Optoacoustic imaging:

Example of pressure wave generation

Steven L. Jacques, Guenther Paltauf

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As an illustration, consider the pressure and velocity potential as a function of time observed at the center of a 1-mm-diameter sphere in which 10 J/cm3 is deposited at time zero. The surrounding medium has not energy deposition.

The pressure within the sphere is uniform at time zero, so the detector sees a constant pressure of (10 J/cm3)(Γ = 0.12)(10 bar/(J/cm3)) = 12 bar or 1.2x106 Pa.
The velocity potential is a linear slope and the pressure is prorportional to that slope. Once the pressure release from the edge of the sphere reaches the center detector, the velocity potential drops suddenly to zero and the pressure undergoes a negative impulse.

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