater. The features of terahertz radiation have expanded its utilization to many fields,such as identification of tumour and drugs, and so on.During the development of terahertz techniques, high attention has been paid toterahertz sources and detectors. How to efficiently generate and detect terahertzsignals is quite important to further research and application of terahertz technology.In this thesis, some generation and detection methods of terahertz signal have beeninvestigated. The detailed contents are shown as follows:（1） Terahertz generation based on a home–made photoconductive antenna wasinvestigated. For a further understanding of terahertz generation mechanism,the influences of an injured photoconductive antenna and the spot size of theincident laser on the antenna surface were discussed. Through optimizingparameters of the system, we have increased the time-domain signalamplitude by50%, and expanded the frequency coverage from2THz up to4THz.（2） Terahertz generation from laser-induced air plasma was investigated. Byusing different mechanism happened in laser-induced air plasma, such asponderomotive force, external biased field and four-wave-mixing, terahertzradiation have been achieved effectively.（3） Two detection methods using electro-optic crystal and photoconductiveantenna were compared. The ultrafast coherent terahertz signal was detectedsuccessfully by the home-made photoconductive antenna.