Research On Output Characteristics Of High Power2μm Tm³⁺ Doped Fiber Laser

Laser diode （LD） pumped high power double-clad fiber laser develops very fast in recentyears for its advantages such as high reliability, good heat dissipation, low threshold, highgain，compact configuration and so on. The laser near2μm that operates at eye-safe spectralregion has a promising application in laser detection and ranging, remote sensing, industrialprocessing, medicine and many other fields. There is great value in researching on high power2μm Tm³⁺doped double-clad fiber laser which has drew high attention from researchers allover the world.Thermal effects induced by fiber laser under high-power operation seriously influencethe output power, spectral linewidth, central frequency and polarization of laser, and thusresulting in a limited application of high power2μm double-clad Tm³⁺doped fiber laser. Upto now, there is no report of theoretical research considering the influence of thermal effectson output characteristics of high power2μm Tm³⁺doped fiber laser. It is therefore necessaryto investigate the thermal effects in high power2μm Tm³⁺doped double-clad fiber lasertheoretically.By establishing and numerically calculating theoretical mode based on the rate equationsand power propagation equations, we investigate output characteristics of2μm Tm³⁺dopeddouble-clad fiber laser. First, the distribution of pump power and laser power is studied, andthe influences of pump mode upon this distribution are discussed. The dependence of theoutput characteristics on parameters, such as fiber length, mirror reflectivity and overlappingfactors of pump and signal powers is investigated. According to the heat conduction equation,the expression about the distribution of temperature in high power2μm Tm³⁺dopeddouble-clad fiber laser is derived. The axial, radial and3-Dimensional temperaturedistributions are numerically simulated.To research on output characteristics of high power2μm Tm³⁺doped double-clad fiberlaser with thermal effects, the theoretical mode based on rate equations, power propagationequations and heat conduction equations is established and numerically calculated for the firsttime. According to multiphonon relaxation theory, non-radiative transition rate， crossrelaxation coefficient and energy transfer upconversion coefficient depend upon mean number of phonons. The influences of thermal effects upon mean number of phonons, absorptioncross section, emission cross section and branching ratios on output characteristics arediscussed in this paper. Finally, influences of inner clad radius, convective coefficient andtemperature upon output characteristics of high power2μm Tm³⁺doped double-clad fiberlaser are investigated. The output characteristics of silica fiber laser and ZBLAN fiber laserare compared.