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Optical clocks and frequency standards are now challenging the best microwave fountain clocks. This paper reviews the current state of the art in optical clocks. The comparative performance of various clock species is described, and consideration is made of the implications for a future redefinition of the second
The 1S0-3P0 transition in neutral strontium is being considered as one of the choices for the future redefinition of the SI second. At the National Physical Laboratory we are designing and implementing an optical clock based on this transition, holding the atoms in an optical lattice during the clock interrogation cycle, which greatly increases the potential accuracy of the clock. Our focus is on...
In this paper, a pair of diode lasers at 674 nm, locked to two independent ultralow-expansion high-finesse cavities, have been characterized by monitoring the beat frequency between them. The individual laser linewidth of 1.4 Hz for a 3-s averaging time broadened to 4 Hz at 30 s. The relative frequency stability of the beat at 1s is 2.5 10-15. One of the lasers has been used to interrogate the 88Sr...
Forbidden transitions in single laser-cooled trapped ions provide highly stable and accurate references for optical frequency standards. This paper describes recent progress on strontium and ytterbium ion optical frequency standards under development at NPL.
The emergence of microwave and optical frequency standards with accuracies close to those of caesium primary frequency standards has led to the concept of secondary representations of the second. The recently-formed Joint Working Group of the CCL / CCTF has now recommended as secondary representations to the CCTF / CIPM one microwave radiation in 87Rb and three optical radiations in 199Hg+, 88Sr+...
Controlled modulation of laser phase in an optical Ramsey experiment yields an antisymmetric lineshape. This discriminant is used to stabilize a local oscillator to the optical clock transition in a single 88Sr+ ion
Summary form only given. A single laser-cooled ion held in an electrodynamic trap is a near ideal atomic sample for a frequency standard. The quantum jump technique is used to observe a high-Q forbidden transition in the ion. It has been suggested that the ultimate limit to the reproducibility of a standard of this type will lie in the region of one part in 10/sup 18/.
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