High sensitive detection of near-infrared absorption by surface plasmon resonance

In this letter we report on an operative method for high sensitive measurement of near-infrared absorption based on a surface plasmon resonance (SPR) technique. By coupling with the SPR of a gold film, an absorption band of water near 5173 cm(-1) assigned to a combination of the stretching and bending modes of OH groups is enhanced over 100 times compared with a case without the gold film. In addition, positive and negative enhancements of an absorption depending on the thickness of a gold film were observed as predicted by H. Kano [Appl. Opt. 33, 5166 (1994)]. These experimental results are mathematically well reproduced by use of Fresnel multiple-reflection theory. (C) 2003 American Institute of Physics.