Abstract

Among the ions proposed for a frequency standard in the optical domain, Ca⁺ is one of the most favorable candidates due to its wavelengths accessible with all-solid-state laser systems. This allows to imagine an ultimate experimental setup being simple and compact. The 4S_1/2-3D_5/2 electric quadrupole transition at 729 nm with a natural linewidth below 1 Hz serves as clock transition, while laser cooling on one of the resonance lines is carried out at 397 nm. To obtain the small spectral linewidths necessary for a frequency standard performance, it is essential to reduce the residual Doppler broadening caused by the rf heating in the Paul trap. The 1^st order Doppler broadening of a single ion can be eliminated in the Lamb-Dicke regime where the ion’s amplitude of motion is inferior to the emitted wavelength. The main condition for the access of this frequency modulation regime is a high motional frequency of the trapped ion. This is more easily obtained in a low capacitance device and thus traps with reduced dimensions are required.

© 2000 IEEE