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C. Gasser, J. Ofner, B. Lendl:
"Stand-off hyperspectral imaging - towards mobile, high throughput remote chemical identification and quantification using chemometrics";
Vortrag: ICAVS 9 - International Conference on Advanced Vibrational Spectroscopy, Victoria, Canada; 11.06.2017 - 16.06.2017.

Stand-off Raman spectroscopy is a versatile tool for a variety of applications, such as safety investigations, forensics or geosciences. During the project "OPTIX" (FP7) we showed that the detection of small amounts of explosives and hazardous chemicals at distance of 100 m is possible even through opaque containers. Here, we present a different approach to remote Raman sensing employing hyperspectral Raman spectroscopy. The classical grating as a dispersion element is exchanged in favor of a liquid crystal tunable filter (LCTF), which allows for direct imaging of a selected Raman shift onto the intensified CCD (iCCD). This maintains a high degree of local information and allows for higher throughput, as whole areas can be imaged at once. Measurements with our first prototype, still equipped with a water-cooled, flashlamp-pumped excitation laser, as well as first measurements with a diode pumped, air cooled, small laser are shown. The capability of remote chemical analysis incorporating chemometrics on a reference sample consisting of different polymers will be presented.
Stand-off Raman spectroscopy, where the instrumentation is physically separated from the sample under investigation, can be extremely advantageous for analysis of dangerous, fragile or inaccessible samples. It is mostly used in safety applications, i.e. detection of explosives [1] or geosciences, where the remote detection of minerals on planetary surfaces is desirable [2].
Usually, a pulsed laser point is targeted on the surface of interest, the backscattered
photons are collected using different forms of telescopes and directed towards a
spectrometer. However, when large surface areas must be scanned, it is advantageous
widening the laser spot and using a square detection array to directly image the area
under surveillance. Different kinds of filter can be used to discriminate different Raman
shifts, i.e. acousto-optical filters [3] or, as in this study, LCTFs [4].
The presented prototype can collect Raman spectra from a sample at several meters´
distance (15 m for this study), which are directly loaded into Epina ImageLab [5], a
chemometric analysis program for imaging purposes. A test sample consisting of four
different polymers was measured and different chemometric methods were applied to
increase signal-to-noise ratios and to classify the results.
Furthermore, a compact, air-cooled, diode-pumped laser with high repetition rates
(~10 kHz) was tested to facilitate a mobile prototype with minimal electrical as well as
physical requirements. The results are compared to a stationary, water-cooled and
flashlamp-pumped laser.
[1] A.J. Hobro; B. Lendl; TrAC Trends Anal. Chem. 2009, 28, 1235-1242.
[2] S. Sharma; Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2003, 59, 2391-2407.
[3] J.C. Carter; J. Scaffidi; S. Burnett; B. Vasser; S.K. Sharma; S.M. Angel; Spectrochim.
Acta. A. Mol. Biomol. Spectrosc. 2005, 61, 2288-98.
[4] H. Östmark; M. Nordberg; T.E. Carlsson; Appl. Opt. 2011, 50, 5592-9.
[5] Epina GmbH, www.imagelab.at

stand-off Raman spectroscopy, explosives, chemometrics

http://publik.tuwien.ac.at/files/publik_266595.pdf