Stretching and squeezing of sessile dielectric drops by the optical radiation pressureReport as inadecuate

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1 CPMOH - Centre de physique moléculaire optique et hertzienne 2 TREFLE - Transferts, écoulements, fluides, énergétique

Abstract : We study numerically the deformation of sessile dielectric drops immersed in a second fluid when submitted to the optical radiation pressure of a continuous Gaussian laser wave. Both drop stretching and drop squeezing are investigated at steady state where capillary effects balance the optical radiation pressure. A boundary integral method is implemented to solve the axisymmetric Stokes flow in the two fluids. In the stretching case, we find that the drop shape goes from prolate to near-conical for increasing optical radiation pressure whatever the drop to beam radius ratio and the refractive index contrast between the two fluids. The semi-angle of the cone at equilibrium decreases with the drop to beam radius ratio and is weakly influenced by the index contrast. Above a threshold value of the radiation pressure, these ``optical cones- become unstable and a disruption is observed. Conversely, when optically squeezed, the drop shifts from an oblate to a concave shape leading to the formation of a stable ``optical torus-. These findings extend the electrohydrodynamics approach of drop deformation to the much less investigated -optical domain- and reveal the openings offered by laser waves to actively manipulate droplets at the micrometer scale.

Keywords : Opto-hydrodynamics Radiation pressure laser interface capillarity drop deformation

Author: Hamza Chraibi - Didier Lasseux - Eric Arquis - Régis Wunenburger - Jean-Pierre Delville -



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