Controlled-motion of floating macro-objects induced by light

Photons energy can be conventionally converted to mechanical work through a series of energy-expensive steps such as for example delivery and storage. However, these steps can be bypassed obtaining a straightforward conversion of photons energy to mechanical work. As an example, in literature, high power near infrared light is used to move small objects floating on fluid surfaces, exploiting the Marangoni effect. In this work we use a low power non-collimated visible laser-light to induce thermal surface tension gradients, resulting in the movement of objects floating on fluid surfaces. By real time tracking of the object trajectories, we evaluate the average applied driving force caused by the light irradiation. In addition we show how transparent objects can be moved by light when the supporting fluids are properly doped.