Observation of radiation pressure driven Rayleigh-Taylor instability

Radiation pressure acceleration (RPA)$\left[1\right]$ uses the high pressures of a high intensity laser pulses to accelerate low mass targets to high energy with potentially low energy spreads. However, simulations have shown susceptibility to the radiation pressure driven Rayleigh-Taylor instability $\left[1,2\right]$. Here we report on experiments performed with the VULCAN Petawatt laser at the Rutherford-Appleton Laboratory using intensities up to $10^{21}$~Wcm$^{-2}$ in linear polarisation. Peaks within the C$^{6+}$ spectra indicate RPA acceleration of the foils. Most remarkably though, strong spatial modulation is observed in the recorded proton beams. The form and extent of these modulations suggest Rayleigh-Taylor break-up of the foil. Simulations provide further support for these conclusions.\\ $\left[ 1 \right]$ A.P.L. Robinson et al., NJP, \textbf{10}, 013021 (2008)\\ $\left[ 2 \right]$ F. Pegoraro et al., PRL, \textbf{99}, 065002 (2007)