Dark-line in optically-thick vapors: inversion phenomena and line width narrowing A. Godone, F. Levi, S. Micalizio and J. Vanier Eur. Phys. J. D, 18 1 (2002) 5-13 Published online: 15 January 2002 DOI: 10.1140/e10053-002-0001-z