  Collisionless shock acceleration of protons and C$^{6+}$ ions has been
achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $\mu$m laser with a
near-critical density plasma. Ablation of the initially solid density target by
a secondary laser allowed for systematic control of the plasma profile. This
enabled the production of beams with peaked spectra with energies of 10-18
MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within
these narrow spectral features. The narrow energy spread and similar velocity
of ion species with different charge-to-mass ratio are consistent with
acceleration by the moving potential of a shock wave. Particle-in-cell
simulations show shock accelerated beams of protons and C$^{6+}$ ions with
energy distributions consistent with the experiments. Simulations further
indicate the plasma profile determines the trade-off between the beam charge
and energy and that with additional target optimization narrow energy spread
beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.

Plasma Physics;Accelerator Physics