Research On Mode Characteristics Of Stimulated Brillouin Amplification With Fundamental Mode Induction In Large Core Fiber

The effect of beam cleanup in large core multimode fiber occurred throughStimulated Brillouin amplification, has important implications for improving the qualityof the output beam in high power fiber laser field. Mode characteristics of StimulatedBrillouin amplification in multimode fiber is discussed in the following. Theoretical andexperimental studies are carried out. Physical model has been established, for describingthe mode characteristics of Stimulated Brillouin amplification in multimode fiber.Mechanism of beam cleanup is explained before comprehensive analysis anddescription of this effect.In theory, the overlap integral, which can explain the physical origin of modecharacteristics in the process of amplification, is established by combining the specialmode characteristics of multimode fiber and the traditional physical model ofStimulated Brillouin amplification. In the experiments, program is designed forstudying the Stimulated Brillouin amplification with fundamental mode induction in GImultimode fiber which has several kinds of core diameter. After getting the keytechnologies of experiment, such as select mode excitation, control of the optical path,image acquisition and so on, beam cleanup with high efficiency is achieved inmultimode fiber with62.5μm,105μm and200μm core diameter. Especially, an iconicresult is obtained in GI multimode fiber with105μm core diameter, that the M2factor ofoutput beam is improved to1.5through the effect of Stimulated Brillouin amplificationwith fundamental mode induction. Then a physical model is established after combiningthe theory and experiment, which can explain the relationship between beam cleanupthrough Stimulated Brillouin Scattering and that through Stimulated Brillouinamplification in multimode fiber. Correspondingly, the concept of spontaneous beamcleanup and induced beam cleanup is defined.