Introduction to Special Issue on Frequency Control, Part I

I N 1982 the IEEE Group on Sonics and Ultrasonics (GSU) began cosponsoring the Frequency Control Symposium with the US Army, which had sponsored the meeting since its inception in 1947. Though the GSU has always had a connection with acoustic frequency control devices, this cosponsorship constituted an expansion of its technical activities into nonacoustic technologies such as atomic and molecular frequency standards and the theory of frequency and time characterization and dissemination. This expansion of technical interest was formally recognized when the group officially changed its name in January of 1986 to the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society (UFFC Society). To help stimulate and draw attention to the technical areas involved in frequency control it was decided that a special issue of the TRANSACTIONS ON ULTRASONICS, FERROELECTRICS A N D FREQUENCY CONTROL devoted to the subject of frequency control would be appropriate. Since the topic of frequency control encompasses a broad range of technologies, our team of five Guest Editors was formed to help organize this special issue. The response to the call for papers for the Special Issue on Frequency Control was so great that two issues of the UFFC TRANSACTIONS will be devoted to the topic. Part I (the 18 papers in this issue) is devoted primarily to atomic and molecular frequency standards (nine papers) and to frequency and time characterization and dissemination (four papers), though four bulk acoustic wave papers are also included. Part I1 (approximately 17 papers) will be published in May 1988 and will be devoted primarily to acoustic devices and materials. A tentative list of papers for Part TI is shown in Table I. We would like to thank all of the authors for their excellent papers, and we would especially like to welcome the authors of the nonacoustics papers to the UFFC Society. The traditional reference for long-term frequency stability and frequency accuracy has been and is based on the definition of the second as derived from the cesium133 atom. The typical standard is an atomic beam machine with magnetic energy state selection. As needs have arisen for better accuracy and improved frequency stabili ty, questions have been asked regarding how to gain these needed improvements. Some important answers are given in the papers of this issue’s first section, Atomic and Molecular Frequency Standards. In particular, new primary standards are hoped to gain significant improvements in accuracy and long-term frequency stability by using optical pumping for energy state selection and detection rather than magnetic selection. Also, different methods of locking to the center of the atomic resonance are being considered in order to deal with heretofore ignored biases and instabilities. The invited paper by Audoin et al. provides the theoretical basis for different kinds of modulation schemes and for the kinds of effects that will be encountered with optical pumping for energy state selection and detection, and hence is very relevant for future standards. The invited paper by DeMarchi extends the work of Audoin et al. into some of the very important areas dealing with biases and different modulation schemes surrounding the question of improved accuracy and long-term frequency stability. The invited paper by Walls provides a complementary treatment of why inaccuracies occur and how to avoid them by giving better understanding of the source of errors that have caused inaccuracies and instabilities in the past. The following paper by DeMarchi gives interesting experimental results as follow up from the theoretical developments from his previous work. Significant improvements in long-term frequency stability have already been obtained. The paper by Hurrell et al. discusses further results on cesium beam frequency standards, as does the paper by Jaduszliwer in the Correspondence section. The next paper by Comparo and Frueholz presents a comparison of various alkali gas cell frequency standards. Two papers are also presented on rubidium standards, with the invited paper by Riley and Vaccaro discussing a systems approach to oscillator design in which a crystal oscillator interrogates, as needed, a rubidium gas cell reference. The second rubidium paper, by Kuramochi et al . , discusses the performance of a gas cell using a mixture of 87Rb and 85Rb. The section Atomic and Molecular Frequency Standards concludes with the paper by Mattison et a l . , which focuses on substantial improvement in the performance of the atomic hydrogen maser through the use of a refined state selection system, which assures the presence of only one of the several states in the hydrogen storage