Drop fragmentation by laser-pulse impact

Abstract

We study the fragmentation of a liquid drop that is hit by a laser pulse. The drop expands into a thin sheet that breaks by the radial expulsion of ligaments from its rim and the nucleation and growth of holes on the sheet. By combining experimental data from two liquid systems with vastly different time-and length scales we show how the early-time laser-matter interaction affects the late-time fragmentation. We identify two Rayleigh-Taylor instabilities of different origins as the prime cause of the fragmentation and derive scaling laws for the characteristic breakup time and wavenumber. The final web of ligaments results from a subtle interplay between these instabilities and deterministic modulations of the local sheet thickness, which originate from the drop deformation dynamics and spatial variations in the laser-beam profile.

Mass Loss from a Stretching Semitransparent Sheet of Liquid Tin

“…At later times, many holes quickly appear and obstruct the analysis. Time τ * has previously been observed to decrease with the Weber number We = ρR 0 U 2 /σ as τ * /τ c ∼ We −1 [15]. Thus, with an increasing Weber number, the thickness is probed by the TC method at earlier times.…”

“…1(a1.2), 1(a2.2), and 1(a3.2), we observe ripples. These ripples are the signature of a fluid-dynamic instability that will eventually puncture the sheet and cause the formation of holes [15,25]. On uniform sheets, these holes open at a constant Taylor-Culick (TC) speed [22],…”

“…Holes appearing near the edge of the sheet cannot be used in the TC method due to significant nonuniformity of the local thickness profile [15]. In addition, the edge curvature distorts the hole overlay close to the sheet circumference.…”

“…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]. The thickness evolution of expanding sheets formed by the impact of millimetersized water drops onto a pillar has been investigated in Refs.…”

“…However, to date no experimental data are available on the thickness profile of the stretching nanometric liquid metal sheet formed after laser impact. Several theoretical models have been suggested [13,17,20] and applied to tin microdroplets [15] but it has not yet been possible to draw any clear conclusions regarding the thickness profile. Obtaining such information would enable us to estimate how much tin mass is actually retained in the expanding target sheet when it is hit by the main laser pulse in plasma sources of EUV light.…”