Experimental Study of a Millimeter-Sized Ga-In Drop Ablated by a Nanosecond Laser Pulse

The motion of millimeter gallium-indium (Ga-In) drops subject to intense Neodymium-doped Yttrium Aluminum Garnet (Nd: YAG) laser blasts in the air is investigated experimentally. The drop first experiences plasma emissions and then undergoes interfacial instabilities. The effective ablation pulse energy is quantified by the laser-induced shockwave propagation. The laser-blast-induced concave expansion and spanwise depression history is measured, and the data collapse on straight lines with proper rescaling of pulse energy and time. The propulsion speed of the drop is described by a semi-empirical model that considers the laser energy and fluence at the threshold of ablation. The data show that this propulsion speed scaling remains valid to the millimeter drop ablated by the pulsed laser with beam spot much smaller than the drop, although the original scaling was derived and verified for the indium-tin (In-Sn) droplet of tens of micrometers impacted by a laser pulse with the focal point larger than the droplet.