Atomic Clocks and Frequency Stabilization on Microwave Spectral Lines

Abstract

Application of the various types of radiofrequency spectral lines to accurate frequency stabilization and time standards is surveyed. Pertinent characteristics of microwave gas absorption lines and the various types of errors in frequency stabilization due to the nature of these absorption lines or to fundamental thermal noise are discussed in detail. It is shown that time standards synchronized with microwave absorption in ammonia or resonances in molecular or atomic beams have limits of accuracy of the order of 1 part in 10¹² for a short time, and still smaller limiting fractional errors over longer periods of time.