Thermocapillary Convective Flows Generated by Laser Points or Patterns: Comparison for the Noncontact Micromanipulation of Particles at the Interface

This letter compares the controlled manipulation of micrometer size particles using thermocapillary convective flows generated by laser points or patterns. Such flows are generated when a surface tension stress is generated at the fluid/gas interface due to a thermal gradient. Laser heating allows to generate fast, localized flows that are used to displace a particle towards a desired position. However, these flows are repulsive and so the system is unstable. Although using the simple laser spot with a closed-loop control enables to control the particle displacement, the control of the particle movement direction is somehow difficult and the particle position stabilization remains challenging. In this letter, it is proposed to use laser patterns to overcome these limitations. Experimental tests are performed using a 500-$\mu$m-diameter steel spherical particle that is displaced towards a target position. The preliminary experimental results show that it is possible to overcome the above mentioned limitations while still obtaining maximal particle velocities ranging from 4 to 9 mm/s during the displacement phase.