A Table-Top Path to the Schwinger Limit Using a Plasma Mirror

The Schwinger limit—the field strength at which empty space becomes unstable and spontaneously creates electron-positron pairs—has been sitting out of reach for seventy years. Today's best petawatt lasers are still a million times too weak when focused in the usual way. This paper outlines a table-top concept that tries to close that gap not by building a bigger laser, but by making the laser pulse much shorter and focusing it much tighter with the help of a dense plasma focus. The pinch from that device acts as a mirror that moves at nearly the speed of light, compressing the laser pulse into a train of attosecond X-ray bursts. Those bursts are then focused with multilayer mirrors to a nanometer-sized spot, where the intensity finally enters Schwinger territory. The whole system combines a liquid-metal-anode plasma focus, a commercial petawatt laser, and a compact positron detector. If it works, it would be the first time anyone has seen matter born directly from the vacuum in a laboratory.