Fluorescence from doubly driven four-level atoms - A density matrix approach A. Narayanan, R. Srinivasan, U. K. Khan, A. Vudayagiri and H. Ramachandran Eur. Phys. J. D, 31 1 (2004) 107-112 Published online: 21 September 2004 DOI: 10.1140/epjd/e2004-00123-2