  Droplet-droplet interactions is ubiquitous in various applications ranging
from medical diagnostics to enhancing and optimizing liquid jet propulsion. We
employ an experimental technique where the laser pulse interacts with a
micron-sized droplet and causes optical breakdown. The synergy of a nanosecond
laser pulse and an isolated spherical droplet is accurately controlled and
manipulated to influence the deformation and fragmentation of an array of
droplets. We elucidate how the fluid dynamic response (such as drop-drop and
shock-drop interactions) of an arrangement of droplets can be regulated and
optimally shaped by laser pulse energy and its interplay with the optical
density of liquid target. A new butterfly type breakup is revealed, which is
found to result in controlled and efficient fragmentation of the outer droplets
in an array. The spatio-temporal characteristics of a laser-induced breakdown
dictate how shock wave and central droplet fragments can influence outer
droplets. The incident laser energy and pulse width employed in this work are
representative of diverse industrial applications such as surface cleaning,
nano-lithography, microelectronics, and medical procedures such as intraocular
microsurgery.

Fluid Dynamics;Applied Physics