2μm Tm³⁺-Doped Fiber Laser

It's a milestone in the development of fiber laser that the invention of the technology of cladding-pump. Maintaining the advantage of high efficiency, high beam quality, good reliability, compact configuration and great cooling ability, the capacity of output power of fiber laser begins to step up from milliwatts and watts to hectowatts even kilowatts, which has greatly extended the application area of fiber laser. The Tm³⁺-doped silica fiber pumped by the LD operating at 800nm obtains the laser transition between ³F₄ and 3H6 at approximately 2μm. The cross-relaxation process of ³H₄ , ³H₆â†'³F₄ ,³F₄ between Tm³⁺ energy levels provides a quantum efficiency nearly 2, thus a high efficiency source at 2μm could be obtained. The laser near 2μm that operates at a eye-safe spectral region has a promising application in LIDAR, remote sensing, medicine, and the pump source of 3⁵μm OPO as well. Therefore there is great value in researching Tm³⁺-doped silica fiber laser operating at 2μm.The research of this paper is to obtain laser output at 2μm in Tm ³⁺-doped fiber laser which is cladding-pumped by LD and its output characteristics. The output characteristics of Tm³⁺-doped silica fiber laser is researched and analyzed from theory and experiments. Based on the theoretical model of fiber laser under strong pump condition, the threshold pump power and the output power have been analyzed under single and double pump conditions. The lasing transition between the energy levels of Tm³⁺ at different pump wavelength has been analyzed theoretically, and the rate equations of Tm³⁺-doped silica fiber laser are given. The key techniques of fiber end preparation and high efficient pump coupling have been commanded in the experiments. With reasonable design on the parameters of LD, collimation-focus coupler and fiber, the experiment setting of Tm³⁺-doped silica fiber laser has been built. The measurement of fiber coupling efficiency and the fiber absorption coefficient is designed. Efficiency up to 51% of laser output in 2μm spectral region has been obtained by using Fenghuo fiber in F-P cavity and the effects on the laser wavelength shift by changing fiber length, temperature and pump means have been researched. The laser beam width has been measured by knife-edge method, and M2 factor has been calculated. At last the beam quality, slope efficiency and threshold pump power have been compared and analyzed at different fiber curvature diameter.