From optical to terahertz, frequency metrology with a single ion C. Champenois, G. Hagel, M. Houssin, M. Knoop, M. Vedel, C. Zumsteg and F. Vedel Ann. Phys. Fr., 32 2-3 (2007) 25-31 Published online: 23 May 2008 DOI: 10.1051/anphys:2008002