Chemical amplification of optoacoustic signals

Abstract

Historically, the optoacoustic effect has been produced in gases through the absorption of IR radiation^1–3. As the effect depends only on the conversion of modulated radiation to periodic heating of the gas (which in a closed vessel is equivalent to a sound wave), it is not surprising that the optoacoustic effect can be produced by several different interactions where radiation is absorbed by matter. Here we report generation of the optoacoustic effect by photochemical release of energy through a chain reaction mechanism in H₂–Cl₂ mixtures. A unique feature of the optoacoustic effect produced in this manner is chemical amplification of the acoustic signal caused by a release of energy from the chemical reactions that is greater than the energy absorbed from the light beam. In addition, because the acoustic signal depends on the kinetics of the reaction and the time dependent concentrations of the reactants, the optoacoustic effect acts to monitor directly the progress of the reaction in time.