Analytical study of four-wave mixing with large atomic coherence E. A. Korsunsky, T. Halfmann, J. P. Marangos and K. Bergmann Eur. Phys. J. D, 23 1 (2003) 167-180 Published online: 04 February 2003 DOI: 10.1140/epjd/e2003-00029-5