Pulsed optoacoustic spectroscopy of condensed matter

Abstract

The authors discuss the theory and experiments dealing with the pulsed optoacoustic effect (i.e., generation of a transient acoustic wave by absorption of an optical pulse) in condensed matter. Their primary interest lies in the measurement of small absorption coefficients (10-1 cm-1). At present an experimental capability of measuring absorption coefficients as small as 10-6 cm-1 has been demonstrated, and further improvement is foreseen. The pulsed optoacoustic absorption measurement technique has been applied to the following linear spectroscopic studies: (1) precise measurements of the optical absorption spectra of H2O and D2O; (b) accurate determination of absorption strengths and profiles of high harmonics (n=6,7 and 8) of vibrational modes in transparent organic liquids (e.g., benzene); (c) quantitative absorption spectra of thin (∼ 1-10 μm) liquid films; and (d) quantitative absorption spectra of solids and finely powdered crystals. The usefulness of the pulsed optoacoustic technique to nonlinear spectroscopy has been demonstrated in the following studies: (a) quantitative two-photon absorption spectroscopy of the weak two-photon (B2μ1A1g1) transition in benzene; and (b) optoacoustic Raman-gain spectra for a variety of liquids where an ability to measure Raman gains as small as 10-5 cm-1 has been demonstrated. In addition to reviewing the above studies the authors discuss future possible applications and compare the pulsed optoacoustic spectroscopy technique with other optoacoustic absorption measurement techniques. © 1981 American Physical Society.