Spontaneous emission spectra S(δ_k) (in units of ) each as a function of detuning frequency δ_k for different relative phases of the coupling fields. (a) θ = 0, (b) θ = π/6; (c) θ = π/4, (d) θ = π/2. The other parameters are set to be |Ω₁| = 1, Ω₂ = 1, Ω₃ = 1, A₁(0) = 1, A₂(0) = 0, A₃(0) = 0, δ_14c1 = −0.36, and δ_14c2 = 0.36.