Droplet deformation by short laser-induced pressure pulses

Abstract

(Received xx; revised xx; accepted xx)When a free-falling liquid droplet is hit by a laser it experiences a strong ablation driven pressure pulse. Here we study the resulting droplet deformation in the regime where the ablation pressure duration is short, i.e. comparable to the time scale on which pressure waves travel through the droplet. To this end an acoustic analytic model for the pressure-, pressure impulse-and velocity fields inside the droplet is developed in the limit of small density fluctuations. This model is used to examine how the droplet deformation depends on the pressure pulse duration while the total momentum to the droplet is kept constant. Within the limits of this analytic model, we demonstrate that when the total momentum transferred to the droplet is small the droplet shape-evolution is indistinguishable from an incompressible droplet deformation. However, when the momentum transfer is increased the droplet response is strongly affected by the pulse duration. In this later regime, compressed flow regimes alter the droplet shape evolution considerably.

Mass Loss from a Stretching Semitransparent Sheet of Liquid Tin

“…2. These features may be caused by jetting and bursting, phenomena that could originate from laser-induced cavitation inside the liquid [14,15,23]. The amount of mass contained in these features is expected to be small [15].…”

“…Such debris could limit the lifetime of nearby light-collection optics [4,[6][7][8][9]. Several recent studies have provided insight into the response of a tin microdroplet to a nanosecond laser pulse in which the propulsion [10,11] accompanies a deformation [10][11][12][13][14] of the droplet into a thin sheet. The eventual breakup and fragmentation of the sheet into much smaller droplets has also been studied [9,15].…”

“…[16,17]. Droplet deformation and fragmentation upon impact, be it onto a solid substrate or by a laser pulse, is a topic of particular current interest in fields ranging from epidemiology, governing the transport of pathogens from sneezes and coughs [17,18], through sprays relevant in, e.g., agriculture [18,19], to state-of-the-art nanolithography [7,[10][11][12][13][14]. Knowledge of the thickness profile of the thin liquid sheet formed upon impact is crucial for understanding the deformation and complex fragmentation processes involved.…”

Smoothed particle hydrodynamics simulation of a laser pulse impact onto a liquid metal droplet

“…In comparison to DUV lithography, where the wafer is surrounded by air, in the EUV lithography the laser operates in a large vacuum chamber. Another difference is that in EUV the liquid metal droplets are deformed due to two stages of laser impact [ 6 – 8 ].…”

“…In a follow up work, Gelderblom et al [ 31 ] studied a free falling water drop hit by a nanosecond laser pulse and investigated the effect of the pulse shape and the droplet properties on its deformation. More recently, Reijers et al [ 8 ] modelled the droplet deformation for short ablation pressure duration. They found that for small transfer of momentum the shape of the droplet resembles of an incompressible droplet deformation.…”