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C. Gasser, T. Aichinger, J. Ofner, B. Lendl:
"Stand-off Spatially Offset Raman spectroscopy: towards 3D stand-off imaging";
Poster: 11th Symposium Confocal Raman Imaging, Ulm, Germany; 29.09.2014 - 01.10.2014; in: "11th Symposium Confocal Raman Imaging", (2014), 1 S.

Stand-off Raman spectroscopy is a versatile tool in a range of analytical applications, such as safety (detection of explosives at safe distances) or geosciences (planetary exploration). Recently, also spatially offset Raman spectroscopy (SORS), which allows layer discrimination and thereby 3D depth profiling of unknown samples, was implemented into stand-off techniques. However, the combination of stand-off imaging techniques and SORS still has to be investigated thoroughly.
Hence, we present a setup for stand-off SORS spectroscopy. It consists of a frequency doubled Nd:YAG (operating at 532 nm) laser with a pulse length of 4.4 ns and a repetition frequency of 10 Hz as light source. The backscattered light is collected using a 6 inch Schmidt-Cassegrain telescope, coupled into an Acton (SP-2750) spectrograph using an optical fiber and detected at a PIMAX 1024RB iCCD camera (Figure 1). The camera gate width was set to 5 ns. The laser and camera are synchronized in order to minimize unwanted influence from daylight and fluorescence, so that the actual Raman signal is maximized. The laser pulse energy was adjusted to 20 mJ. In order to set the correct spatial offset between laser spot and telescope, an adjustable mirror, controlled by two motorized actuators (ThorLabs ZST213), was installed.
We report first results on SORS of a series of two-layer systems consisting polymer sheets of various thicknesses containing powdered compounds, which show distinctive bands in the Raman spectrum. The sample arrangement was placed at 12 m from the telescope. Application of statistics based spectral post-processing to the image will be demonstrated.

stand-off Raman, 3D