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Suppression Of Thermal Effects And Stimulated Brillouin Scattering In High Power Fiber Lasers And Beam Shaper Of The Laser Diode Arrays

Posted on:2009-08-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:C C WangFull Text:PDF
GTID:1118360272984603Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
The rare-earth-doped single-mode fiber laser sources have attracted considerable attention recently in industrial, medical, and military application due to their outstanding advantages, such as high brightness, high efficiency, good compactness,and excellent beam quality, compared to traditional gas and solid-state lasers. Furthermore, the large surface-to-volume ratio gives them excellent capability of heat dissipation. However, scaling of the output power from the high-power fiber laser sources is limited by the stimulated Brillouin scattering and thermal effects. Under the supports of national 863 high technology program, this thesis is mainly devoted to the detailed researches on the suppression of stimulated Brillouin scattering and thermal effect in high-power fiber laser sources. And the main achievements of this thesis are listed as follows:1. The time independent rate equations were solved by relaxation menthod.A novel method based on genetic algorithm is firstly proposed to optimize distributed pump powers and the length of fiber segments in kilowatt fiber laser sources. The uniformity of temperature distribution was realized , and meanwhile the output signal power was as high as possible.2. The set of differential equations for a single core and multicore fiber amplifier with pump, signal and the first-order Stokes, taking into account effects of thermal gradients caused by heat generation, is presented. The thermal conduction equations are solved by finite element method. The influence of pump schemes, pump powers, convective coefficient, initial power of Stokes, density of the rare earth dopant and fiber length on suppression of the stimulated Brillouin scattering is studied. The stimulated Brillouin scattering gain and maximum operating temperatures are compared between single core fiber amplifier and 19-core fiber amplifier with the same optimal fiber length. Compared to the single core fiber amplifier, the 19-core fiber amplifier has lower maximum operating temperatures, which provide more space for further increasing output power.3. The mode-selection method based on a single-mode microstructured optical fiber(MOF) in the multicore fiber(MCF) lasers is presented. With an appropriate choice of the designed parameters of the MOF, the power coupling coefficient between the fundamental mode(FM) of the MOF and the in-phase mode can be much higher than those between the FM and the other supermodes. As a result, the in-phase mode has the highest power reflection on the right-hand side of the MCF laser cavity, and dominates the output laser power. Compared to the MCF lasers based on the Talbot cavity, the MCF lasers with the MOF as a mode-selection component have higher effectiveness of the in-phase mode selection.4. Gauss beam with the optimal beam waist can be the seed source of the multicore fiber amplifiers. However, the output beam quality of the mulitcore fiber amplifiers will degrade with a little shift of the beam shift. Consequently, a novel method is proposed to reduce the requirement for the high precision of the Gauss beam waist.5. The emission beam of the laser diode arrays(LDA) has an asymmetrical distribution and is astigmatic ,that is ,the waists and divergences of the beam in the fast and slow axes are different. To equalize the beam parameter products(BPP) of the asymmetrical laser beam, a new beam shaper based on the prism groups is developed and demonstrated by experiment. By focusing the reshaped beam into an optical fiber with the diameter of 650 um and numerical aperture of 0.46, high quality laser beams can be obtained and the overall efficiency is 52.6%.
Keywords/Search Tags:Fiber Laser, Fiber Amplifier, Single-Frequency, Multicore Fiber, Thermal Effect, Stimulated Brillouin Scattering, Beam shaping, Finite Element Method
PDF Full Text Request
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