Contactless photoacoustic imaging of biological samples

In this paper we report on remote photoacoustic imaging using an interferometric technique. By utilizing a twowave mixing interferometer ultrasonic displacements are measured without any physical contact to the sample. This technique allows measurement of the displacements also on rough surfaces. Mixing a plane reference beam with the speckled beam originating from the sample surface is done in a Bi ₁₂SiO ₂₀ photorefractive crystal. After data acquisition the structure of the specimen is reconstructed using a Fourier-domain synthetic focusing aperture technique. We show three-dimensional imaging on tissue-mimicking phantoms and biological samples. Furthermore, we show remote photoacoustic measurements on a human forearm in-vivo.