  A free-falling absorbing liquid drop hit by a nanosecond laser-pulse
experiences a strong recoil-pressure kick. As a consequence, the drop propels
forward and deforms into a thin sheet which eventually fragments. We study how
the drop deformation depends on the pulse shape and drop properties. We first
derive the velocity field inside the drop on the timescale of the pressure
pulse, when the drop is still spherical. This yields the kinetic-energy
partition inside the drop, which precisely measures the deformation rate with
respect to the propulsion rate, before surface tension comes into play. On the
timescale where surface tension is important the drop has evolved into a thin
sheet. Its expansion dynamics is described with a slender-slope model, which
uses the impulsive energy-partition as an initial condition. Completed with
boundary integral simulations, this two-stage model explains the entire drop
dynamics and its dependance on the pulse shape: for a given propulsion, a
tightly focused pulse results in a thin curved sheet which maximizes the
lateral expansion, while a uniform illumination yields a smaller expansion but
a flat symmetric sheet, in good agreement with experimental observations.
