Discharge-bubble luminescence

When a bubble in a liquid collapses, the gas inside it can get compressed and heated to the point that it spontaneously ionizes. The resulting plasma is short-lived, and when its atoms recombine it gives off a flash of light. (See Physics Today, April 2012, page 18, and the article by Detlef Lohse, Physics Today, February 2003, page 36.) The process was first studied using ultrasound-generated bubbles some 10–100 µm in size that lasted tens of microseconds; the picosecond light bursts from the collapsing bubbles earned the moniker sonoluminescence. Dielectric breakdown at the focus of a pulsed laser can also induce bubbles—an order of magnitude larger and lasting an order of magnitude longer than the acoustic bubbles, with flashes lasting nanoseconds. A new paper by Keping Yan and colleagues at China’s Zhejiang University examines a more recent source of luminescing bubbles: electric discharge. Connecting an underwater...