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Dual-wavelength Raman fusion spectroscopy Johannes Kiefer Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b03909 • Publication Date (Web): 10 Jan 2019 Downloaded from http://pubs.acs.org on January 16, 2019
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Analytical Chemistry
Dual-wavelength Raman fusion spectroscopy Johannes Kiefer1,2,3,*
1Technische
2School 3Erlangen
Thermodynamik and MAPEX Center for Materials and Processes, Universität Bremen, Badgasteiner Strasse 1, 28359 Bremen, Germany
of Engineering, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom Graduate School in Advanced Optical Technologies (SAOT), Friedrich-AlexanderUniversität Erlangen-Nürnberg, 91052 Erlangen, Germany
*Corresponding author. Email:
[email protected] 1 ACS Paragon Plus Environment
Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Abstract Spatially compressed dual-wavelength Raman spectroscopy allows recording the full Raman spectrum using a detection system with limited spectral range. The common approach is to record the spectra with the two excitation lasers consecutively and then concatenate the full spectrum. However, with this approach quantitative analysis for process monitoring is not possible as the investigated object may change between the two acquisitions. In this Note, spectral fusion is proposed as a concept to overcome this problem. The sample is illuminated by the two lasers simultaneously hence leading to an on-chip fusion of the different parts of the Raman spectrum. It is shown that the resulting data are suitable for quantitative evaluation using univariate and multivariate methods. Dual-wavelength Raman fusion spectroscopy offers new opportunities for building highly compact devices for analytical chemistry. Keywords: Raman spectroscopy; data processing; principal component analysis;
2 ACS Paragon Plus Environment
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Analytical Chemistry
Raman spectroscopy utilizing multiple excitation wavelengths has been proposed for a number of analytical applications. The most common technique in this regard is shifted excitation Raman difference spectroscopy (SERDS), in which two Raman spectra are recorded with slightly shifted laser wavelength in order to obtain a fluorescence free difference spectrum 1-5. The wavelength shifts are typically smaller than 1 nm in order to ensure that the Kasha-Vavilov rule holds and high-quality Raman spectra can be reconstructed 6,7. Larger shifts were found to be not suitable as they lead to awkward line shapes and a loss of information 6. Beyond SERDS, however, larger wavelength separation can be useful. For instance, a dual-wavelength Raman method was proposed for fluid phase equilibrium studies 8. For this purpose, the first and second harmonic radiation of a Nd:YAG laser was employed to study the liquid and gas phase, respectively, of a vapor-liquid two-phase system. The near-infrared Raman enabled highresolution spectroscopy with reasonable signal intensity in the liquid, while the green laser allowed recording spectra from the vapor phase. Another dual-wavelength Raman technique was recently introduced by Cooper et al. 9, who designed a spatially compressed dualwavelength excitation Raman spectrometer. In their concept, a spectrometer with a limited detection range of
