Study Of Fluorescence Rejection Method In Portable Raman Spectroscopy

Raman spectroscopy is widely used in the field of food safety, drug safety andenvironmental pollution detection. The emergence of portable Raman spectrometer furtherpromote the application of Raman spectroscopy. However, Raman detection and analysisare often disturbed by fluorescence background. Fluorescence disturbance significantlyaffect Raman peak’s recognition and quantitative sample analysis. Many fluorescencerejection methods commonly used in the laboratory Raman system cannot be applied to theportable Raman spectrometers for the limitations in size, cost, power consumption andoperation environment. Therefore it’s important to study the fluorescence suppressionmethod in portable Raman spectrometer. The shifted-excitation Raman differencespectroscopy (SERDS) has the characteristics of good fluorescence rejection performance,wide application scope, and the potential of miniaturization. In order to apply the SERDSmethod in portable Raman spectrometer, two problems must be solved: one is the portablemulti-wavelength excitation source and the other is the robust algorithm for restoring thenormal Raman signal from the difference spectrum.In this paper, a low-cost, portable external cavity diode laser(ECDL) based on Littrowstructure has been proposed and implemented. A wavelength tuning range of15nm can beachieved, with spectral line-width less than0.3nm, and the output laser power up to80mW.Such features make it suitable for SERDS light source. And it has the potential to beembedded in portable instruments. In this paper, a robust recovery alogrithm for differencespectrum, i.e. the multiple-constraint iterative deconvolution alogrithm, was alsointroduced. We extended this algorithm to make it suitable for the situation of multiple-wavelength excitation. Through simulation and anlysis, it’s concluded that more excitation wavelengths result in less distortion of the restored Raman signal.Using the home-made ECDL, a SERDS Raman spectroscopy measurement systemwas built. And several illegal food additives (Sudan I, Rhodamine B, melamine, Hexamine)were tested. The results prove that SERDS method can effectively remove fluorescencebackground, and the multi-constraint iterative deconvolution algorithm can reliably restorethe normal Raman signal from the difference spectrum. Then we excited the sample ofSudan I with three wavelengths and verified the performance of the multiple-constraintalgorithm for the situation of multi-wavelength excitation.