Study On High Performance Terahertz Wave Parametric Source And Its Application

Terahertz wave(THz wave),due to its unique electromagnetic spectrum characteristics,is of great interest for various applications,such as biomedical diagnosis,communication and radar detection.From the perspective of practical applications of THz technologies,high-performance terahertz wave sources have always been one of the key technical foundations.Terahertz wave parametric source based on stimulated polariton scattering has been demonstrated as a promising THz source for its possessing the advantages of widely tunable,high energy output,compactness and room temperature operation.In this dissertation,focusing on the problems of THz output energy and continuous tuning frequency range of current THz wave parametric sources,the theoretical and experimental researches of the broadband phase-matching and high-gain pumping technologies based on stimulated polariton scattering in nonlinear crystal had been conducted.And high-performance terahertz wave parametric sources with wide tuning range and high energy were realized,which was applied to measurement of radar scattering characteristics in the terahertz wave band.The main work and innovations given as follows:1.The high-efficiency terahertz wave parametric generation and wide frequency tuning characteristics of LN crystals with different stoichiometric ratios were studied.The effects of the dispersion,absorption and Raman properties of the LN crystal on the terahertz wave tunning range and conversion efficiency were theoretically analyzed.The pump recycling technique was proposed in the experiment to further improve the THz conversion efficiency.Compared with traditional CLN crystal,the THz frequency upper limit extended from 3 THz to 4.64 THz was achieved by using the SLN crystal,and the THz output energy was increased by 2.75 times at 1.66 THz.2.The tunable dual-color terahertz wave generation based on the multiple stimulated polariton scattering was studied.The effects of pump wavelength on the phase matching and THz gain during the terahertz wave generation based on multiple stimulated polariton scattering were theoretically analyzed.A tunable dual-color terahertz wave generation was achieved by the simultaneous stimulated polariton scattering processes from multiple A1-symmetry phonon modes of KTP crystal,which was pumped by a dual-wavelength laser.The THz frequencies simultaneously tuned from 3.15 THz to11.63 THz and from 1.47 THz to 6.03 THz with some gaps.Moreover,the THz output energies for the two frequencies were independent,which means that the dual-color THz wave emission with any energy ratio can be achieved.3.The terahertz wave generation based on the coherent stimulated polariton scattering was studied.The effects of the resonance enhancement of nonlinear polarizability on the parametric generation and cascade stimulated polariton scattering during the terahertz wave generation were theoretically analyzed.An injection pulse-seeded terahertz-wave parametric generator had been demonstrated in the expriments with SLN crystal and KTi OPO₄crystal,respectively.For SLN crystal,the THz frequency tuning range from 1.04 THz to 5.15 THz was achieved,and the 3d B bandwidth was increased by 2.6 times.On the other hand,for the KTi OPO₄crystal,the continuous THz frequency tuning range from 2.96 THz to 6.48 THz was achieved,and the THz output energy was increased by 6.84 times at 3.33 THz.4.The radar cross sections of typical targets in THz frequency range was experimentally studied.The near-filed THz radar cross section measurement system with the SNR of 17 d B was bulit by a self-developed injection pulse-seeded THz wave parametric generator.The radar cross sections of typical targets at 3.3 THz and 5.0 THz were obtained.Compared with the RCS at 3.3 THz,the RCS at 5.0 THz was improved by 3-7 d Bsm.