Three-dimensional bubble channel based on a photothermal field by a multiphoton process

Abstract New techniques for accurately controlling microbubble positioning, leveraging the three-dimensional and high spatial resolution of two-photon absorption, have been experimentally demonstrated. Femtosecond laser pulses focused on a solution created a sharp thermal gradient at the focal point, where Marangoni forces acting on the trapped bubbles exceeded 380 pN, considerably stronger than those generated by thermal diffusion. This effect was used to position bubbles with micrometer accuracy along a narrow two-photon absorption distribution with a length of 1 mm. The novel bubble and flow driving principles, combined with fast and precise energy distribution control techniques in optics, provide innovative proposals for microfluidics, soft robotics, and many other fields.