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Updated: Mar 25, 2026

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere
Published on: April 30, 2018
Motion of Optically Heated Spheres at the Water-Air Interface
A Girot1,2, N Danné1,2, A Würger2
1Université de Bordeaux , Centre de recherche Paul-Pascal (CRPP), 33600 Pessac, France.
Abstract:
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.
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