Fig. 1. Energy level structure of atomic system and position relation between fields and atomic system. (a) Four-level N-type atomic system; (b) spatial configuration of probe, modulation, and coupling fields with respect to atomic sample in which zeroth-order, first-order and second-order diffraction directions are indicated

Fig. 2. Transmission function and corresponding diffraction intensity of probe field when Δ_c=0, Δ_m=0.68γ, Δ_p=-0.05γ, Ω_c=0.27γ, Ω_m=0.35γ, and L=140z₀ . (a) Amplitude and phase of transmission function of probe field versus x; (b) diffraction intensity versus sin θ under different phase modulation conditions; (c) part with zeroth-order diffraction int

Fig. 3. Im (χ) versus Rabi frequencies of modulation field and coupling field when Δ_c=0, Δ_m=0.68γ, Δ_p=-0.05γ, and L=140z₀. (a) Im (χ) versus Rabi frequency of modulation field; (b) Im (χ) versus Rabi frequency of coupling field

Fig. 4. High-order diffraction intensity versus Ω_c and Ω_m when Δ_c=0, Δ_m=0.68γ, Δ_p=-0.05γ, and L=140z₀.(a) First-order diffraction intensity; (b) second-order diffraction intensity; (c) third-order diffraction intensity

Fig. 5. High-order diffraction intensity versus Δ_p and Δ_m when Δ_c=0, Ω_c=0.27γ, Ω_m=0.33γ, and L=140z₀. (a) First-order diffraction intensity; (b) second-order diffraction intensity; (c) third-order diffraction intensity

Fig. 6. First-order diffraction intensity versus Ω_m for different L when sin θ₁=0.25, Δ_c=0, Δ_m=0.68γ, Δ_p=-0.05γ, Ω_c=0.27γ, and L=140z₀