(color online) The evolution of THE bubble structure when the un-chirped laser pulse propagates through the under-dense plasma (n _e = 0.02n _c) at the times of: (a) t = 300 fs, (b) t = 500 fs, and (c) t = 600 fs. The laser pulse with the normalized amplitude of a ₀ = 10, the longitudinal size of σ _x = 10 µm, and the spot size of σ _y = 8 µm enters the simulation box from the left boundary.