Abstract
Strong environmental dependence is an intractable problem for vapor cell clocks, for which the high-temperature sensitivity of the physics package is considered one of the dominant reasons. In this paper, we report the design and realization of a low-temperature-sensitive physics package for vapor cell clocks. The physics package comprises three layers of magnetic shields, three layers of heating ovens, and the cavity-cell assembly. The cavity-cell assembly employs a compact magnetron-type cavity and a Rb vapor cell sealed with N2-Ar mixed buffer gas. The dependence of the clock frequency on temperature fluctuation is evaluated to be 2 × 10−11/°C. In pursuit of the stable temperature, a three-stage temperature regulator is implemented on the physics package. It adopts a combination of open andclosed-loop control to address the problem of significant thermal coupling between the heating ovens. Under a laboratory environment, the measured Hadamard deviation of the temperature variation is 4 × 10−5 °C in 1 day of averaging.
Highlights
In recent years, vapor cell atomic clocks, which play an important role in Global Navigation Satellite Systems (GNSSs), have attracted considerable attention (Camparo 2007; Godone et al 2015)
It is noteworthy that the shot noise limitations of the pulsed optically pumped (POP) Rb clock and the coherent population trapping (CPT) Cs clock are far beyond their measured performances
As the temperature sensitivity of the physics package has been identified as a major limitation for long-term stability (Micalizio et al 2012; Calosso et al 2012), the primary aim of this study is to realize a low-temperature-sensitive physics package for high-performance vapor cell clocks, which could benefit the ground-based applications, including GNSS user terminal, very long baseline interferometry (VLBI), and telecommunication
Summary
Vapor cell atomic clocks, which play an important role in Global Navigation Satellite Systems (GNSSs), have attracted considerable attention (Camparo 2007; Godone et al 2015). Vapor cell clocks in different configurations, including lamp-pumped Rb clock (Hao et al 2016), continuous-wave laser-pumped Rb clock (Bandi et al 2014), pulsed optically pumped (POP) Rb clock (Micalizio et al 2012), and coherent population trapping (CPT) Cs clock (Abdel Hafiz et al 2018), have shown excellent short-term (less than 100 s averaging time) stabilities better than 3 × 10−13 τ−1/2. To obtain a better long-term (10,000 s or even longer) frequency stability, the vapor cell clocks are generally placed in the vacuum chamber or the thermostat for ground-based applications. This strategy increases the cost and size of vapor cell clocks
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