Wavelength dependency of the optical properties of water in the bending vibrational band with photo-acoustic measurement

Abstract

Laser-induced acoustic waves have been successfully used for the measurements of dynamic optical properties. We estimated the optical properties of water in the O-H bending vibrational band using the acoustic waves emitted from water irradiated by a tunable mid-infrared Free Electron Laser (MIR-FEL). From these observations, the following results were obtained. (1) The absorption spectrum of water from photo-acoustic measurements was in agreement with that obtained by the FT-IR measurement at room temperature. (2) There was a slight trend in the absorption spectrum below ∼6.1 µm to shift toward longer wavelengths, which is consistent with the previous report on the dynamic optical properties. This technique using longer MIR pulsed-lasers can be used to elucidate the dynamic optical properties of the tissues that depend on the temperature and composition during laser irradiation.