Billiards With Light

A team headed by LMU physicists is revolutionizing the laser-driven acceleration of protons through tiny plastic spheres. The generated proton beams have unique properties that can benefit future applications.

A team headed by physicists at the LMU has sent laser pulses on tiny plastic spheres. Through this interaction, they accelerated part of the beads almost at the speed of light. The proton beam produced differs fundamentally from the rays previously produced with foils: it has a much greater density of particles. The researchers are currently reporting on this in the journal Nature Communications .

A new development in accelerator technology is laser-driven plasma accelerators. In doing so, electrons or protons are brought to nearly the speed of light with the help of powerful lasers. The source of the protons is usually a thin film that is bombarded with a strong laser pulse. Physicists at the LMU have now replaced this film with floating plastic beads. The diameter of these balls is only one millionth of a meter. The microspheres are so small that you can neither hang them up nor spit them. The researchers levitated the spheres with high precision. The required equipment was developed at the Department of Medical Physics at LMU.

"Simplified, you can imagine the experiment as in billiard, where one sphere consists of light and the other represents our microscopically small floating sphere," explains Peter Hilz , the head of the experiment. The new proton beams will enable experiments that were previously considered impractical.