Narrowing spontaneous emission without intensity reduction

We show that it is possible at least in principle to have unbounded line na rrowing in the spontaneous emission spectrum simultaneously with control of the corresponding intensity. For this purpose we employ a laser driven dou blet of excited atomic, molecular, or semiconductor states with almost para llel dipole orientation, which is decaying to a ground state. Incoherent pu mping is applied to control the population and thus the spontaneous emissio n intensity of the dressed state associated with the ultranarrow spectral l ine.