Surface plasma waves excitation

Ultra-short (fs) intense (relativistic) laser interaction with modulated over-dense plasmas (produced from a thin grating target having a periodic groove on its front surface) was numerically and experimentally investigated.

In over-dense plasmas, laser energy is usually weakly absorbed within an optical skin depth but, when surface plasma waves (SPWs) can be excited, as it was shown to be the case for pre-structured plasmas, this coupling is significantly increased (up to 80%). Particle acceleration, and consequently radiation production, can then be improved. The topic was explored by A. Bigongiari during her PhD work, supervised jointly by M. Raynaud (LSI) and C. Riconda (TIPS). Thanks to PIC simulations (figure right showing the laser electric field impinging onto a modulated target as a function of space; the target surface is visible at x~250), it was evidenced that the maximum ion energy obtained at the rear of a modulated target is roughly twice the energy at the rear of a flat target. Such a result motivated an experimental campaign on the UHI100 laser facility. Ultra-high contrast allowed demonstrating – for the first time - an enhanced laser-target coupling in the relativistic regime (at ultra-high intensity, above 10¹⁹ W/cm²) due to SPW excitation.

An increase by a factor of 2.5 of the cut-off energy of the protons produced by Target Normal Sheath Acceleration from modulated targets (compared to plane targets) was indeed observed at an incidence angle close to the expected value for resonant excitation of surface waves.

Relevant publications

- A. Bigongiari et al., Phys. Rev. E 84, 015402 (2011)
- A. Bigongiari et al., Phys. Plasmas 18, 102701 (2011)
- A. Bigongiari et al., Phys. Plasmas 20, 052701 (2013)