| At present,the adaptive optical system based on the wavefront sensor can efficiently and stably purify the beam,which is the main method for improving the beam quality of high-energy laser systems.However,this method requires wavefront measurement and the system is bulky,making it difficult to meet the needs of miniaturization.there are higher requirements for beacon sources and it is difficult to improve the closed-loop bandwidth.In order to solve the above problems,this paper proposes a wavefront-free adaptive optical system that uses the eigen mode of the deformable mirror and the characteristics of the far-field spot for processing and analysis to correct the square laser beam outputting by the laser.This method abandons the wavefront sensor,the cost is lower,the volume is smaller,and it has broad application prospects.In this paper,the square beam with a wavelength of 1064nm outputting by the laser is used as the object of beam purification.Based on the mathematical expression of the influence function of the deformable mirror and the characteristics of the measured light intensity information of the far field,the theoretical research and simulation verification of beam purification are completed.The correction effect of this method was experimentally verified.Some influencing factors are analyzed.The components of adaptive optics system,the correction methods commonly used in adaptive optics correction system based on wavefront sensor and adaptive optics system without wavefront sensor are introduced.The advantages of wavefront sensorless correction system are explained and the research purpose and significance of this subject are clarified.The basic principles of the correction method of the wavefront sensorless adaptive optical system based on the eigen mode of the deformable mirror and the far-field measurement are elaborated in detail,and the calculation process of the eigenmode of the deformable mirror and the system evaluation function,mode coefficients and correction voltage are derived.Aiming at the 67-unit deformable mirror used in the experiment,the influence function model and the eigenmode model were established,and the correction effects of Zernike polynomial aberration,two-dimensional Legendre polynomial aberration and aberration generated by applying random voltage were simulated and verified.For Zernike polynomial aberrations with a PV value of 4.704 ?m and an RMS value of 0.521 ?m,the PV value is 1.156?m and the RMS value is 0.082 ?m after closed-loop correction;Legendre polynomial aberration,after closed-loop correction,the PV value is 0.915 ?m,and the RMS value is 0.054?m;for the PV value is 2.732 ?m,the RMS value is 0.528 ?m,and the aberration generated by applying a random voltage,the PV value after two corrections 0.028 ?m,RMS value is 0.005?m.The effect of response rate coefficient on the decomposition of eigenmode is analyzed.Compared with the correction effect and the number of corrections of the SPGD algorithm,when the same correction effect is achieved,the deformed mirror of this method needs to produce 135 face shape changes,and the SPGD algorithm requires the deformed mirror to produce about 2700 deformations.An experimental system calibration platform was built,and the automatic control of the platform was programmed.The influence function of the deformable mirror was collected,and the eigenmode was obtained.The eigenmode was used in the correction system to verify the feasibility of the correction method proposed in this paper for correcting the static small aberration system.For the original wavefront with a PV value of 2.057 ?m and an RMS value of 0.3753 ?m,the corrected PV and RMS values are 0.507 ?m and 0.0959 ?m,respectively.When the eigenmode with a larger proportion is selected for priority correction,for the original wavefront with a PV value of 1.36 ?m and an RMS value of 0.1995 ?m,the corrected PV value and RMS value are 0.514 ?m and 0.088 ?m,respectively.The correction of the mode coefficient does not affect the correction effect,and the correction speed is improved.The corrected wavefront is decomposed by Zernike polynomial,and the correction ability of the correction method for various aberrations is analyzed. |
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