Research On Widely Continuous-tunable Mid-infrared Laser

Optical parametric oscillator (OPO) is one of the most important ways to get widelycontinuous-tunable mid-infrared lasers. The pump light could be converted into signal lightand idler light by this way. Meanwhile, it can generate widely tunable coherent light.Furthermore, the OPO possess the characteristics of high efficiency, simple structure, andhigh work stabilization and it could be made in small and all-solid. In recent years, with theinvention of the new nonlinear crystals, especially the invention of the periodically poledMgO-doped lithium niobate (MgO:PPLN) crystal, and the rapid development of thenonlinear frequency transformation and the technologies for the tunable laser, lots ofimportant breakthroughs have been made in the field of OPO. The OPO has been used inmany fields, such as CARS, laser spectroscopy, environmental monitoring, remote sensing,material handling, laser ranging, infrared interference and countermeasure. Therefore, theresearch on the OPO and its applications will become more and more important for thedevelopment of the modern science and technology. The perspective of the studies on OPOis bright.The author has done some theoretical and experimental research work onquasi-phase-matched (QPM) widely continuous-tunable mid-infrared OPO which is basedon PPLN crystal and MgO:PPLN crystal. Meanwhile, some experimental research work onoptical parametric generator (OPG) has been done, too. The main research works aresummarized as follows:(1) The worldwide research status at present and the developing trend in the future ofthe widely continuous-tunable mid-infrared OPO have been studied and investigated.Therefore, the important points and the direction of our own research work are clear.(2) The interrelated basic theories of the widely continuous-tunable mid-infrared OPOhave been analyzed and discussed. Such as the three wave interaction in the OPO or OPG,QPM theory, and the basic theory of the OPO. Furthermore, the gain, threshold value, andconversion efficiency of the OPO have been analyzed. And introduced how to design theOPO system based on PPLN and MgO:PPLN. (3) The research work of the widely continuous-tunable mid-infrared single resonantPPLN-OPO has been reported. The pump source is an acousto-optically Q-switchedNd:YAG laser. The dimension of the PPLN crystal is 50mm×10mm×0.5mm and the gratingperiods of the PPLN crystal are 26.5μm, 27.5μm, 28.5μm, 29.5μm, and 30.5μm. The idleroutput ranges of 2.80-3.17μm, 3.34-3.60μm, 3.77-3.97μm, 4.15-4.32μm, and 4.48-4.62μmare obtained by changing the temperature of the crystal from 40 to 200℃and the gratingperiods of the PPLN crystal. And the obtained maximum idler output power is 1.23W at3.09μm.(4) The research work of the widely continuous-tunable mid-infrared single resonantMgO:PPLN-OPO has been reported. The pump source is an acousto-optically Q-switchedNd:YAG laser. The dimension of the MgO:PPLN crystal is 50mm×10mm×1mm and thegrating periods of the MgO:PPLN crystal are 26.5μm, 27.5μm, 28.5μm, 29.5μm, 30.5μm,and 31.5μm. The idler output ranges of 2.83-2.89μm, 3.10-3.38μm, 3.57-3.78pμm,3.95-4.12μm, 4.28-4.46μm, and 4.65-4.79μm are obtained by changing the temperature ofthe crystal from 50 to 200℃and the grating periods of the MgO:PPLN crystal. Theobtained maximum idler output power is 2.17W at 3.33μm. And the maximum idler outputpower of the MgO:PPLN-OPO is larger than that of the PPLN-OPO.(5) The research work of the widely continuous-tunable mid-infrared single resonanttwin-MgO:PPLN cascaded OPO has been reported firstly. The pump source is anacousto-optically Q-switched Nd:YAG laser. The dimension of the two MgO:PPLNcrystals is 40mm×10mm×2mm and the grating periods of the MgO:PPLN crystal are 26μm,26.5μm, 27μm, 27.5μm, 28μm, 28.5μm, 29μm, 29.5gm, 30μm, 30.5μm, and 31μm. Theidler output range of 2.789-4.957μm is obtained by changing the temperature of the crystalsfrom 40 to 200℃and the grating periods of the two MgO:PPLN crystals. The obtainedmaximum idler output power is 2.23W at 3.344pm. And the maximum idler output powerof the twin-MgO:PPLN cascaded OPO is larger than that of the MgO:PPLN-OPO.(6) The research work of the widely continuous-tunable mid-infrared twin-MgO:PPLNcascaded OPG which based on 1.342μm pump source has been reported firstly. The pumpsource is a diode-pumped Q-switched Nd:GdVO₄ laser operated at 1.342μm. Thedimension of the two MgO:PPLN crystals is 40mm×10mm×2mm and the grating periods of the MgO:PPLN crystal are 29μm, 29.5μm, 30μm, 30.5μm,31μm, and 31.5μm. The idleroutput range of 4.144-4.851μm is obtained by changing the temperature of the crystalsfrom 40 to 200℃and the grating periods of the two MgO:PPLN crystals. The obtainedmaximum idler output power is 340m W at 4.144gm.