Sub-threshold laser jetting via flow-focusing with transient meniscus formation *

Increasing the printing resolution of drop-on-demand jet-based printing and deposition techniques is important for many industrial applications. In this study, we present two methods to minimize the jet size and reduce the laser threshold energy of a variant of the laser-induced forward transfer (LIFT) process called blister-actuated LIFT (BA-LIFT). In one method,  we use a magnetic shaker to introduce Faraday waves into the thin liquid film to be printed. At the resonance frequency, the acoustic waves lead to the formation of sinusoidal patterns and a transient meniscus on the liquid film surface.  In the other method, we use laser pulses to create capillary surface waves on the liquid film surface to form a transient meniscus. In both of these cases, a subsequent laser pulse is focused on the substrate at the right time to cause flow-focusing.  We demonstrate experimentally and computationally that transient meniscus formation enables jetting at lower laser pulse energies and leads to the ejection of smaller droplets.