E.J. Salumbides, V. Maslinskas, I.M. Dildar, A.L. Wolf, E.-J. Van Duijn, K.S.E. Eikema, W. Ubachs
We have performed an accurate frequency calibration of the 4s2 1S 0→4s4p 1P1 principal resonance line of the neutral calcium atom at 423 nm. Doppler-free cw excitation on a Ca atomic beam was performed by utilizing a Sagnac geometry in the alignment of the excitation beams. From frequency calibrations against a frequency comb, stabilized to a global positioning system (GPS) disciplined Rb standard, the transition frequency is determined at 709 078 373.01(35) MHz for the main Ca40 isotope. Slightly lower accuracies are obtained for the transition frequencies of the less abundant isotopes. The achieved fractional uncertainty of 5×10 -10 exceeds the requirements for including this transition in investigations that aim to probe a possible variation in the fine-structure constant α on cosmological time scales. © 2011 The American Physical Society.
Institute for Lasers, Life and Biophotonics Amsterdam, VU University, 1081 HV Amsterdam, De Boelelaan 1081, Netherlands; Kamerlingh Onnes Laboratory, Leiden Institute of Physics, NL-2300 RA Leiden, P.O. Box 9504, Netherlands; Department of Physics, University of San Carlos, Cebu 6000, Philippines
