Dynamics of ring-shaped cavitation bubbles induced by long pulse laser

A novel approach is proposed for coupling the energy of a 2.94μm Long-Pulse Laser(LPL) generated by an Er:YAG laser to a sapphire fiber using a conical lens. This method results in the formation of an annular laser spot distribution at the fiber's output end, which is applied to induce Ring-Shaped Cavitation Bubbles (RSCB) in a thin layer of distilled water. The center of the bubble corresponds to the singularity of the RSCB. Research of the dynamics of the RSCB reveals that these bubbles originate from the merging of multiple independent bubbles, exhibiting a double-layered distribution in the radial direction. Over time, the variation in the outer radius of the RSCB conforms to the classical Rayleigh model, while the singularity radius at the bubble's center remains relatively constant.