Ultranarrow extraresonant holes and antiholes in pump–probe and four-wave mixing spectroscopy of a two-level system interacting with two fields of arbitrary intensity

We study pump–probe and four-wave mixing spectroscopy for moderately intense copropagating pump and probe beams (Rabi frequencies 2V_{1, 2}) interacting with an open two-level system where the lower state of an optical transition relaxes faster to reservoir states than the upper state does. The probe absorption spectrum displays an ultranarrow extraresonant antihole (ERA) when V₁ ≥ V₂ and a ultranarrow dip when V₁ < V₂. The pump and probe absorption profiles display opposite tendencies except for the case of V₁ = V₂ when identical ERA’s are produced. The four-wave mixing spectrum shows an extraresonant dip for V₁ ≥ V₂ and an ERA when V₁ < V₂ The subnatural features are not power broadened.