Experimental Research On Generation And Detection Of The Terahertz Vortex Beam

Terahertz vortex beams have broad application prospects in the fields of communi-cation,imaging,medical treatment and so on.The premise of the real-world applications of terahertz vortex beams is the generation and defection,which can meet the actual de-mand has become the basis of the real-world applications.In this thesis,we carry out the following experimental research on the generation and detection of terahertz vortex beams:1.Generation and characterization of the terahertz radiation based on optical rectifi-cation of LiNbO₃.LiNbO₃is an excellent candidate to generate non-linear optical effect since it owns a relatively high nonlinear coefficient.However,when used for terahertz radiation generation,one may encounter the phase mismatch between the pumped laser beam?800nm?and the generated terahertz beam.To overcome this problem,we take the technique proposed by Hebling.In such a framework,the wave front of the pumped laser beam is tilted to meet the phase-match condition,which has greatly improved terahertz generation efficiency.In our experimental setup,the radiation energy and the 2D and3D patten of the generated terahertz beams are maesured by the golay cell and the tera-hertz camera respectively.The relationship is characterised between the pumped energy of laser beams and the radiation energy of terahertz near the output surface of LiNbO₃.Furthermore,terahertz radiation waveforms both in the time and frequency domain are obtained by taking the electro-optic sampling technique.2.Production of Terahertz vortex by the spiral phase plate.In this experiment,the spiral phase plate is used to modulate the phase front of terahertz radiation from optical rectification in LiNbO₃to produce terahertz vortex beams.Sector plate and small hole plate are used to characterize the numbers of toplogical charges.3.Investigation of the terahertz vortex using two-color vortex fields.Laser-induced ionization of air is a burgeoning research topics in terahertz radiation generation.Com-pared with single-color laser fileds,two-color fields can yield more powerful terahertz radiation.Pilot experiments to generate vortex terahertz beams have been performed by using vortex two-color beams.