Exact solution for laser-induced thermo-capillary force on a 3D microbubble in a liquid

Abstract

When a laser beam is focused into a volume of highly absorbing thermal medium, gas bubbles can be generated due to the temperature change caused by the laser. In our previous work, it has been shown that these optically generated microbubbles can be steered/manipulated using a low power focused laser beam. Also all possible forces acting on a microbubble which is confined inside a horizontal glass container have been studied and a model is developed to calculate the thermo-capillary force acting on the microbubble. It has been experimentally shown that the microbubble is attracted towards the laser beam due to the thermo-capillary force which is usually larger than the optical force. When developing the complete force model, the thermo-capillary force, optical force, buoyancy force and viscous force have been considered. In our latest work, 2D microbubble trapping is extended to 3D by considering both transversal and axial temperature gradients acting on the microbubble. Microbubbles are generated inside a thick cuvette containing a liquid with absorbing dye through nucleation. Both transversal and axial temperature profiles are calculated by separately solving transversal and axial heat equations and matching the peak temperature change. In this work, the thermo-capillary force on a microbubble is determined by directly solving the 3D heat equation by 3D Fourier transform methods.