太赫兹波段豆油光谱的优化测量  

Study on the Measurement and Optimization of Soybean Oil Optical Spectrum in THz Range

作　　者：周胜灵[1] 祝诗平[1] 李光林[1] 黄杰[1] 杨亚玲[2] 

机构地区：[1]西南大学工程技术学院,重庆400715 [2]西南大学物理科学与技术学院,重庆400715

出　　处：《光谱学与光谱分析》2016年第4期924-928,共5页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金青年基金项目(61401373);中央高校基本科研业务费专项资金项目(XDJK2014C132);重庆市应用开发计划项目(cstc2014yykfA80006)资助

摘　　要：太赫兹时域光谱技术是基于飞秒超快激光技术的有效的光谱检测技术,太赫兹波独特的优势使其成为一种有效的无损检测手段,并被广泛地应用到各个领域。然而在样品检测尤其是液体样品检测过程中,由于Fabry-Perot效应的存在,太赫兹波在样品、样品容器、以及光学元件之间的多次反射,使时域信号产生回波,样品的吸收光谱在频域内产生振荡,有可能会隐藏一些重要的吸收特征。为了解决这一问题,对解卷积算法进行改进,在传统计算模型的基础上,考虑系统中液体池窗片和光学元件对太赫兹波的非线性吸收,将包含回波的太赫兹时域信号描述为太赫兹主脉冲与一系列冲击信号和非线性传递函数的卷积。通过分析,有效去除回波引起的频谱振荡,进一步提高太赫兹波段豆油光学参数的测定精度。实验对比了改进前后0.2～2THz波段豆油的频谱及吸收谱,实验结果证明,与传统的主脉冲截取法相比,本算法不仅能有效去除回波引起的频谱振荡,且在相同检测条件下,可将太赫兹波段豆油样品的频率分辨率由50GHz有效提高至10GHz。该算法不受被测对象参数的影响,同样适用于其他液体的太赫兹时域光谱测量。最后对吸收谱中残余的频谱振荡进行了深入分析。Terahertz time-domain spectroscopy is an effective technique that applies spectral measurements by using an ultra fast femtosecond laser.These unique properties of terahertz waves make it an effective nondestructive testing technology.Currently,it has been applied in many fields.However,when we calculate the optical parameters of the sample especially for liquids,from data obtained with time-domain spectroscopy,a common problem occurred is spurious oscillation,which is caused by the FabryPerot effect in sample,containers and optical elements.In order to obtain high frequency resolution and accurate sample optical parameters,it is necessary to use some signal processing techniques properly.In this paper,we improved de-convolution algorithm and presented a simple algorithm based on the traditional optical parameter calculation model.Considering the nonlinear absorption of THz wave by samples,containers,emitters or detectors,a THz time-domain trace containing echo signals can be represented as a convolution of the primary peak,some delta functions and nonlinear transfer functions.By analyzing equations,spurious oscillations in the THz spectra result from echo signals can be removed or reduced effectively.The use of the method is discussed and the transmission spectrum of soybean oil in 0.2～2.0THz range is measured accurately by terahertz time-domain spectroscopy.Experiments show that,this method can effectively remove the frequency oscillation caused by echoes.This algorithm is not affected by the tested object,and is equally applicable to other liquid measurements in THz range.What＇s more,compared with the traditional method of main pulse interception,this algorithm under the same experimental conditions can effectively improve frequency resolution of soybean oil in 0.2～2.0THz region,from 50 GHz to less than 10 GHz.At the end of this paper,the causation of remaining oscillation in sample spectrum and absorption spectrum were deeply analyzed.

关 键 词：太赫兹时域光谱 频谱振荡 吸收系数 豆油 

分 类 号：O439[机械工程—光学工程]