The interaction between a single two-level atom and the combination of a frequency converter and the sub-harmonic generationM. Sebawe Abdalla, M. M. A. Ahmed, A. S. -F. Obada and E. M. KhalilEur. Phys. J. Plus, 129 9 (2014) 193DOI: https://doi.org/10.1140/epjp/i2014-14193-0