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We study numerically the deformation of sessile dielectric drops immersed ina second fluid when submitted to the optical radiation pressure of a continuousGaussian laser wave. Both drop stretching and drop squeezing are investigatedat steady state where capillary effects balance the optical radiation pressure.A boundary integral method is implemented to solve the axisymmetric Stokes flowin the two fluids. In the stretching case, we find that the drop shape goesfrom prolate to near-conical for increasing optical radiation pressure whateverthe drop to beam radius ratio and the refractive index contrast between the twofluids. The semi-angle of the cone at equilibrium decreases with the drop tobeam radius ratio and is weakly influenced by the index contrast. Above athreshold value of the radiation pressure, these "optical cones" becomeunstable and a disruption is observed. Conversely, when optically squeezed, thedrop shifts from an oblate to a concave shape leading to the formation of astable "optical torus". These findings extend the electrohydrodynamics approachof drop deformation to the much less investigated "optical domain" and revealthe openings offered by laser waves to actively manipulate droplets at themicrometer scale.

Stretching and squeezing of sessile dielectric drops by the optical radiation pressure