  Submicron-sized targets are found in intense laser-cluster interaction
experiments and laser-based material processing. Here we investigate the
internal field localization due to Mie scattering and its effect on ionization
dynamics in submicron-sized clusters using Mie calculation and particle-in-cell
simulations. As a result of intertwined processes of pulse propagation and
ionization, sub-micron nanofocusing dominates at lower intensity and gives rise
to an ionization hotspot at the rear of the targets while plasma shielding wins
over at a higher intensity, stopping further rear side ionization. As
ionization is often the precursor of other processes, understanding the
ionization dynamics of ultrafast laser pulses with wavelength-sized
nanostructure can be relevant for intense laser-cluster experiments and
femtosecond laser micro/nanomachining.
