Atomic frequency standards: new trends and progress at nrc

The paper reviews the state of the art of primary laboratory atomic frequency standards. Emphasis will be put on the new techniques being used in the field such as ion trapping, laser cooling and optical pumping, to implement more accurate primary optical or microwave frequency standards. Progress made at NRC on the subject will be outlined. Finally the central role of time as a base quantity of the international system of units will be discussed.