Narrowing Spontaneous Emission without Intensity Reduction

We show that it is possible at least in principle to have unbounded line narrowing in the spontaneous emission spectrum simultaneously with control of the corresponding intensity. For this purpose we employ a laser driven doublet of excited atomic, molecular, or semiconductor states with almost parallel dipole orientation, which is decaying to a ground state. Incoherent pumping is applied to control the population and thus the spontaneous emission intensity of the dressed state associated with the ultranarrow spectral line.