本文利用Q開關脈衝式雷射聚焦於自由水平面下，並且改變聚焦點離水面的深度，觀察水面上的喷濺之形成與時間演進的結構變化。水面上的喷濺水柱有粗細兩段，然後粗水柱的頂部有一個皇冠結構的喷濺。此皇冠喷濺由特殊環狀水面塌陷的回復所產生。在時間的演進中，我們發現皇冠喷濺會漸漸收縮閉合產生氣泡於粗水柱之中，並在適當的聚焦深度下，此氣泡中還會包覆一顆小水滴。

The dynamics of a water jet on a flat free surface are investigated using a nanosecond pulsed laser for creating an oscillating bubble with different depths beneath the free surface. The water jet shows a thin jet followed by a markedly thicker jet and a circular crown-like jet perfectly connected on the shoulder of the thick jet transited to the thin jet. The crown-like jet is generated from the collapse of a circular ring-shaped crater. In the temporal evolution of the water jet, we find an intriguing pattern formation that the crown-like jet gradually closes and finally forms an air bubble. For certain depth, the air bubble perfectly encloses a water drop through the process of Plateau-Rayleigh instability.