(Color online) Beam width parameters f₊ and g₊ plotted against the dimensionless distance of propagation ζ for different values of intensity parameter a at ω_c/ω_o = 0.5, ω_p/ω_o = 0.1, x_o/r_o = 0.6, r_o = 10 μm and τ_o = 20 fs. (a) Variation of f₊ in the absence of self-compression effect; (b) Variation of g₊.