A prelude to the multibeam photoacoustics

Abstract

The research focuses on the introduction and validation of the lock-in photoacoustics of condensed systems in the presence of two simultaneous probing beams. The experiments, performed on three model systems: a perfect absorber - carbon black membrane, a multilayer system - acrylic coated copper plate, and a luminescent sample - ruby, were aimed at the comparative analysis of the frequency domain photoacoustic responses to a single probe beam (classical approach) and to two probe beams (of different wavelength). A modulation frequency shift criterion allowing the simultaneous acquisition of two independent signals was recognized. No synergistic or cross effects of the two-beam excitation on the photoacoustic signal generation (beam intensity effects or modulation frequency effects) were observed. The multibeam photoacoustic data appear to be (at least) equivalent to classically obtained results for stationary systems. It is expected that the multibeam approach will extend the applicability of photothermal methods to time-dependent systems, where the evolution of distinct absorption bands is of particular interest. An application of the developed method, related to the site-dependent energy storage efficiency of photosynthetically active samples, was described and validated on a three-beam experiment performed on a model Ficus benjamina L. leaf.