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R. J. Saykally (University of California, Berkeley)
In order to characterize the chemical composition of extraterrestrial materials (e.g. the organic content of the cometary and interstellar particles returned from the STARDUST mission), progress has been made in developing high spatial resolution vibrationally-selective microscopy techniques. To more readily quantify the relative contribution from aliphatic vs. aromatic hydrocarbons, multiple vibrations must be simultaneously excited to allow for direct comparison between peaks in the spectrum. To this end, we developed a multiplex coherent anti-Stokes Raman scattering (CARS) microscope, using chirped femtosecond laser pulses to achieve high spectral resolution images of model samples. As shown both experimentally and theoretically, the spectral resolution depend not only on the extent of the chirp, but on which pulses were chirped as well. When applied to microscopy, images of polystyrene beads show vibrational contrast arising from the C-H stretches, as seen in the point-specific spectra collected on and off the beads. By imaging selected spectral regions of the spectrum, chirped CARS microscopy shows promise for obtaining high spatial resolution, chemically specific images of the STARDUST samples.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.