Time-resolved Study of Laser-induced Bubbles and Shockwaves in Agar Gel Tissue Phantoms

INTRODUCTION Laser-tissue interactions have been extensively used in a number of biomedical treatments. However, the high optical absorption in tissue and the use of relatively long laser pulses or, in many cases, cw laser exposure, frequently results in excessive laser-heating producing undesirable collateral damage. Short pulsed lasers are one of the most precise tools for delivering energy and can allow for the greatest finesse [1]. Laser pulses with duration of only a few nanoseconds, and as short as a few hundreds of femtoseconds, seem to be a good alternative to minimize or even suppress laser-heating undesirable effects [2]. This work presents a time-resolved study of the interaction of short laser pulses with agar gel tissue phantoms. By using a pumpprobe laser system, the phenomenon of laser-induced bubble formation in the agar gel is optically imaged onto a CCD; the design of the experimental set up allows us to record both the launching and the propagation of the shockwave that is the precursor to the bubble expansion. Laser-induced bubble formation and acoustic/shock wave propagation have been extensively investigated in water, whereas very few studies incorporate biological tissues or even tissue models such as agar gels [3,4].