Spray and microjets produced by focusing a laser pulse into a hemispherical drop

Thoroddsen, Sigurður T.; Takehara, Kohsei; Etoh, T. G.; Ohl, Claus‐Dieter

doi:10.1063/1.3253394

Cited by 90 publications

(68 citation statements)

References 47 publications

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“…Focused nanosecond pulses have for instance been used to induce cavitation in liquids confined in capillary tubes (Vogel et al 1996;Sun et al 2009;Tagawa et al 2012), or jetting and spraying in sessile drops (Thoroddsen et al 2009). These situations involving a liquid close to a wall result in localized flows.…”

Section: Introductionmentioning

confidence: 99%

Drop deformation by laser-pulse impact

et al. 2016

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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. IntroductionA laser pulse interacting with an absorbing liquid body can deposit a finite amount of energy, concentrated both in time and space, which eventually triggers a dramatic hydrodynamic response. Focused nanosecond pulses have for instance been used to induce cavitation in liquids confined in capillary tubes (Vogel et al. 1996;Sun et al. 2009;Tagawa et al. 2012), or jetting and spraying in sessile drops (Thoroddsen et al. 2009). These situations involving a liquid close to a wall result in localized flows. By contrast, we consider here the situation of a mobile liquid body: the impact of a nanosecond laser pulse onto an absorbing unconfined liquid drop, which, as first described by Klein et al. (2015), has a global hydrodynamic response to the pulse: the drop propels forward at a speed of several meters per second, strongly deforms and eventually fragments (see Fig. 1). This dynamics is similar to that following a mechanical impact such as on a solid substrate or a pillar, which has been studied thoroughly (see e.g. Clanet et al. 2004;Yarin 2006;Villermaux & Bossa 2011;Kolinski et al. 2012;Riboux & Gordillo 2014;Josserand & Thoroddsen 2016), including a few studies on the fragmentation of the drop (Villermaux 2007;Xu et al. 2007;Villermaux & Bossa 2009, 2011Riboux & Gordillo 2014). A laser proves to be an adequate tool to vary the extension of the impact without arXiv:1512.02415v1 [physics.flu-dyn] 8 Dec 2015

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Section: Introductionmentioning

confidence: 99%

Drop deformation by laser-pulse impact

et al. 2016

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“…According to [6,25,26,31] the laser beam may induce electrostriction in the water droplet which leads to the formation of a bulge.…”

Section: -7mentioning

confidence: 99%

“…According to [6], such a formation is produced as a function of the deepness of the actual position of the focus inside the droplet which should be of the order of some tens of micrometers. This could be the case in our experiments although the conditions of experiments in [6] are largely different from our experimental conditions. The formation of such a crown could be due to the light pressure exerted by the more divergent rays in the focus (distributed at the periphery of the focus spot) on water.…”

Section: -7mentioning

confidence: 99%

“…The interaction with the optical radiation takes place by transmission of the laser beams through the support surface [6]. In other cases the droplets are produced and fixed or moved within microchannel structures that are designed for their manipulation by light in single-or two -phase flows, in view of their further use in optical chips [7,8].…”

Section: Introductionmentioning

confidence: 99%

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Unresonant interaction of laser beams with microdroplets

Pascu¹,

Popescu²,

Ticoş³

et al. 2012

JEOS:RP

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The interaction of distilled water droplets (volumes of 3-4 µl) with pulsed laser beams emitted at 532 nm is described. At 532 nm the distilled water absorption is very low and the interaction of a water droplet with the laser radiation is dominated by unresonant phenomena. In this case, following the collision of the laser beam with a droplet in suspended position in air, its deformations and mechanical vibrations are produced. The conditions in which the droplets lose material as a consequence of the impact with laser beams are explored. The effects produced on the droplet were studied pulse by pulse and depend on: droplet's content, beam wavelength, power and focusing, irradiation geometry and adhesion of the droplet to the capillary on which it is suspended. The laser pulses energies were varied in four steps: 0.25 mJ, 0.4 mJ, 0.7 mJ and 1 mJ. The laser pulse full time width at half maximum was 5ns and the typical beam waist diameter on the droplet was 90 µm; the beam had a relatively low divergence around the focus point. The droplet's shapes evolution is visualised by recordings performed at 10 kframes/second. Following a droplet interaction with the laser beam one may also produce at a controlled moment in time, nanodroplets propagating at high (probably supersonic) speeds and microdroplets propagating at slower speeds. One may also produce suspended droplets of smaller dimensions than the initial one as well as micro/nano gas bubbles in the suspended droplet's material/volume. In a second set of experiments the behaviour of the microdroplets of Rhodamine 6G in distilled water was recorded at high speed, at resonant interaction with similar laser pulses, and at the same power levels. The phenomena considering that the droplets contents are Newtonian liquids produced at interaction with the laser beams, are discussed.

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“…Liquid buckling is not limited to large viscosities but can appear for water if the compression rate is rapid enough, as occurs during the collapse of cylindrical crowns in sphere impacts [27] and laser ablation [28].…”

Section: Introductionmentioning

confidence: 99%

Vortex-induced buckling of a viscous drop impacting a pool

Beilharz

Thoroddsen

2017

Phys. Rev. Fluids

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CitationLi EQ, Beilharz D, Thoroddsen ST (2017) We study the intricate buckling patterns which can form when a viscous drop impacts a much lower viscosity miscible pool. The drop enters the pool by its impact inertia, flattens, and sinks by its own weight while stretching into a hemispheric bowl. Upward motion along the outer bottom surface of this bowl produces a vortical boundary layer which separates along its top and rolls up into a vortex ring. The vorticity is therefore produced in a fundamentally different way than for a drop impacting a pool of the same liquid. The vortex ring subsequently advects into the bowl, thereby stretching the drop liquid into ever thinner sheets, reaching the micron level. The rotating motion around the vortex pulls in folds to form multiple windings of double-walled toroidal viscous sheets. The axisymmetric velocity field thereby stretches the drop liquid into progressively finer sheets, which are susceptible to both axial and azimuthal compression-induced buckling. The azimuthal buckling of the sheets tends to occur on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution of the vortex ring. The total interfacial area between the drop and the pool liquid can grow over 40-fold during the first 50 ms after impact. Increasing pool viscosity shows entrapment of a large bubble on top of the drop, while lowering the drop viscosity produces intricate buckled shapes, appearing at the earliest stage and being promoted by the crater motions. We also present an image collage of the most intriguing and convoluted structures observed. Finally, a simple point-vortex model reproduces some features from the experiments and shows variable stretching along the wrapping sheets.

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Spray and microjets produced by focusing a laser pulse into a hemispherical drop

Cited by 90 publications

References 47 publications

Drop deformation by laser-pulse impact

Drop deformation by laser-pulse impact

Unresonant interaction of laser beams with microdroplets

Vortex-induced buckling of a viscous drop impacting a pool

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