Heterodyned photoacoustic effect generated by irradiation of single particles by two laser beams modulated at different frequencies

Yaqi Zhang; Wenyu Bai; Gerald J Diebold

doi:10.1016/j.ultras.2020.106157

Heterodyned photoacoustic effect generated by irradiation of single particles by two laser beams modulated at different frequencies

Ultrasonics. 2020 Aug:106:106157. doi: 10.1016/j.ultras.2020.106157. Epub 2020 Apr 11.

Authors

Yaqi Zhang¹, Wenyu Bai¹, Gerald J Diebold²

Affiliations

¹ Department of Chemistry, Brown University, Providence, RI 02912, USA.
² Department of Chemistry, Brown University, Providence, RI 02912, USA. Electronic address: Gerald_Diebold@brown.edu.

PMID: 32315836
DOI: 10.1016/j.ultras.2020.106157

Abstract

When a modulated light beam is absorbed by an incompressible particle, the photoacoustic effect can take place through heat diffusion into the surrounding fluid followed by thermal expansion and the generation of sound. When two laser beams modulated at different frequencies irradiate a particle in aqueous solution, the effect of one laser is to modulate the thermal expansion coefficient of the solution in the proximity of the particle at its modulation frequency. Heat diffusion into the same region of fluid from absorption of radiation from the second laser takes place in fluid where the thermal expansion coefficient is modulated so that the photoacoustic effect is produced at the sum and difference frequencies of the two lasers. Here, a theory for the photoacoustic effect at the heterodyne frequency for a single particle and the corresponding experiments with carbon particles of different sizes are reported.

Keywords: Heterodyne measurement; Heterodyned photoacoustic effect; Modulation of thermal expansion coefficient.