Behind optothermal trapping of photothermally-induced microbubbles

We present 3D steady-state trapping and manipulation of vapor microbubbles in pure ethanol by optothermal effects induced by low power CW laser. Light absorption from silver nanoparticles photodeposited on the core of a multi-mode optical fiber is used as a heat source to induce microbubbles of several diameters. The optothermal effects generated by the light absorption of light bulk absorption modulates the microbubble wall's surface tension inducing both longitudinal and transversal forces just like optical forces, generating a 3D potential well. By numerical simulations, we find expressions to describe both the temperature profiles and the convective currents. Besides, using an array of three optical fibers with silver nanoparticles photodeposited on their cores we show the transmission of microbubbles from one fiber to another by switching the laser radiation from the CW lasers.