Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR; Dresden, Germany) directed light from the Dresden Laser Acceleration Source (DRACO), a terawatt laser (which equals one trillion watts), perpendicularly and obliquely onto a thin metal foil, allowing them to demonstrate for the first time that accelerated protons follow the direction of the laser light. The work yielded unprecedented high proton energies, which could be promising for cancer therapy.1
A light pulse coming from the DRACO laser—which currently reaches a peak power of 150 TW, but only for 30 fs at a time—and directed onto a thin metal foil accelerates electrons and protons perpendicularly to the foil's surface, say the researchers. But with a tilted laser pulse, the angle of the thin light disk is slightly tilted with respect to the axis of propagation, enabling the electrons to feel the rotation of the light disk and follow the direction in which the light hits the foil. What's more, protons are accelerated along this direction as well and, in contrast to the electrons, maintain their direction. This novel observation of the directional dependence allowed the researchers to also look directly at the underlying acceleration process.
What's next? The researchers now want to expand the DRACO laser to 500 TW, and are currently building a petawatt (equal to one quadrillion watts) laser system called PENELOPE. Also, the OncoRay center, which is jointly supported by HZDR, University Hospital, and TU Dresden, is building a modern proton therapy facility on the University Hospital's campus, which will be used for cancer research and therapy and will feature a high-performance laser prototype and conventional proton accelerator.
1. K. Zeil et al., Nat. Comm., 3, 874, doi:10.1038/ncomms1883 (June 6, 2012).