@inproceedings{5f3e20c59f9a4abebc499bd72dd1b504,
title = "Astrophysical lasers in optical Fe II lines in gas condensations near η Carinae",
abstract = "We report here on the discovery of laser action in the range 0.9-2 μm in several spectral lines of Fe II, which are associated with transitions from {"}pseudo-metastable{"} states populated by spontaneous transitions from Lyα pumped Fe II levels. The intense Lyα radiation is formed in the HII region of gas condensations close to the star η Car. The laser transitions form together with spontaneous transitions closed radiative cycles, one of which includes the extremely bright 2507/09 {\AA} lines. This fact, together with an accidental mixing of energy levels, may provide an explanation of the abnormal intensities of these UV non-lasing lines. Using the complicated energy level diagram of Fe II we present those peculiar features, which are essential for the inverted population and laser effect: the pumping, the level mixing, and the {"}bottle neck{"} for spontaneous decay. The laser action is a new indicator of non-equilibrium and spatially non-homogeneous physical conditions as well as a high brightness temperature of Lyα in ejecta from eruptive stars. Such conditions are very difficult to probe by existing methods",
keywords = "spontaneous transitions, intense radiation, laser transitions, radiative cycles, abnormal intensities, UV nonlasing lines, energy level diagram, laser effect, optical pumping, level mixing, spontaneous decay, Fe<sub>+</sub>, 0.9 to 2 micron, stellar radiation, stimulated emission, astrophysical plasma, brightness temperature, eruptive stars, pseudometastable states, laser action, η Carinae, gas condensations, astrophysical lasers, optical Fe II lines",
author = "Sveneric Johansson and Vladilen Letokhov",
year = "2005",
doi = "10.1063/1.1928874",
language = "English",
volume = "770",
publisher = "American Institute of Physics (AIP)",
pages = "399--410",
booktitle = "Atomic Physics 19",
address = "United States",
note = "Atomic Physics 19. 19th International Conference on Atomic Physics ICAP 2004 ; Conference date: 25-07-2004 Through 30-07-2004",
}