Modulation-dependent FWM lines for relative larger inner-dressing strength: (a) and (b) for different dressing strengths g 2 / γ 10 = g 2 ′ / γ 10 = 0.6 (square), 1 (solid circle), 1.5 (upward triangle), 2 (downward triangle), and 3 (rhombus), respectively; the probe detunings for panels (a) and (b) are Δ 1 / Δ = 0.5 and 0.48, respectively; (c) for different modulation frequencies ν / Δ = 0.46 (square), 0.48 (solid circle), 0.5 (upward triangle), 0.52 (downward triangle), and 0.54 (rhombus), respectively; and (d) for different modulation amplitudes A = 1 (square), 1.8 (solid circle), and 3 (upward triangle), respectively. Other parameters are taken as A = 1 in panels (a), (b) and (c), g 2 / γ 10 = g 2 ′ / γ 10 = 3 in panel (c), and ν / Δ = 0.5 in panel (d), respectively.