3D trapping of thermally generated microbubbles

Nonlinear absorption of laser radiation focused on a volume of a highly absorbing thermal medium creates a temperature difference and induces a refractive index change inside the medium. It has been shown that gas bubbles can be generated by increasing the focused laser power due to thermal blooming. In our previous work, all possible forces acting on a microbubble which is confined within a horizontally oriented thin glass container have been incorporated in the force model. The thermo-capillary force is the dominant attractive force, while the optical force is repulsive. It is experimentally shown that the microbubble can thus be trapped by a focused laser beam and they can be manipulated by steering the laser beam. In this work, the 2D trapping is extended to 3D by generating a microbubble inside a vertical thick glass cuvette. A 514.5 𝑛𝑚, Ar-ion laser beam, tightly focused using a microscope objective, is used to generate and trap the microbubble. Once again, the force model is developed: unlike the 2D case, there are no contributions from surface tension and friction.