Research On Stimulated Brillouin Scattering Beam Combination Laser

High-power/energy laser with a high repetition rate is widely used in several subjects, such as inertial confinement fusion, material processing and so forth. However, high thermal load and the crystal-growth volume constraint the development of higher energy solid state laser system. Therefore, the method to obtain a high-power/energy laser with a high repetition has been a focus of research recently. The beam combination is a promising method in overcoming these problems by dividing one laser beam into several beams and recombined after separate amplification.In the beam combination system, stimulated Brillouin scattering phase conjugate mirrors (SBS-PCM) are always used as reflectors because the thermal distortion in the active media could be compensated by the phase conjugate waves. However, none of these systems can overcome the limit of high load and complexity of structure. In order to obtain a reasonable high power/energy laser, a method of serial coherent laser beam combination is approached, which is based on the theory of Brillouin amplification.Firstly, a general mathematical model of SBS serial laser combination was constructed from the classic coupled-wave equation of SBS. By using of collinear Brillouin amplification model, the relationship between the parameters of system and the energy extraction efficiency of strong seed Brillouin amplification is provided. In experiment, output energy of 400 mJ and energy extraction of 85% are achieved when pump energy is 10mJ and energy of Stokes and pump beam is in the ratio of 39.5 to 1, and the conclusion that the quality of output beam is controlled by Stokes beam is drawn.Secondly, phase match in non-collinear Brillouin amplification is investigated. The reasons that cause the decrease of energy extraction efficiency are analyzed. It is indicated that mismatch of phase, which results from the crossing angle between Stokes and pump beam, is the major cause. A method of changing the Brillouin frequency shift of medium is approached to eliminate the mismatch of phase.Finally, the design of SBS serial laser beam combination system is provided, which employs a composite structure with collinear and non-collinear cells.