Ikehata A, Ohara K, Ozaki Y. Direct determination of the experimentally observed penetration depth of the evanescent field via near-infrared absorptions enhanced by the off-resonance of surface plasmons.
APPLIED SPECTROSCOPY 2008;
62:512-516. [PMID:
18498692 DOI:
10.1366/000370208784344460]
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Abstract
Recently, absorption-sensitive surface plasmon resonance (SPR) techniques have attracted much attention. SPR near-infrared spectroscopy (SPR-NIRS) based on the Kretschmann configuration is one of the techniques for absorption enhancement. The enhanced spectrum obtained by SPR-NIRS basically corresponds to the measurement of an NIR absorption spectrum with a very short path length. However, the path length cannot be applied for Lambert's law due to the enhanced evanescent field. A direct determination of the penetration depth of the evanescent field is carried out via NIR absorptions enhanced by the off-resonance of surface plasmons, which is a principle of SPR-NIRS. The signal intensities of the enhanced NIR spectra of micrometer-thick polymer films having various thicknesses are compared with the classic theory of penetration depth. It is confirmed that the effective depth of the SPR-NIRS measurement can be expressed by the classic theory of penetration depth of the evanescent field proposed by Harrick.
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