Light Sail Acceleration of Ions

The applicative potential of high energy ion beams involving proton probing, production of warm dense matter, fast ignition of fusion targets, nuclear physics and biomedical applications, and the thrust on investigating the novel regimes of ion acceleration is the motive to  focus on non-linear interaction of an ultra-short, ultra-intense (intensity of the order of 10²²-10²⁴ W cm^-2) laser pulse with an ultra-thin solid target in radiation pressure dominant  regime(RPD). The ~ tera bar pressure of such super-intense laser pulses causes the direct acceleration of ions making it the most efficient mechanism. The relativistic non-linear laser-plasma foil interaction depends on many parameters; laser intensity pulse profile, pulse group velocity, target density etc.  The analytical and numerical results exhibit the ion momentum/energy, their numbers, and dependence upon the pulse profile.  For optimum energy transfer from the pulse to the ion during the interaction, the foil should be opaque requiring proper matching of the target to the laser pulse.  Also, a Lorentzian laser pulse incident on a thin hydrogen foil can generate ~ 10¹⁰ protons, almost monoenergetic in the energy range ~ 230 MeV,  resulting in a proton beam  that makes  it a suitable candidate for hadron therapy applications. The momentum/energy that a laser pulse transfers to the ions depends on the  pulse profile as well as the group velocity of the incident  laser pulse. In the RPD regime, excluding the group velocity effec the energy imparted to the plasma ions by the Lorentzian pulse came out to be ~ 2.67 times greater than those transferred by the Gaussian pulse. On the other hand taking into account the group velocity, this value becomes ~ 2.46 times. Interaction of an intense laser pulse with flat target leads to an expansion of the plasma foil in the transverse direction resulting in decrease in the accelerated ions in longitudinal direction and hence energy per ion is increased. The surface density of the expanded plasma foil also affects the transparency of the thin foil; and with laser group velocity effect, the transverse expansion of the plasma foil is reduced due to early termination of the ion acceleration process. The group velocity effect is dominant over the transverse expansion effect.