| Terahertz wave refers to the electromagnetic radiation wave whose frequency range is from 0.1 THz to 10 THz.It plays an important role in the application fields such as nondestructive testing,imaging,communication,national defense and security,as well as the basic research fields such as physics,chemistry and life science,and so on.The application of terahertz wave and the development of terahertz technology are indispensable to excellent terahertz radiation sources.The intracavity terahertz parametric oscillator based on the Stimulated Polariton Scattering(SPS)effect is an important terahertz radiation source,it takes the advantages of compact structure,room temperature operation,easy tuning,low oscillation threshold and low cost and has become an important part of the studies for terahertz radiation sourcesSo far,the experimental research of the intracavity terahertz parametric oscillators has developed for more than ten years and made great progress.However,there are few reports on its theoretical research.In this paper,the coupled wave equations for the intracavity terahertz parametric oscillator are developed by considering the large angle non-collinear phase matching,then the rate equations model is derived and obtained,which enriches the theoretical work of the intracavity terahertz parametric oscillator.The experimental results of the intracavity Q-switched terahertz parametric oscillators based on MgO:LiNbO3 and RbTiOPO4 crystals are compared with the theoretical results,and they are basically in agreement.By using this model,some suggestions are given for optimizing the performance of the intracavity Q-switched terahertz parametric oscillators.The main research contents of this thesis are as follows1.Considering the non-collinear phase matching condition,the coupled wave equations describing the stimulated polariton scattering are derived,and the nonlinear coefficients are analyzed.By using the plane wave approximation,the physical model of the intracavity terahertz parametric oscillator is reasonably assumed,and the terahertz intensity is expressed as a function of the fundamental intensity IF,Stokes intensity Is,the gain coefficient gT,the absorption coefficient?T and the beam diameter D.Finally,the rate equations of the population inversion density and photons density with time are established to describe the change of the photons density pulse of the fundamental,Stokes and terahertz waves2.The characteristics of MgO:LiNbO3 crystal are described,and the frequency-dependent nonlinear coefficients of the coupled wave equations of MgO:LiNbO3 crystal is calculated.The terahertz tuning characteristic and power input and output relationship curves of the intracavity Q-switched terahertz parametric oscillators based on MgO:LiNbO3 crystal is given by using the rate equations,and the calculated results are basically consistent with the experimental results3.The tuning and power output characteristics of terahertz wave produced by diode-end pumped intracavity Q-switched RbTiOPO4 terahertz parametric oscillator are analyzed.The obtained tunable ranges of THz waves are 3.01 THz to 3.13 THz,3.52 THz to 4.12 THz,4.54 THz to 4.67 THz,5.38 THz to 6.08 THz and 6.90 THz to 7.10 TH,respectively.When the LD pump power is 5.8 W and the pulse repetition frequency is 8 kHz,the obtained maximum terahertz average output power is 112.5 ?W at 3.8 THz.The theoretical model is used to simulate the power and pulse characteristics at 3.8 THz,the results are in agreement with the experimental results4.A series of curves of the influence of the absorption coefficient aT,gain coefficient G and pulse repetition frequencyf on the photon density peak ?Tmax and integral value ?T-int are obtained by solving the rate equations numerically.Based on these curves,the influence of these parameters on the performance of intracavity Q-switched terahertz parametric oscillators is illustrated,and some suggestions are provided for the optimal design of the intracavity Q-switched terahertz parametric oscillators. |
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