Curtis, E. A.Diddams, S. A.Oates, C. W.Udem, Th.Vogel, K. R.2004-12-142004-12-1420012001http://hdl.handle.net/2003/1890410.17877/DE290R-6682enThe American Physical SocietyPhysical Review Letters530Absolute Frequency Measurements of the Hg+ and Ca Optical Clock Transitions with a Femtosecond Laser10.1103/PhysRevLett.86.4996article (journal)