Pulsed-laser induced gold microparticle fragmentation by thermal strain

Laser fragmentation of suspended microparticles (MP-LFL) is an upcoming alternative to laser ablation in liquid (LAL) that allows the delivery processes to be streamlined and the irradiation conditions to be optimized for superior efficiency. However, 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 fragmentation. 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 m^-2 the microparticles are fragmented within a nanosecond into several large pieces where the driving force is the strain due to strongly inhomogeneous heat distribution on the one hand and stress confinement due to ultrafast heating compared to stress propagation on the other hand. In addition, limited formation of small clusters is attributed to photothermal decomposition on the front side of the microparticles at a fluence of 2700 J m^-2.