25 February 2010 Ultrasensitive Raman sensor based on a highly scattering porous structure
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Analytical methods capable of in situ monitoring of water quality have been in high demand for environmental safety, the identification of minute impurities and fundamental understanding of potential risks of these molecular species. Raman spectroscopy, which provides 'fingerprint' information about molecular species in the excitation volume, is a powerful tool for in vivo diagnostics. However, due to a relatively weak Raman signal (~ 1 out of 1014 incident photons produces the useful signal) there is a need to significantly (by many orders of magnitude) enhance this signal, to raise the detection sensitivity of this technique. Traditionally, surface enhanced Raman spectroscopy is employed to dramatically increase the local field intensity and substantially improve the efficiency of Raman scattering. However, the above enhancement occurs only in "hot spots", which represent only a small percent of the total surface are of the substrate. Plasmonic nanostructures are also found to be hard to manufacture in large quantities with the desired degree of reproducibility and to be unable to handle high laser power. We propose and experimentally demonstrate a new type of approach for ultrasensitive Raman sensing. It is based on manufacturing a random porous structure of high-index material, such as GaP, and use the effect of light localization to help improving the detection sensitivity of such sensor. The desired structure was manufactured using electrochemical etching of GaP wafers. The observed Raman signal amplitudes are favorably compared to the best known plasmonic substrates.
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V. V. Yakovlev, V. V. Yakovlev, } "Ultrasensitive Raman sensor based on a highly scattering porous structure", Proc. SPIE 7553, Frontiers in Pathogen Detection: From Nanosensors to Systems, 75530H (25 February 2010); doi: 10.1117/12.842285; https://doi.org/10.1117/12.842285

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