Phase-sensitive microwave optical double resonance in an N system T. M. Preethi, M. Manukumara, K. Asha, J. Vijay, D. A. Roshi and A. Narayanan EPL, 95 3 (2011) 34005 Published online: 15 July 2011 DOI: 10.1209/0295-5075/95/34005