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The photoinduced motion of an oil droplet on an aqueous solution under local irradiation by a green laser is reported. The results showed that a repulsive force is generated on pure water, while an attractive force is observed with an aqueous solution containing a surfactant. The driving force is discussed in terms of a thermal Marangoni effect. The switching on the photothermal effect is interpreted by taking into account the advection caused by the spatial gradient of the surface tension under local heating by a laser. A numerical model revealed that the geometrical profile of the surface tension around the droplet determines the mode of advection around the droplet and causes switching in the direction of migrations.

Directed motion of an oil droplet floating in an aqueous solution is generated by using a laser beam. Interestingly, the direction of the droplet motion can be switched between forward and backward by changing the optical path of the laser through the droplet. This motion is caused above a certain critical power of the laser, and above this value the velocity increases almost linearly with the power. The mechanism of this directed motion is explained as follows: the oil droplet is locally heated by a narrow laser beam, this local heating induces a specific mode of convection inside the droplet, and this generated convective motion produces translational directed motion of the droplet.

Rhythmic bursting on the order of seconds in a cluster of plastic beads under continuous irradiation of a focused neodymium-doped yttrium aluminum garnet (Nd:YAG) laser beam (1064 nm) is reported. The oscillatory instability is induced as a result of competition between trapping and scattering forces, where both forces are induced by the focused laser beam. Above a critical power of the laser beam, mode bifurcation from the stationary state into periodic bursting is observed. Our model employing ordinary differential equations reproduces the essential aspects of the experimental results.