Frequency Standards and Metrology: Proceedings of the Fourth Symposium, Ancona, Italy, September 5 – 9, 1988

Since the previous Symposium, several exciting new developments and advances have occurred in the field of frequency standards and metrology. These include the first results on the long-tenn stability of a millisecond Pulsar, for which data 14 integrated over several years now show a stability of around 10- . Improvements in the understanding of various biases in Cesium beam standards promise accuracies in the low 14s for primary standards and in the low 13s for short commercial tubes, for which long tenn stabilities in low 14s have already been shown to be obtainable by accuracy improvement. Beams using optical pumping for state selection and for detection have been operated with excellent results, and more are being realized. Other new frequency standards which have appeared include a macroscopic rf trap with Mercury ions, which perfonns in the low 15s in one day, the sub millimeter metastable Magnesium beam, which has shown a short tenn stability 19 in the low 12s in one second and promises an accuracy of 10-, and the cold Hydrogen masers, which have such high stabilities that they cannot be measured with existing local oscillators. Prospects for future developments include laser manipulation of neutrals and spectroscopy of single ions at rest in a trap. Both these groups of techniques have great potential for unprecedented accuracy and short-and long-tenn stability, and new superior frequency standards are expected to be realizable in this way in the not too distant future."