Defocusing role in femtosecond filamentation: Higher-order Kerr effect or plasma effect?*
Li Su-Yua),b), Guo Fu-Minga),b), Yang Yu-Juna),b), Jin Ming-Xinga),b)
       
Change of the nonlinear refractive index Δn with the laser intensity. (a) The solid black curve denotes the contribution of the second-order Kerr effect to nonlinear refractive index, and the dashed red and dotted blue curves present the change of Δn = n 2 I − ρ e/ ρ c with the intensity I as the MPI cross section is σ 8 = 2.88 × 10−99 s−1 · cm16 · W−8 and σ 8 = 2.81 × 10−96 s−1 · cm16 · W−8 respectively; (b) the solid black curve denotes the contribution of Kerr effects to nonlinear refractive index, and the dashed red and dotted blue curves present the change of Δn = n 2 I + n 4 I 2 + n 6 I 3 + n 8 I 4 − ρ e/ ρ c with the intensity I as the MPI cross section is σ 8 = 2.88 × 10−99 s−1 · cm16 · W−8 and σ 8 = 2.81 × 10−96 s−1 · cm16 · W−8 respectively.