Time reversal of photoacoustic waves

In this work, the authors use the photoacoustic effect to create a source for ultrasonic time-reversal experiments. Photoacoustic waves were generated by an optically absorbing gel sphere excited by a laser pulse in a highly optically diffusive solution and recorded with an ultrasound array controlled by a time-reversal electronics. The emission of the time-reversed photoacoustic waves allowed the refocusing of the ultrasound towards the optical absorber, in particular, in the presence of a strongly acoustically defocusing medium. The authors illustrate how the technique can be applied to perform acoustical imaging in the presence of a strong acoustical aberration. (c) 2006 American Institute of Physics.