摘要
准确获取飞秒激光成丝横截面图像及其沉积能量空间分布信息,对于成丝动力机制研究和促进诸多基于光丝的实际大气应用发展具有重要意义。本文基于热传导方程和波动方程构成的光声信号前向仿真模型,理论模拟了利用环阵式光声层析系统接收飞秒激光在空气介质中成丝诱导产生超声脉冲信号的过程;然后,利用延迟叠加算法对飞秒激光大气传输成丝沉积能量横向分布图像进行了反向重建,并分析了测量系统中关键器件超声换能器的中心频率、带宽、表面尺寸和探测表面灵敏度等性能参数对光丝沉积能量分布图像重建结果的影响。结果表明,单丝诱导产生的声压脉冲信号频谱为单峰结构,而多丝声压脉冲信号频谱为多峰结构;相比于单丝图像重建,多丝图像重建受“孔径效应”影响更显著;换能器的性能参数对光丝图像的重建效果有显著的影响,换能器的带宽越大、表面直径越小,以及表面灵敏度系数越大,越有利于光丝沉积能量分布图像重建效果的提升。该研究结果可为真实大气条件下飞秒激光传输成丝沉积能量空间分布的实验测量提供一定的理论支撑。
Objective Filament refers to a plasma channel with high laser intensity and high plasma density formed by the propagation of intense femtosecond laser pulses in a transparent medium.Several literatures have shown that the crosssection image of an optical filament at a specific z usually contains abundant structural information such as filament diameter,length,and energy distribution,which is of great significance for the visualization study of the dynamic process of filament formation.Moreover,accurate acquisition of the spatial structure and energy deposition distribution of femtosecond optical filaments are also of great significance for the development of filamentation-based atmospheric applications.Nevertheless,it is also the inherent parameter most difficult to measure directly.To solve the problem,we introduce a new medical imaging method named photoacoustic tomography(PAT)for optical filament cross-section imaging.The feasibility of reconstructing monofilament and multifilament images by photoacoustic tomography is verified theoretically.Moreover,we also study the influence of the performance parameters of the ultrasonic transducers on the optical filament image reconstruction.Methods We adopt a forward simulation model based on the photoacoustic wave equation to simulate the acquisition process of ultrasonic signals induced by optical filaments in air.A circular-scanning-based PAT system is considered to obtain the cross-section image of the laser filament.To simplify the problem,we assume that the initial heat source distribution of the optical filament satisfies the Gaussian distribution form,which can represent both the small high-energy core of the optical filament and its weak background energy region with a larger range.Based on experimental measurements,the initial maximum energy deposition density is assumed to be in the order of 10 mJ/cm^(3),and the diameter of the heat source is assumed to be in the order of 100μm.The simulated time series of the acoustic signal is then applied to reconstruct t
作者
曾庆伟
刘磊
胡帅
李书磊
赵世军
Zeng Qingwei;Liu Lei;Hu Shuai;Li Shulei;Zhao Shijun(College of Meteorology and Oceanography,National University of Defense Technology,Changsha 410073,Hunan,China;High Impact Weather Key Laboratory of China Meteorological Administration,Changsha 410073,Hunan,China)
出处
《光学学报》
EI
CAS
CSCD
北大核心
2024年第12期101-111,共11页
Acta Optica Sinica
基金
湖南省自然科学杰出青年基金(2021JJ10047)
湖南省自然科学青年基金(2021JJ40664)
国家自然科学基金(42105176,42105137)
国防科技大学科研计划(ZK21-40,ZK21-27)。
关键词
飞秒激光
激光成丝
能量沉积
光声信号
超声换能器
反投影
femtosecond laser
laser filamentation
energy deposition
photoacoustic signal
ultrasound transducer
back projection
