Fig. 3
From: Enhancing laser beam performance by interfering intense laser beamlets
Definition of the modulation angle α and its relation to the conversion efficiency. a Plasma electron density profile with 1.5 nc ≤ ne ≤ 6 nc for single beamlet and 2-beamlet interaction for all values of P investigated. The single beamlet case shows a rather uniform density profile while the 2-beamlets cases shows a significant surface modulation with period corresponding to the interference intensity pattern. For larger periods (2.9 μm ≤ P ≤ 11 μm) the depth of the surface modulation is approximately constant, leading to larger values of α as P decreases. However, for P < 2.9 μm the modulation depth also decreases since the wavelets full width at half maximum approaches the electron excursion length in the laser field. This leads to the saturation of α reaching its maximum for P = 2.9 μm and subsequently decreasing for smaller values of P. b Representation of a single wavelet-induced modulation for P = 11 μm. The average modulation angle α is defined as the average wavelet incidence angle on the plasma critical surface. c Laser-to-electron energy conversion efficiency as function of the average surface modulation angle α. The conversion efficiency linearly increases for all values of α. The dashed line-delimited area above 40 degrees represents the region where saturation and decline of conversion efficiency for forward moving electrons is expected
