Photoacoustic generation of focused ultrasonic pulses with predefined temporal profiles including quasi-unipolar pressure pulses

Abstract

One of the applications of the photoacoustic effect in biomedical research is generation of ultra-short acoustic pressure pulses in tissue. An acoustic wave is generated directly in tissue or in an acoustically well coupled immersion liquid, thus avoiding mechanical resonances of the piezoelectric ultrasonic transducer. Although laser generation of the unipolar pressure pulses has been proposed and used before, little attention was paid to the change of the temporal shape of the pulse when it propagates from a transducer. Here we derive simple mathematical solution which helps to predict the pulse shape in the focal region of the transducer and to experimentally verify theoretical calculations showing generation of short quasi-unipolar pressure pulses.