Research On The Generation Technology Of Dual-Wavelength Pumped Mid-infrared Fiber Laser

The mid-infrared band of 2 μm-5 μm overlaps with the atmospheric window and covers the rotation-vibration areas of common molecules,such as greenhouse gases,water molecules,air pollutants,toxic substances,biological tissues,etc.In this spectral range,the above molecules have strong absorption,so mid-infrared spectroscopy can provide extremely sensitive chemical analysis and detection.Therefore,the mid-infrared coherent source has important applications in remote sensing and real-time spectroscopy,etc.These applications include medical diagnosis,military photoelectric countermeasures,infrared imaging,and online atmospheric quality detection.In order to effectively use the potential of the mid-infrared band,various types of mid-infrared coherent sources have been developed,including fiber lasers,quantum cascade lasers,solid-doped lasers,and optical parametric lasers.Among them,the rare-earth ions doped fiber laser has attracted extensive attention from researchers due to its good beam quality,fast heat dissipation,compact structure,easy maintenance,and wide spectrum coverage.In the visible and near-infrared bands,various types of fiber lasers have been widely used in various industries.In the near-infrared band,single-mode laser output power has achieved more than ten thousand of watts,but when the output wavelength is extended to the mid-infrared band,the output power decreases exponentially with increasing wavelength.At present,laser output of more than 4 μm has not been obtained in doped fiber,and the longest output wavelength is 3.95 μm.The main reason is the lack of high-performance,low-phonon energy,low-loss mid-infrared glass,and high-quality,high-power near-infrared pump sources;another factor that limits the increase in output power of the mid-infrared laser is the inherent energy level of certainrare earth ions.For example,some energy level structure leads to strong cross-relaxation between ions,and some ion’s lifetime of the lower level of the laser in the ion is too long,and the lifetime of the upper level of the laser is too short,which is a negative factor for the generation of laser.These two factors cause that the output power of some ion-doped lasers cannot be increased or continuous wave operation cannot be achieved.For example,Tm3+ ions cannot be improved due to strong cross-relaxation,and the 2.3 μm laser output power cannot be improved;The energy level 6H11/2 of Dy3+ ions has a short lifetime and level 6H13/2 has a long lifetime,which has a self-terminating effect and cannot achieve 4.3 μm continuous wave operation.Generation material,generation technology.In order to obtain high-power mid-infrared laser in doped optical fibers,new technologies can be developed under conditions where current material properties cannot be rapidly improved.Among them,dual-wavelength pumping technology is a feasible solution.Dual-wavelength pumping uses two beams of pump light with different wavelengths to pump the laser.It scheme can remove the self-termination effect;in principle,the output power bottleneck of the laser for some doped ions under the traditional pumping scheme is lifted.To illustrate these two advantages,this paper studies the use of dual-wavelength pumping technology to generate high-power 4.3 μm and 2.3 μm lasers in Dy:InF3 and Tm:ZBLAN fiber,respectively.This article is mainly composed of the following parts:1.Established a model in which 1.7μm and 2.3 μm semiconductor lasers pump Dy:InF3 fiber to generate 4.3 μm laser,790 nm and 1.39 μm semiconductor lasers pump Tm:ZBLAN fiber to generate high-energy 2.3 μm laser.2.Numerically studied the dependence between the output power of 4.3 μm laser,the light-to-light conversion efficiency and the pump light of 1.7 μm and 2.3 μm during continuous wave operation.The effects of fiber parameters such as fiber length,fiber loss,output mirror reflectance,and doping concentration on output power are analyzed.The output characteristics of the 4.3 μm pulsed laser when using OPO to generate 1.7 μm and 2.3 μm pulsed pump light and pump Dy:InF3 fiber are studied.3.Using the strong cross-relaxation process between Tm3+ ions,a 1.39 μm laser is used to generate a high-power 2.3 μm laser with the help of photon avalanche effect.This method can break through the output power bottleneck of the current Tn3+ ion-doped lasers that can’t get more than watts of output,and realize the output of hundreds of watts.