Xu Lijun, Liu Chang, Zheng Deyan, Cao Zhang, Cai Weiwei
Ministry of Education's Key Laboratory of Precision Opto-mechatronics Technology, School of Instrumentation and Opto-Electronic Engineering, Beihang University, Beijing 100191, China.
Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, United Kingdom.
Rev Sci Instrum. 2014 Dec;85(12):123108. doi: 10.1063/1.4903356.
To realize on-line high-accuracy measurement in direct absorption spectroscopy (DAS), a system-on-chip, high-precision digital signal processor-based on-line Voigt lineshape fitting implementation is introduced in this paper. Given that the Voigt lineshape is determined by the Gauss full width at half maximum (FWHM) and Lorentz FWHM, a look-up table, which covers a range of combinations of both, is first built to achieve rapid and accurate calculation of Voigt lineshape. With the look-up table and raw absorbance data in hand, Gauss-Newton nonlinear fitting module is implemented to obtain the parameters including both the Gauss and Lorentz FWHMs, which can be used to calculate the integrated absorbance. To realize the proposed method in hardware, a digital signal processor (DSP) is adopted to fit the Voigt lineshape in a real-time DAS measurement system. In experiment, temperature and H2O concentration of a flat flame are recovered from the transitions of 7444.36 cm(-1) and 7185.6 cm(-1) by the DSP-based on-line Voigt lineshape fitting and on-line integral of the raw absorbance, respectively. The results show that the proposed method can not only fit the Voigt lineshape on-line but also improve the measurement accuracy compared with those obtained from the direct integral of the raw absorbance.
为了在直接吸收光谱法（DAS）中实现在线高精度测量，本文介绍了一种基于片上系统、高精度数字信号处理器的在线沃伊特线型拟合实现方法。鉴于沃伊特线型由高斯半高宽（FWHM）和洛伦兹FWHM决定，首先构建一个查找表，该表涵盖两者的一系列组合，以实现沃伊特线型的快速准确计算。有了查找表和原始吸光度数据，实现高斯 - 牛顿非线性拟合模块以获得包括高斯和洛伦兹FWHM在内的参数，这些参数可用于计算积分吸光度。为了在硬件中实现所提出的方法，采用数字信号处理器（DSP）在实时DAS测量系统中拟合沃伊特线型。在实验中，通过基于DSP的在线沃伊特线型拟合和原始吸光度的在线积分，分别从7444.36 cm(-1)和7185.6 cm(-1)的跃迁中恢复了扁平火焰的温度和H2O浓度。结果表明，与从原始吸光度的直接积分获得的结果相比，所提出的方法不仅可以在线拟合沃伊特线型，还可以提高测量精度。
