Abstract

When an intense Gaussian laser pulse (I > 10²¹ w/cm²) with Circular Polarization (CP) is incident on a planar thin foil, the foil is curved and is transformed into a “cocoon”. Rayleigh-Taylor (R-T) like instabilities[1] develop much more slowly as the radiation pressure is increased, so that these instabilities can disperse nearly the whole cocoon into low density plasma cloud and only a clump (with a size about 1~2λ) is left in the center of the target[2,3]. As long as the laser gradually penetrates into the plasma cloud, the photon cavity can be formed and the laser pulse begins to embrace the clump. As the central clump is focused and pushed by the photon cavity (the three-dimensional beam compression), a mono-energetic and highly collimated proton beam is realized. The energy spread is close to the maximum value estimated by the 1D model of PSA given in Ref.[4]: $\frac{\Delta w}{w_r}\cong \frac{2\Delta p}{p_r}\cong \frac{2{\xi }_0\Omega }{p_r}$, where w_r, p_r and ξ₀ are the kinetic energy, normalized momentum of the reference particle and the oscillating amplitude, respectively.

© 2009 IEEE