Investigations of Vapor-Cell Clock Equilibration Following Initial Activation: A Progress Report

摘要

Over the past several years, anecdotal evidence has grown indicating that Rb gas-cell frequency standards exhibit a long equilibration period of somewhere between 30 and 70 days following their initial activation. The mechanism driving this behavior is not well understood and has been the subject of debate. Generally, lamp intensity has also been observed to undergo a slow variation following the clock s turn-on, and since the clock s resonant frequency depends on light intensity via the light-shift effect, there has been speculation regarding the light-shift as a possible mechanism for long-term equilibration. However, helium permeation has also been suggested as a contributing mechanism, since the gas cells are manufactured free of He and over time atmospheric He must permeate into the cells changing the clock frequency via the pressureshift effect. In order to characterize the nature and discern the mechanism of equilibration in Rb clocks, we have initiated a project to study the long-term (i.e., > 100 days) deterministic variations of Rb clocks from different manufacturers. Though our preliminary data confirms the anecdotal findings, the data at present are ambiguous regarding a causal relationship between long-term lamp-intensity change and clock-frequency change.