In Raman spectroscopy tests,some substances have a fluorescence emission background.Since the fluorescence intensity is generally orders of magnitude higher than the Raman scattering intensity,it is almost impossible to obtain an effective Raman spectroscopy signal during fluorescence interference.In order to suppress the fluorescence background,a near-infrared band laser can be used as the excitation light source,but the quantum efficiency of silicon-based detectors in the band above 1 000 nm is seriously reduced,resulting in the difficulty of near-infrared Raman spectroscopy instruments to detect the band above 3 000 cm-1,that is,there is a problem that the fluorescence suppression effect and detection range cannot be balanced.Since the Raman characteristic peaksat high wavenumber are important for identifying material types and analyzing material structures,such as the N—H telescopic vibration peak of the amino group around 3 300 cm-1 and OH-telescopic vibration peak at 3 650 cm-1.These groups are important for analyzing material corrosion products,hydrates,organic matter,etc.Therefore,a method is urgently needed to solve the problem that the fluorescence suppression effect and detection range cannot be balanced for Raman spectroscopy instruments.In this work,this project proposes a scheme using a spectrometer with fixed detection wavelength,730 and 830 nm dual wavelength laser"relay"excitation(i.e.830 nm excitation of the Raman peaks with low wavenumber,730 nm excitation the Raman peaks with high wavenumber),which can extend the detection range to 200～3 700 cm-1 without reducing the spectral resolution(up to 6 cm-1).At the same time,the whole machine optical path has no mechanical moving parts,and the high reliability is convenient to realize the portable design.The prototype test proved that the technical scheme has the advantages of high sensitivity,good fluorescence suppression effect,wide detection range and high spectral resolution.Through the dual-wavelength near-infrared Raman spectrometer,the clear Raman signal of uranium corrosion products and LiH deliquescence products under organic coating was obtained,which solved the technical problems of non-destructive testing of special materials.This technique is also suitable for other research and testing areas,especially substances with small Raman scattering cross-sections and high fluorescence backgrounds.Since the dual-wavelength NIR Raman spectrometer can cover the detection range of 200～3 700 cm-1,it provides a feasible technical approach for the Raman detection of most hydrate,hydroxyl and amino functional substances.
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