The photoacoustic effect generated by an incompressible sphere

Abstract

An incompressible sphere with a vanishing thermal expansivity suspended in a fluid can generate a photoacoustic effect when the heat deposited in the sphere by a light beam diffuses into the surrounding liquid causing it to expand and launch a sound wave. The properties of the photoacoustic effect for the sphere are found using a Green's function solution to the wave equation for pressure with Neumann boundary conditions. The results of the calculation show that the acoustic wave for fast heat liberation is an outgoing compressive pulse followed by a reflected pulse whose time profile is modified as a result of frequency dependent reflection from the sphere. For slow heat release by the sphere, the photoacoustic effect is shown to be proportional to the first time derivative of the heat flux at the particle-fluid interface.

Optoacoustic characterization of prostate cancer in anin vivotransgenic murine model

“…The results may arise from the principle that the amplitude of the OA signal is largely affected by the optical absorption of the target (determined by, e.g., blood vessel size, oxygenation status), while the frequency component may be more related to the geometrical properties of absorbing structures (e.g., blood vessel size, oxygenation status, and spatial distribution). 32 Our imaging approach of integrating OA signals within a 3 μs time window and projecting these values onto a 2-D plane yielded OA images with tumor contrast of 31 to 36 dB. The OA predicted dimensions agree with the true dimensions to within 0.5 mm.…”

“…8,29,31 RF data are collected in OA imaging wherein the size of the absorbing structure contributes to the frequency content of the OA signal. 32 Spectrum analysis of RF OA signals generated by blood vessel phantoms (cylindrical tubes filled with ink and embedded into gelatin) shows a relationship between the spectral components and the diameter of the cylinders. 33 Spectrum analysis of high-frequency OA signals from ex vivo ocular tissue has also shown changes in the midband fit and slope around the pigmented iris.…”

Photoacoustic transients produced by laser generated, ultrahigh thermal gradients

“…Equation (1) has been used to describe the directional properties and characteristic waveforms of photoacoustic waves for numerous applications including those generated by laser beams directed into absorbing liquids, 3,7,8 optically thin bodies with simple geometries such as spheres, cylinders, and layers, [9][10][11][12] fluids with spatially symmetric absorbances, 13 and waves produced by irradiation of biological tissue. 14 Of further note is that in imaging based on the photoacoustic effect, 14 algorithms to determine the spatial dependence of H, given the pressure profile, are based on inversion of Eq.…”

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“…2(a) at t = 200. The photoacoustic signal generated by an incompressible sphere can be understood by the theory discussed in [16]. Furthermore, to compare the profile difference between the traces in Figs.…”