A schematic view shows a microbubble implosion, depicting the laser illumination, hot electron spread, implosion, and proton flash. (Credit: M. Murakami)

Scientists at Osaka University (Osaka, Japan) have discovered a novel particle acceleration mechanism called microbubble implosion, in which extremely high-energy hydrogen ions (in other words, protons traveling at relativistic speeds) are emitted at the moment when ultrafast-laser-produced microbubbles in hydrides (hydrogen-contaning materials) shrink to atomic size.1

Led by Masakatsu Murakami, the group has reported an astonishing (simulated) physical phenomenon: when matter is compressed via the microbubble effect, creating densities comparable to matter the size of a sugar cube weighing more than 100 kg (a compression ratio higher than that for current inertial-confinement fusion experiments), high-energy protons are emitted from positively charged nanoscale clusters. Conventionally, an acceleration distance of several tens to hundreds of meters is necessary for conventional accelerators to generate such high proton energies.