Petawatt laser ion acceleration with nanometer scale diamond-like carbon targets

Introduction Ion acceleration with high intensity laser pulses is a fast advancing area of research. There is a wide range of applications for controllable energetic ion beams including proton probing , isotope production [2] and hadron therapy [3] – a novel cancer therapy. Advancements in laser physics, specifically the development of chirped pulse amplification , have allowed the investigation of new acceleration regimes . One such regime is that of target normal sheath acceleration (TNSA) in which hot electrons, accelerated by the laser, pass through the target and escape from the rear surface forming a strong electric field (~1012 V/m) at the target surface that is sufficient to ionise the rear surface atoms and accelerate the resulting ions . The ion energy scaling with laser intensity for this TNSA mechanism is proportional to (Iλ2)1/2 implying that at higher intensities higher energies will be achieved, however, theorists have predicted that as the laser intensity is increased beyond 1023 W/cm2 a new accelerating regime can be accessed. This regime is termed radiation pressure acceleration (RPA) and exhibits much more favourable ion energy scaling with increasing intensity than TNSA (proportional to (Iτ/σ)α, where I is the intensity, τ is the pulse length, σ is the areal density and α is a constant equal to 2 for non-relativistic ion energies) .