Stimulated amplification under spatially nonhomogeneous conditions: An astrophysical FeII laser in the vicinity of eta carinae

Abstract:
We consider the conditions necessary for the development of an inverted population among the energy levels of free atoms in a medium exposed to radiation in spectral non- equilibrium. In particular, we focus on monochromatic radiation occurring as a result of an accidental wavelength coincidence between a pumping emission line and a pumped absorption line in two different elements. We examine especially the influence of "pseudo-metastable" states ( at medium excitation) in the complex spectrum of Fe II, which cause a "bottleneck" in the radiative decay leading to an inverted level population. We also discuss the effect of "spectral compression" of the Lyman continuum into HLy alpha radiation at a high effective temperature. In conclusion we describe those differences between microwave astrophysical masers (APM) and optical astrophysical lasers (APL) that make the latter a more rare phenomenon in Nature.