Ultracold calcium atoms for an optical frequency standard and cold collision studies

High resolution spectroscopy is performed on ultracold calcium atoms to examine their potential for improving the optical calcium frequency standard in accuracy and stability. The ultracold atoms have been used in asymmetric frequency dependent four pulse Ramsey-Borde interferometers. In contrast to the Doppler cooled atoms the Fourier width of the exciting laser pulses is broader than the Doppler width of the atomic ensemble. This allows almost all atoms to take part in the interferometry. A shelving detection method was applied to the ultracold atoms. To gain a better understanding of cold collisions that lead to frequency shifts in the optical frequency standard, photoassociation spectroscopy (PAS) measurements are performed.