PULSED-LASER-INDUCED CAVITATION: Ultrafast bubbles enable novel nano/microfluidic systems

摘要

Various fluid delivery and actuation mechanisms on the micro- and nanoscale have been devised using both optical and mechanical methods; now, researchers at the University of California at Los Angeles (UCLA) have demonstrated multiple novel fluidic devices based upon the high speeds, high pressures, and strong forces created by pulsed-laser-driven cavitation bubbles. A high-speed microfluidic switch, a fluorescence-activated cell sorter, and a high-speed droplet-on-demand device are just three of the technologies enabled by this laser-induced effect. When a laser pulse is highly focused in a liquid medium, the laser energy breaks down the molecules in the liquid and generates ionized hot plasma (6000-15,000 K) near the focal point (see figure). On nanosecond time scales, the hot plasma recombines, instantly heats the liquid, and creates an explosive vapor bubble that expands at a speed greater than 100 m/s. Pressure inside the bubble can be as high as tens of megapascals. Triggering these bubbles takes nanoseconds or even femtoseconds depending on the pulse duration.