  Usage of double-layer targets consisting of heavy and light material with
modulated interface between them provides a way for laser-driven generation of
collimated ion beams. With extensive 2D3V PIC simulations we show that this
configuration may result in a development of a relativistic instability with
Rayleigh-Taylor and Richtmyer-Meshkov like features. Initially small
perturbations are amplified during the laser-target interaction leading to the
formation of low-density plasma regions and high-density bunches between them,
which are accelerated by the laser radiation pressure as whole compact
structures. That results in collimated quasi-monoenergetic proton beam with
high average energy. The properties of this proton beam such as its low
emittance (one order of magnitude lower compared to that of conventional
accelerators) and divergence are discussed. Results are compared with similar
acceleration schemes such as double-layer target without corrugation and
single-layer target.
