Figure 2.

(a–c) Results of WAKE simulations. (a) Schematic showing longitudinal position of the hypergaussian gas plasma density profile relative to the simulation box. (b) Ratio of vacuum peak intensity I₀ and peak intensity inside plasma I_M as a function of position z (z_R = Rayleigh length). (c) Ratio of laser beam size at the entrance r₀ and inside plasma r. (d–g) Experimental measurements, showing variation in observed ion energy distributions of the two ionic species He⁺ and He⁺⁺ as density is tuned from extremely underdense to mildly underdense regime. n_c is critical density given by , where ω_L, m_e and e are laser frequency, electron mass and electron charge respectively.