Rayleigh-Taylor Instability of an Ultrathin Foil Accelerated by the Radiation Pressure of an Intense Laser

We report experimental evidence for a Rayleigh-Taylor-like instability driven by radiation pressure of an ultraintense (${10}^{21}\mathrm{W}/{\mathrm{cm}}^2$) laser pulse. The instability is witnessed by the highly modulated profile of the accelerated proton beam produced when the laser irradiates a 5 nm diamondlike carbon (90% C, 10% H) target. Clear anticorrelation between bubblelike modulations of the proton beam and transmitted laser profile further demonstrate the role of the radiation pressure in modulating the foil. Measurements of the modulation wavelength, and of the acceleration from Doppler-broadening of back-reflected light, agree quantitatively with particle-in-cell simulations performed for our experimental parameters and which confirm the existence of this instability.

Figure 1

Beam profiles for $\approx 4.4\mathrm{MeV}$ protons accelerated from (a) 5 nm, (b) 20 nm, (d) 30 nm, and (d) 50 nm DLC targets. The films are placed as they would appear looking from the interaction toward the stacks. The cutout holes allow lines of sight for other diagnostics. The red star shows the position of the laser axis while the dashed red line highlights the “ring.” (e) includes consecutive films from the 5 nm target, presenting the profile at several proton energies.

Figure 2

(b) Burn pattern, created by the transmitted laser imprinting on the aluminum foil protecting the front surface of the radiation detector stack from laser damage, compared side-by-side with (a) corresponding proton profile. Examples of (anti)correlation of features within the two images are highlighted by the green ellipses.

Figure 3

Carbon spectra, from the on-axis (0°) TP, for various foil thicknesses, showing that decreasing target thickness leads to slow increase in maximum energy with a prominent peak for the $d=5\mathrm{nm}$ target.

Figure 4

Simulation snapshots of (a) laser intensity, $⟨a^2⟩$; (b) carbon ion density; and (c) proton density for a simulation with $d=10\mathrm{nm}$ (312 fs after the pulse first reaches the target).