Extended Data Fig. 12: The nonlinear (THz-field-dependent) refractive index of the graphene film.
From: Extremely efficient terahertz high-harmonic generation in graphene by hot Dirac fermions
a, The THz refractive index of the graphene film as a function of frequency at various peak electric fields for the THz pump at 0.3 THz, showing reduction in the refractive index with both frequency and exciting field strength. b, The field dependence of the nonlinear THz refractive index at the harmonics 3f = 2.04 THz generated by 1f = 0.68 THz pump, 5f = 1.85 THz generated by 1f = 0.37 THz pump, and 7f = 2.1 THz generated by 1f = 0.3 THz pump.
