  Direct laser acceleration of ions by short frequency-chirped laser pulses is
investigated theoretically. We demonstrate that intense beams of ions with a
kinetic energy broadening of about 1 % can be generated. The chirping of the
laser pulse allows the particles to gain kinetic energies of hundreds of MeVs,
which is required for hadron cancer therapy, from pulses of energies of the
order of 100 J. It is shown that few-cycle chirped pulses can accelerate ions
more efficiently than long ones, i.e. higher ion kinetic energies are reached
with the same amount of total electromagnetic pulse energy.
