摘要
在光纤阵列光谱合成(SBC)系统中,光纤阵列光源、核心光学元件、内光路等关键单元的非完善因素,如光源发散角、指向偏差及光栅和内光路的热像差等,对合成光束质量的影响同时存在且相互耦合,但尚缺乏其综合退化效应的深入分析。开展了SBC系统的光束质量退化及校正特性研究,建立了非完善因素下的谱合成系统物理模型,进而开展了基于自适应光学(AO)技术的光束质量提升研究,并重点对非共路相位扰动和共路热像差进行了分析讨论。结果表明,AO可以有效地补偿共路热像差,在一定程度上校正非共路相位扰动,进而提升谱合成系统的合成光束质量,从而为实际应用中光纤阵列谱合成系统的光束质量管控提供了参考。
Objective In a fiber array spectral beam combining(SBC)system,imperfections such as installation deviation of the fiber array,linewidth broadening,and thermal effects of the optical elements and internal optical channel coexist and interact with each other,leading to degradation of the combined beam quality.Specifically,the displacement deviation,rotation angle,linewidth broadening,and divergence angle of the fiber laser emitters independently affect the combined beam,leading to noncommonpath phase perturbations in each subbeam.In addition,thermal effects of the diffraction grating and internal optical path introduce aberrations,collectively referred to as commonpath thermal aberrations.As the noncommonpath phase perturbations and commonpath thermal aberrations increase,the degradation of the combined beam quality inevitably becomes more severe.To date,an indepth analysis of the comprehensive degradation effects and correction characteristics of the combined beam quality has been insufficient.Therefore,studying the integrated degradation and correction characteristics of the combined beam quality under these imperfections,particularly with adaptive optics(AO),is crucial for the effective management and control of beam quality in SBC systems.Methods This study presents a theoretical and numerical analysis aimed at improving the beam quality of spectrally combined fiber lasers using adaptive optics.First,a physical model is established for the fiber SBC system for the imperfect factors.It consists of four components:an AObased SBC system,an optical transmission model,a physical model for the thermal deformation of the multilayer dielectric grating(MDG),and a multifield coupling interaction model that describes the lightfluidsolid interactions(LFSMFCI)within the internal optical path.The AObased SBC system is primarily composed of three elements:the SBC,expanding laser beam,and AO systems.Ray tracing and diffraction integral methods are employed to develop and solve the optical transmission model for the SBC system.Additionally,finite element models are constructed for the MDG and LFSMFCI.This enables us to simulate and analyze the temperature distribution and thermal deformation in the MDG and the internal optical path after 60 s of irradiation at an initial temperature of 20℃and a power density of 1000 kW/cm².Subsequently,the degradation mechanisms and characteristics of the combined beam quality are investigated by categorizing the aberrations within the SBC system into two types:noncommonpath phase perturbations and commonpath thermal aberrations.Finally,we discuss strategies for enhancing the spectrally combined beam quality using adaptive optics and simulations.Results and Discussions In the presence of imperfections such as displacement deviation,rotation angle,linewidth broadening,and divergence angle,the intensity distribution of the combined beam irradiating the multilayer dielectric grating displays a Gaussianlike profile that varies with the effect degree of these imperfections.Assuming an initial temperature of 20℃and a power density of 1000 kW/cm²for the incident laser,both the temperature and thermal deformation gradually decrease from the center toward the edge of the MDG after 60 s irradiation,approximating a Gaussianlike distribution.Moreover,the maximum temperature and thermal deformation of the MDG demonstrate a nearly linear increase with increasing incident laser power density(Fig.5).In the axial cross section of the optical transmission,the temperature distribution and heat source distribution of the flow field within the internal optical path align with the Gaussianlike distribution of the laser irradiation.The peak values of the temperature and heat source are situated at the center of the optical path and reflector,respectively(Fig.7).The accumulated optical path difference induced by thermal effects in the gas is the primary contributor to the optical path differences,which significantly exceeds the thermal deformation on the surface of the reflector(Fig.8).Under the influence of noncommon path phase perturbations and common path thermal aberrations,the farfieldβfactor of the combined beam increases,indicating deteriorating beam quality.After correction with the AO system,the farfieldβfactor decreases and approaches 1,demonstrating a significant improvement in the quality of the combined beam(Fig.10).Under the specific boundary conditions considered,the rotation angle of the fiber array is identified as the primary factor affecting output beam quality.When the variance of the rotation angle exceeds 1.5 mrad,the corrected farfieldβfactor remains higher than 1.5,indicating that the beam quality is still inadequate.Additionally,the degradation of the beam quality caused by the commonpath thermal effects and optical path is comparatively less severe than that caused by noncommonpath phase perturbations.The thermal effects are nearly uniform across each subbeam in the SBC system,making the correction through AO more manageable.The AO system exhibits superior correction capabilities for loworder common path aberrations resulting from thermal effects as opposed to highorder aberrations,thereby significantly enhancing the combined beam quality of the SBC system(Fig.12).Conclusions This study investigates the degradation and correction characteristics of the fiber array SBC system based on the established physical model of the fiber array with imperfect factors.The results indicate that both noncommonpath phase perturbations and commonpath thermal aberrations degrade the combined beam quality,which can be corrected by the AO system.Notably,AO demonstrates better correction capabilities for commonpath thermal aberrations than for noncommonpath phase perturbations.However,the combined beam quality after correction with the AO is still not sufficient for practical applications,particularly when the degradation of the combined beam quality is severe because of aberrations in the SBC system.Therefore,the control and management of the fiber array and other optical elements are crucial for reducing noncommonpath phase perturbations and alleviating the effects of commonpath thermal aberrations within the SBC system.
作者
李志慧
张凯
胡武利
冯明霞
贾凯
钟哲强
张彬
Li Zhihui;Zhang Kai;Hu Wuli;Feng Mingxia;Jia Kai;Zhong Zheqiang;Zhang Bin(College of Electronics and Information Engineering,Sichuan University,Chengdu 610064,Sichuan,China;Southwest Institute of Technical Physics,Chengdu 610041,Sichuan,China)
出处
《中国激光》
北大核心
2025年第11期195-205,共11页
Chinese Journal of Lasers
基金
中国兵器工业集团有限公司激光器件技术重点实验室开放基金(KLLDT202307)。
关键词
光纤阵列
光谱合成
热效应
光束质量
自适应光学校正
fiber array
spectral beam combining
thermal effects
beam quality
correction with adaptive optics
