摘要
在太赫兹光谱实验测试中,为了提高系统信噪比,被测试的固态样品表面通常为平行且光滑的形态,然而在安检等实际应用场合中,自然状态下的物体表面可能会呈现出凹陷、凸起等特殊形态,这会对太赫兹光谱产生影响,这些影响与特殊形态的尺寸有关,但最容易忽视的是这些影响也与太赫兹波的空间分布有关。首先,对凹陷表面样品进行了基于高斯光学的太赫兹波透射过程建模,研究了表面具有规则圆柱形的凹陷表面形态对太赫兹透射光谱的影响。通过小孔拟合法对太赫兹光谱系统的高斯光学参数进行了测量,获得了太赫兹波的束腰半径等参数。然后,选用表面被加工成凹陷形态的聚四氟乙烯为实验材料进行太赫兹透射光谱实验,将太赫兹光谱传递函数幅值的理论模型值和实验值进行对比来验证模型的适用情况,通过实验证实了在表面有凹陷等缺损情况时将太赫兹波进行高斯光束建模的必要性。最后,由模型推论出在与太赫兹波传播方向平行和垂直两个维度方向上,凹陷深度和凹陷半径对太赫兹透射光谱的定量影响作用:随着凹陷深度的增加,光谱传递函数幅值周期越来越小,两者之间存在单调的定量关系,且不会受到凹陷半径的影响。利用凹陷深度对光谱传递函数幅值周期的定量影响关系可以实现对凹陷深度的定量检测,当可用频谱宽度为1.2 THz时,凹陷深度的最低检测值为0.53 mm;随着凹陷半径的增加,光谱传递函数幅值均值有着先降低后增加的变化趋势,两者之间不存在单调函数关系且受到凹陷深度的影响。当凹陷半径大于5 mm时,光谱传递函数幅值均值不再随半径的增加而增大,样品表面凹陷对太赫兹波光谱传递函数幅值幅度的影响与凹陷位置也有关系,这两种现象主要与太赫兹波的高斯分布情况有关。研究结论可用于太赫兹波在非极性材料表面缺陷的无损检测中,还可用于设计样品表面形态,使其具有期望的光谱传递函数。
In the terahertz spectroscopy experiment,the tested solid sample's surface is usually parallel and smooth to improve the system's signal-to-noise ratio.However,the object's surface in its natural state may show particular morphology such as depression and bulge,which will affect the terahertz spectrum in practical applications such as security inspection.These effects are related to the size of the particular morphology,but the most easily overlooked is that these effects are also related to the spatial distribution of terahertz waves.In this paper,firstly,we establish a model according to the terahertz transmission process of concave surface samples based on Gaussian optics.The influence of the regular cylinderconcave surface on the terahertz transmission spectra is studied.The Gaussian optical parameters of the terahertz spectrum system are measured by the small-aperture fitting method,and the parameters such as the beam waist radius of the terahertz wave are obtained.Then,polytetrafluoroethylene with a regular cylinderconcave surface is selected as the experiment material.The theoretical model value of transfer function amplitude is compared with the experiment value to verify the model's applicability.The necessity of taking a terahertz wave as the Gaussian beam when there are defects such as a concave surface is confirmed through the experiment.Finally,it is inferred from the model that the quantitative effects of depression depth and depression radius on terahertz transmission spectra,in the directions parallel and perpendicular to the propagation direction of terahertz wave:with the increase of depression depth,the spectral transfer function amplitude period becomes smaller and smaller.It is a monotonous quantitative relationship that will not be affected by the depression radius.The quantitative detection of depression depth can be realized using this quantitative relationship between depression depth and the spectral transfer function amplitude period.When the available spectra width is 1.2 THz,the minimum detection limit of depression depth is 0.53 mm;With the increase of depression radius,the average spectral transfer function amplitude decreases first and then increases.There is no monotonic function relationship between them,which is affected by depression depth.When the depression radius is greater than 5 mm,the mean value of the spectral transfer function amplitude no longer increases with the increase of the radius.The influence of the depression on the spectral transfer function amplitude is also related to the depression position.These two phenomena are mainly related to the Gaussian distribution of the terahertz waves.The conclusions of this study can be used in the nondestructive testing of surface defects of nonpolar materials by terahertz wave.They can also be used to design the surface morphology of samples to make them have the desired spectral transfer function.
作者
于洋
张朝晖
赵小燕
张天尧
李迎
李星玥
吴先毫
YU Yang;ZHANG Zhao-hui;ZHAO Xiao-yan;ZHANG Tian-yao;LI Ying;LI Xing-yue;WU Xian-hao(School of Automation and Electrical Engineering,University of Science and Technology Beijing,Beijing 100083,China;Beijing Engineering Research Center of Industrial Spectrum Imaging,Beijing 100083,China)
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2023年第9期2843-2848,共6页
Spectroscopy and Spectral Analysis
基金
国家重点研发计划项目(2021YFA0718901),国家自然科学基金项目(62005014),中央高校基本科研业务费专项资金项目(FRF-TP-20-015A1)。
关键词
太赫兹光谱技术
透射模型
表面形态
高斯光学
Terahertz spectroscopy
Transmission model
Surface morphology
Gaussian optics
