Focusing by use of time reversal of photoacoustic waves

Time reversal of ultrasonic waves allows focusing of ultrasound through complex media, such as highly aberrating media. On one hand, focusing with time reversal can be performed by backpropagating detected ultrasonic waves generated by a localized ultrasound source. This source classically consists of high acoustic contrasts echoing ultrasonic waves generated by an incident ultrasonic field, or directly by pointlike transducers inserted in the medium. On the other hand, the photoacoustic effect consists of the emission of ultrasound caused by the absorption of light by an optical absorber. In particular, this effect can be used to ultrasonically image a distribution of optical absorbers simply by recording photoacoustic signals on an imaging transducers array. In this work, we perform time reversal of ultrasound generated by a pointlike photoacoustic source in order to automatically focus ultrasound back to an optical contrast. A Q‐switched pulsed Nd:YAG laser was used to illuminate tissue phantom with na...