Light moves macro-objects

摘要: 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.In order to study the light induced motion of small objects on fluids [1–5] we performed a series of experiments by using an experimental setup based on an Argon Ion cw laser impinging on a small cork disc floating on three different fluids: water, ethanol and a solution of ethanol and an azo-dye whose absorption spectrum is centered around the blue wavelength of λ= 476. 5 nm used to irradiate the cork. Fig. 1 shows the steps of the irradiation process at different time intervals when a small cork disk, whose diameter is 5mm thickness 2mm and mass m= 0. 058g, floats on ethanol. As it is shown in Fig. 1 (a), at the beginning of irradiation the cork disc is partially heated by light in order to induce the thermal gradient necessary to …