Image showing the laser (in red) irradiating a thin target and accelerating ions in the laser forward direction. Credit: Isabella Cortrie, Ludwig Maximilian University of Munich
The enormous force from radiation pressure exerted onto a nanometer thin diamond–like carbon (DLC) foil by a high intensity laser pulse can enhance efficient acceleration of carbon ions. Kinetic energies up to 30 MeV were reached in an initial experimental demonstration of this novel radiation pressure acceleration scheme (RPA) in 2009. Those studies revealed grand technological challenges posed by current laser technology in the pursuit of peak intensities well beyond 1021 W/cm² with ideally abrupt temporal profiles.
However, experimental results obtained using the Gemini laser reveal that the intensity-dependent relativistic mass-increase of the electrons when the laser is interacting with dense plasmas, can form strong nonlinearities that tightly focus the laser to a near-diffraction limited spot size and temporally steepen the pulse front. This novel relativistic plasma-optic effect was realised by employing a sophisticated target design - depositing micrometer thin carbon-nanotube foam onto DLC target foils.
These multi-layer targets were tested in a collaborative Laserlab-Europe experiment that brought together researchers from Germany, the UK, Spain and China. Radiation Pressure Acceleration of carbon ions up to 240 MeV kinetic energy was demonstrated using this technique.
This recent accomplishment is an important milestone for research focused on laser-driven ion acceleration at the Munich centre for Advanced Photonics (MAP Centre of Excellence Cluster) and shows promise for extending kinetic energies to the GeV level for envisioned applications at the Centre for Advanced Laser Applications (CALA) in Munich.
The work was published in Physical Review Letters: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.064801 (link opens in a new window)
