Nucleation dynamics around single microabsorbers in water heated by nanosecond laser irradiation

Suspensions containing micro- and nanoabsorbers, which are irradiated by short laser pulses, are used for a manifold of procedures in medicine, biotechnology, and other fields. Detailed knowledge of the bubble nucleation and dynamics, which is induced by the heat transfer from the absorber to the surrounding transparent water, is essential for understanding the underlying processes occurring on a microscopic scale. We investigated the rapid phase change phenomena including temperature, heating rates, pressure generation, bubble nucleation, and initial bubble growth around absorbing micron-sized melanin particles (retinal pigment epithelial melanosomes) during irradiation with 12 ns (full width at half maximum) laser pulses at a wavelength of 532 nm. The melanosomes were heated at rates in the order of 1010 Ks. A mean bubble nucleation temperature of 136 °C was found. The initial bubble expansion was observed by time-resolved microscopy. The expansion velocities range from 10 ms at 1.5-fold to 85 ms at 8.5-fold threshold radiant exposure for bubble formation, respectively. The expansion velocity increases in the investigated range almost linearly with the applied radiant exposure.