Light moves macro-objects

Photons energy can be conventionally converted into mechanical work through a series of energy expensive steps. It has been shown how some of these steps can be bypassed obtaining a direct conversion of photons energy into mechanical work. The most common way consists of using light in the visible or near infrared to move small objects floating on fluid surfaces exploiting the Marangoni effect. In this work we use a low power visible light source to induce a thermal surface tension gradient thus moving a floating object on a fluid surface. By real time tracking of the object trajectory we can determine some physical properties related to the floating object and to the supporting fluid. Moreover from the experimental data fitting we can evaluate the applied driving force due to light irradiation and object heating. In addition we show how even transparent object can be moved by light when the supporting fluid is properly doped.