M. Maiwald, A. Müller, B. Sumpf and G. Tränkle

Published in:

J. Raman Spectrosc., vol 47, no. 10, pp. 1180-1184 (2016).

Abstract:

In this paper, we present a portable shifted excitation Raman difference spectroscopy (SERDS) system applied in outdoor experiments. A dual-wavelength diode laser emitting at 785 nm is used as excitation light source. The diode laser provides two individually controllable excitation lines at 785 nm with a spectral distance of about 10 cm^-1 for SERDS. This monolithic light source is implemented into a compact handheld Raman probe. Both componentswere developed and fabricated in-house. SERDS measurements are performed in an apple orchard, and apples and green apple leafs are used as test samples. For each excitation wavelength, a single Raman spectrum is measured with 50 mW at the sample. Strong background interference from ambient daylight and laser-induced fluorescence obscure the Raman signals. SERDS efficiently separates the wanted Raman signals from the disturbing background signals. For the Raman spectroscopic investigations of green leafs, one accumulationwith an exposure time of 0.2 s was used for each excitation wavelength to avoid detector saturation. An 11-fold improvement of the signal-tobackground noise is achieved using SERDS. The results demonstrate the suitability of the portable SERDS systemfor rapid outdoor Raman investigations.

Keywords:

shifted excitation Raman difference spectroscopy; SERDS; 785nm; diode laser; handheld probe.

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