Reserach On The Generation Of Terahertz Wave Based On Stimulated Polarition Scattering

Terahertz?THz?technology has important research value and broad application prospects in many fields such as national defense and anti-terrorism,medical diagnosis,material properties,military communication,and atmospheric detection.The THz wave radiation generated by the nonlinear optical parameters and the optical difference frequency method has the advantages of operating at room temperature,wide tuning,high power,simple structure,and narrow line width.This thesis mainly studies the generation of THz waves based on optical difference frequency and optical parameters.The main contents are as follows:1.The effects of the coupling between the lattice vibration mode and the light wave and the effect of the polar lattice vibration mode coupling with the light wave on the crystal dispersion curve are analyzed.The three-wave interaction process in the process of stimulated polariton scattering is studied.Gain coefficient and absorption coefficient expression of THz wave is derived.2.A theoretical model of the terahertz parametric oscillator based on MgO:LiNbO₃crystal at polariton resonance region are established.A wide tuning THz wave output is achieved by changing the phase matching angle.The effective parameter gain length based on MgO:LiNbO₃ crystal under the condition of non-collinear phase matching is studied by varying the pump wavelength and radius.Gain and absorption coefficient of THz wave based on MgO:LiNbO₃ crystal at polariton resonance region are calculated.3.The wide tuning THz wave is generated by stimulated polariton scattering based on KTiOPO₄ crystal.The expression of effective parameter gain length based on KTiOPO₄crystal under non-collinear phase matching condition is derived.The gain coefficients of THz wave and Stokes wave are calculated.The calculation results show that the KTiOPO₄ crystal has a larger gain coefficient and a lower absorption coefficient than the MgO:LiNbO₃ crystal,so the KTiOPO₄ crystal is more favorable for the output of the THz wave.4.The output characteristics of THz wave based on the parametric effect of KNbO₃crystal are studied.Wide tuning THz waves can be generated by varying the pump wavelength and phase matching angle.The gain and absorption characteristics of the terahertz parametric oscillator based on KNbO₃ crystal and MgO:LiNbO₃ crystal are compared.The calculation results show that the KNbO₃ crystal is more suitable as a gain medium for the terahertz parametric oscillator.5.The phase inversion wave vector of the zinc-blende crystal is used to satisfy the phase matching process to generate the THz wave by differential frequency at polariton resonance region.The parametric gain and absorption coefficient under the low loss limit of the THz wave at polariton resonance region are calculated.The continuous tuning of the THz wave can be realized by changing the wavelength of the difference frequency wave and polarization period.