Optimization Design And Analysis Of Thulium Doped Fiber Laser

Thulium doped fiber laser operating at2μm laser output, which is in the range ofeye-safe wavelength, has the advantages of high efficiency, good beam quality, goodheat dissipation and broad tuning range, and has recently attracted much interestowing to their numerous applications in many fields, such as medicine, biological,ultrafast optics, lidar and remote sensing. Then it has become research hotspot of fiberlaser. In addition, thulium doped fiber laser operating at2μm can be used as the pumpsource of infrared laser, achieving the longer wavelength laser output. At present, thecontinuous output power has approached the kilowatt level, but with the increasingoutput power, how to optimize fiber laser system has become the important problemof the laser overall design and the engineering development.In this paper,2μm thulium doped fiber laser has been studied both theoreticallyand experimentally. The major work can be concluded as follows:Firstly, based on the rate equations, the optimum length and the slope efficiency ofkilowatt level thulium-doped fiber laser have been theoretically studied.The effects of pump power, cross relaxation coefficient, scattering loss of signallight, reflectivity of output coupling mirror and Tm3+doping concentration of kilowattlevel thulium-doped fiber laser on the optimum length of2μm laser output have beentheoretically studied. The optimum length and the maximum output power areobtained by optimizing and analyzing the parameters of thulium doped fiber laser.The dependences of slope efficiency on cross relaxation coefficient, filling factorof pump power, reflectivity of input coupling mirror, reflectivity of output couplingmirror and Tm3+doping concentration of kilowatt level thulium doped fiber laser havebeen theoretically studied. In order to achieve the higher slope efficiency, therelations between slope efficiency and different parameter has been detailedlyanalyzed. It is recommended to optimize and analyze the laser system to obtain designcriterions of the higher slope efficiency of thulium doped fiber laser.Secondly, experimental system of ring cavity thulium doped fiber laser has beenbuilt, and the output characteristics of thulium doped fiber laser have beenexperimentally studied. Pumped by a975nm laser diode, the laser output has beenobtained with the laser central wave-length of1.99μm; the variation of the outputlaser power has been analyzed at different output coupling ratio and fiber length. Finally, derived from the heat conduction equations, the temperature distributionexpressions of2μm high power thulium doped double-clad fiber laser have beengiven. The effects of pump power, cladding radius, heat transfer coefficient of highpower thulium doped fiber laser on the temperature distribution have beentheoretically studied. It is significant to reasonably increase the heat transfer andselect the larger cladding radius and the longer fiber to decrease thermal effects ofhigh power thulium doped double-clad fiber laser.