Study Of Tunable Mid-Infrared And Far-Infrared Sources

Tunable mid-infrared and THz sources play a key role in wide applications,in-cluding national defense,biomedical research,substance identification and molecular analysis.Nonlinear optics(NLO)methods are proven approaches to obtain tunable mid-infrared and THz waves,due to the advantages of wide tunability,high-energy out-put,room-temperature and compact structure.It is essential to develop new crystals to replace the tradition crystals ultilized in current NLO lasers.And the performance of the mid-infrared and THz sources based on the traditional crystals can be improved significantly by studying the efficient nonlinear optics progress.Based on the nonlinear optics theory,the proper phase-matching condition and nonlinear dynamic process in the newly developed NLO crystals,including BaGa₄Se₇ crystal and organic crystals,are studied theoretically to extend the tuning range and improve the conversation effi-ciency.Furthormore,the tunable mid-infrared and THz sources based on the new crys-tals are experimentally realized by optimizing the parameters of pump,phase matching condition and tuning method.In this dissertation,the main work and innovations are shown as follows:1.Mid-infrared sources based on BaGa₄Se₇ crystal with phase-matching angle-tuning method are theoretically and experimentally studied.High-energy and tunable mid-infrared sources based on BaGa₄Se₇ crystal are demonstrated by single-pass dif-ference-frequency generation(DFG)and optical parametric oscillator(OPO).The pump parameters and cavity structure are theoretically and experimentally studied in DFG and OPO to improve the performances of the mid-infrared sources.Based on the DFG method,maximum pulse energy of 5.72 m J at 3.58?m is obtained at the dual-wavelength pump energy of 58.4 m J/pulse.The wavelength tuning range is 3.36-4.27?m with a flat tunability.And widely tunable mid-infrared BaGa₄Se₇-OPO with high conversion efficiency are also experimentally demonstrated in double-pass configura-tion.The tuning range are 3.9-5.1?m and 8-14?m,respectively.Furthermore,the high-energy output of 1.05m J/pulse at 11?m is obtained.2.To avoid the Fresnel reflection and beam-cutting effect in the mid-infrared sources with angle-tuning method,a combined tuning method is developed in the tun-able mid-infrared tandem BaGa₄Se₇-OPO.The tandem BaGa₄Se₇-OPO was intracavity-pumped by the tunable signal wave at¹?m generated from a KTi OPO₄-OPO(KTP-OPO)in doubly-resonant oscillator(DRO)configuration,is demonstrated.A tuning range of 4.1-4.5?m is obtained with just 5 individual phase matching angles of the BaGa₄Se₇ crystal.The maximum output energy of 1.92 m J/pulse is obtained at 4.26?m.3.The high-energy and ultra-wideband tunable THz sources based on DAST crys-tal,via DFG and relative applications are studied.With the outstanding NLO character-istics of DAST crystal,the 0-tpye phase-matching condition and the optimum pump parameters are theoretically studied in the ultra-wideband THz frequency range.Pumped by the dual-wavelength KTP-OPO,high-energy and broadly tunable mono-chromatic THz sources based on DAST crystal is experimentally achieved.The ultra-wideband tuning range of 0.1–20 THz and the highest output energy of??J/pulse are obtained.And the ultra-wideband spectroscopies of solid,liquid,plasma and biomedi-cal tissue are measured with the ultra-wideband tunable THz source.4.The ultra-wideband tunable THz sources based on new organic crystals via DFG are studied.To avoid the tuning characteristic of DAST crystal,four different kinds of organic crystals,including DSTMS,OH1,HDB-T and OHI-T,are ultilized and studied to generate ultra-wideband tunable THz wave.Furthermore,the tuning characteristics and advantages of each crystal are compared and analyzed in theory and experiment.