A compact, high-performance laser-pumped rubidium frequency standard

We present the realisation of a compact and high-performance Rubidium atomic frequency standard under development for space applications. The clock comprises a compact frequency-stabilised diode laser head for optical pumping of a lamp-removed industrial Rb clock module, in order to exploit the advantages of laser optical pumping for optimised short- term stability. We obtain typical signal contrasts around 20%, resulting in an estimated signal-to-noise limit for the short- term stability of about 1middot10^-12 tau^-1/2. Modification of the buffer- gas filling in the clock resonance cell allows to reduce instabilities arising from the AC Stark effect and temperature variations, that limit the clock stability on longer timescales. The clock stability of the realised demonstrator breadboard was measured to be better than 4middot10^-12 tau^-1/2 up to 10⁴ seconds, already meeting the specifications for the GALILEO Rb clocks. Further optimisation should allow the realisation of a laser-pumped Rb clock reaching 3middot10^-13 tau^-1/2 in a compact device (<1.51, 1.5 kg, 15 W). Such compact and high- performance clocks can find their applications in telecommunications, science missions, and future generations of satellite navigation systems (GALILEO, GPS).