This paper studies the interaction of a Λ-type three-level atom with a single mode field.It discusses the emission spectrum characteristics of the Λ-type three-level atom driven by the photon-added coherent field.By means of the second-order degree of coherence,it shows some nonclassical properties of the cavity field,such as sub-Poissonian photonnumber distribution and the two-time intensity-intensity correlation which violates the Cauchy-Schwarz inequality.
