Pulsed-laser induced gold microparticle fragmentation by thermal strain

Laser fragmentation of suspended microparticles (MP-LFL) is an upcoming alternative to laser ab-
lation in liquid (LAL) that allows to streamline the delivery processes and to optimize the irradiation
conditions for best efficiency. Yet, the structural basis of this process is not well understood to date.
Herein we employed ultrafast x-ray scattering upon picosecond laser excitation of a gold microparticle
suspension in order to understand the thermal kinetics as well as structure evolution after fragmen-
tation. The experiments are complemented by simulations according to the two-temperature model
to verify the spatiotemporal temperature distribution. It is found that above a fluence threshold of
750 J/m2 the microparticles are fragmented within a nanosecond into several large pieces where the
driving force is the strain due to a strongly inhomogeneous heat distribution on the one hand and
stress confinement due to ultrafast heating compared to stress propagation on the other hand. An
additional limited formation of small clusters is attributed to photothermal decomposition on the
front side of the microparticles at a fluence of 2700 J/m2.