Research On Beam Quality Active Control Technology Of High Energy Solid Slab Laser

The technical research and application about the high energy solid state laser systems witch based on the solid state slab MOPA structures become hotter with the development of the bumping, cooling and the production of the slab gain material. Since the power of single chain is limited by the gain material and the pumping efficiency, beam combination based on sub-MOPA chain is the most common method to achieve high power or energy in the solid state laser field. Now, the beam quality controlling of the sub-beam and the combinational beam is a big problem in the whole field.This dissertation mainly focuses on the technical and experimental research of the beam quality active controlling of the high energy solid state slab MOPA laser system.Since the beam quality of the single chain affect the combined beam very deeply, the paper focus on the wave-front characteristic, wave-front measurement and analysis, phase conjugated correcting method of the single MOPA chain. Some new technical proposes about the wave-front sensing and correcting to the phase aberration of the solid state slab lasers have been tested by simulations and experiments.Different from other type lasers, there are lots of local high slope and obviously rumply distributions located in the solid state slab laser beam. To improve the precision of the measuring and correcting of the wave-front aberration, the propagation of the laser beam in the HS wave-front sensor are studied with physical optical method. The micro-lens array (MLA) is modeled to simulate the relationship between the spatial frequency of the MLA and the model aberrations expressing with Legendre polynomials. To get higher spatial resolving power and phase reconstructing efficiency, a phase retrieval method based on the FFT is studied to improve the sub-aperture number of the HS-WFS. With these methods, the properties of the solid state slab laser have been measured and analyzed, and results show that most component of the phase aberrations locating below 10Hz in the time frequency domain, at the same time, there are some rumply waves locating in the long side of the beam cross section of the slab lasers.The relationship between the spatial characteristic of the aberration of the sub beams and the final beam quality of the combined beam is studied with a beam propagation simulating software. To let the far field beam quality factor less than 5, the beam quality of the sub-beams must less than 3 after the adaptive optical system correcting, further more, the peak-valley value must less than 0.5A, the RMS value no more than 0.1A, and the phase error which order less than (6,6) expressed with Legendre polynomials must be corrected over. The results instruct the phase correcting of the solid state slab MOPA chain directly.A new method name off-line calibrating and in-line positing is proposed and studied with simulations and experiments. All the results show that the new method can not only improve the efficiency but also the precision of the adaptive optical system influence function comparing with the traditional system calibrating processing.The one-dimension deformable mirror is invented and used to correct the special phase aberration of the solid state slab laser beam. To cooperate with the tow-dimension deformable mirror better, both the serial working mode and the syncretic mode are studied, the results of the experiments prove the capability of the one-dimension deformable mirror, with the one-dimension deformable mirror, the driving voltage of the two-dimension DM become very reasonable and safety to get excellent correcting efficiency of the high order phase aberrations.A wave-front over sampling method is proposed and studied to deal with the high spatial frequency component of the wave-front of the solid state slab laser beam. The best matching of the sub-aperture number and the actuator is optimized with the decreasing of the conditional number of the AO system. Setting the slope of the invalid sub-aperture as zero and reshaping the influence function dynamically are used to overcome the absent apertures, the results of the simulations and experiments both prove the correctness and availability.Finally, this paper constructs lots of experiments to prove the methods mentioned above in the wave-front measuring and analyzing and phase correcting with different MOPA single chains. With the off-line calibrating in-line positing method, the system influence is used with the lowest error. The parameters of the adaptive optical system are optimized with the conditional number further. Efficiency method of dealing with the invalid sub-aperture is proposed to improve the far field beam quality very well. With all the new methods, the far field beam quality of the output beams of many solid state slab MOPA lasers are controlled less than 3 and meet the phase distribution demand of the beam combination, in some cases, the β factor can reach to 1.67.