Motion of Optically Heated Spheres at the Water-Air Interface

A. Girot, N. Danné, A. Würger, T. Bickel, F. Ren, J. C. Loudet, B. Pouligny*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


A micrometer-sized spherical particle classically equilibrates at the water-air interface in partial wetting configuration, causing about no deformation to the interface. In condition of thermal equilibrium, the particle just undergoes faint Brownian motion, well visible under a microscope. We report experimental observations when the particle is made of a light-absorbing material and is heated up by a vertical laser beam. We show that, at small laser power, the particle is trapped in on-axis configuration, similarly to 2-dimensional trapping of a transparent sphere by optical forces. Conversely, on-axis trapping becomes unstable at higher power. The particle escapes off the laser axis and starts orbiting around the axis. We show that the laser-heated particle behaves as a microswimmer with velocities on the order of several 100 μm/s with just a few milliwatts of laser power.

Original languageEnglish
Pages (from-to)2687-2697
Number of pages11
Issue number11
Publication statusPublished - 29 Mar 2016
Externally publishedYes


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