Optical-mechanical System Design For Beam Quality Evaluation Of Rectangular Large-aperture Near-infrared Laser

Since the birth of lasers,they have become increasingly used in the military,aerospace,social,and other industries.Laser beam quality is one of the primary indicators for assessing laser performance.Adaptive optics technology plays a significant role in enhancing laser beam quality.The ability to accurately measure the degree of beam quality improvement is crucial for the advancement of laser technology.Because the laser output beam is rectangular due to the structural properties of the slab-shaped gain medium,it is important to implement multi-parameter measurement and assessment of the rectangular aperture laser beam,including wavefront,beam quality,and uniformity.In addition,as the output aperture of solid-state slab lasers grows,the design challenge of laser beam quality evaluation systems grows.This challenge is in achieving large-aperture and multi-parameter measurement and evaluation while meeting the demands of conjugate imaging,athermalization,and small volume.The rectangular large-aperture near-infrared laser beam quality evaluation system is the subject of research in this paper based on the aforementioned issues.The primary work is as follows:（1）The existing beam quality evaluation system and methods are summarized and analyzed,and the characteristics of the output beam of solid-state slatted laser are studied and analyzed,which provides support for the formulation of schemes.By analyzing the typical telescope optical system and combining the conjugate imaging principle of the Keplerian system,the technical method of using large-magnification beam compression was determined,and combining aspheric technology to meet the design requirements of large aperture and small volume.The detection scheme of common aperture and the multi-channel splitting beam is further adopted to solve the multi-parameter measurement.（2）The technical indicators of the optical system are designed and analyzed,and the initial structural parameters of each detection unit are analyzed,calculated,and determined by combining aberration theory and telephoto imaging theory.The optical design software is used to optimize the initial structural parameters and carry out the heatless design,and the rectangular large-aperture near-infrared laser beam quality evaluation optical system model is obtained,and the imaging quality is optimized and analyzed.Finally,the Monte Carlo method is used to analyze the tolerance and analyze the influence of processing and assembly errors on the image quality of the system.（3）The mechanical structure of the main frame and sub-units of the evaluation system is designed.The finite element analysis method is employed to analyze and estimate how the deformation of the optical system and mechanical structure caused by gravity and temperature affects the optical system’s images.The simulation structure shows that under gravity load,the system deformation is small,and the imaging quality is almost not affected.The system’s wave aberration PV value is less than 0.23λunder the combined stress of gravity and temperature,which satisfies the criteria of engineering applications.（4）To test the viability and stability of the evaluation system design scheme,a rectangular large-diameter near-infrared laser beam quality assessment system test platform was constructed.The experimental findings demonstrate that the system is stable in the20±10°C temperature range.The maximum variation of system wavefront aberration PV,wavefront aberration RMS,beam qualityβfactor,and uniformity are each equal to PV=0.022μm,RMS=0.012μm,Δβ=0.058 times diffraction limit,and₉)=0.098,respectively.It is consistent with the trend toward compact and lightweight photoelectric instrument and has some reference value for multi-parameter detection and lightweight miniaturized design of beam quality evaluation system.