Paper No. 10
Presentation Time: 3:45 PM


STOLOW, Albert, Molecular Photonics, National Research Council Canada, 100 Sussex Drive, Ottawa, ON K1A 0R6, Canada, SLEPKOV, A.D., Department of Physics and Astronomy, Trent University, Peterborough, ON K9J 7B8, Canada, PEGORARO, Adrian, Molecular Photonics, National Research Council Canada, Ottawa, ON K1A 0R6, Canada and BURRUSS, Robert C., Eastern Energy Resources Science Center, U. S. Geological Survey, MS 956, National Center, 12201 Sunrise Valley Drive, Reston, VA 20192,

Nonlinear optical responses of materials have been developed into important methods for spectroscopy and label-free real-time microscopy in biomedical research. During experiments characterizing the C:H content of organic matter in shale gas source rocks, we demonstrated that the third-order nonlinear process coherent anti-Stokes Raman scattering (CARS) permits non-destructive imaging of 3D distributions of hydrocarbon-rich fluid inclusions in minerals, with submicrometer resolution (Burruss et al., in press, Geology). Furthermore, two additional nonlinear responses, two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) are generated simultaneously with CARS, providing three co-localized images with contrast due to molecular vibrations (CARS), fluorescence (TPEF), and structural discontinuities (SHG). These methods have a number of advantages for the imaging and analysis of geologic materials. The localization of the nonlinear signal within the center of the focus of a high numerical aperture objective results in high contrast and excellent Z-sectioning for 3D imaging. Because CARS is a coherent, stimulated process, the signal is 4 to 5 orders of magnitude more intense than conventional, spontaneous Raman scattering. This has allowed us, for the first time, to separate the Raman C-H stretching mode of aliphatic hydrocarbons from intense fluorescence of aromatic hydrocarbons within petroleum fluid inclusions. Our multimodal CARS microscope (Pegoraro et al. Optics Express 2009; 17: 2984) is based on a modified laser scanning confocal microscope with a single tunable femtosecond Ti:Sapphire laser as the source, and has Raman tunablity from ~900 to 4500 cm-1. The high signal levels allows short (2 to 8 μs) pixel dwell times, providing rapid imaging of large (350 x 350 x 100 μm) 3D fields of view within minutes. We can routinely generate images or spectra based on the distribution of C-H, N=N, P=O, C=C, C=O or O-H stretching vibrations. We have recently generated CARS images of diamond and carbonate and phosphate minerals at 1333, 1088, and 980 cm-1, respectively. We believe that CARS microscopy and spectroscopy and related nonlinear imaging modalities will have broad applications across the geosciences.
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