Experimental demonstration of a compact and high-performance laser-pumped rubidium gas cell atomic frequency standard

The authors present a compact high-performance laser-pumped Rubidium atomic frequency standard exploiting the advantages of laser optical pumping for improved stability. The clock is based on an industrial Rb clock with the lamp assembly removed and optically pumped by light from a compact frequency-stabilized laser head. The modification of the buffer gas filling in the clock resonance cell reduces instabilities on medium-term timescales arising from the ac Stark effect and temperature variations. The frequency stability of the demonstrator clock was measured to be better than 4×10^-12τ^-12/ up to 10⁴ s, limited by the local oscillator (LO) quartz and RF loop electronics. Long-term drifts under atmosphere amount to 2-6×10^-13/day only, comparable to or lower than that for lamp-pumped clocks under similar conditions. Typical signal contrasts lie at around 20%, corresponding to a shot-noise limit for the short-term stability of 2×10^-13τ^-12/. The results clearly demonstrate the feasibility of a laser-pumped Rb clock reaching <1×10^-12τ^-12/ in a compact device (< 2 L, 2 kg, 20 W), given the optimization of the implemented techniques. Compact high-performance clocks of this kind are of high interest for space applications such as telecommunications, science missions, and future generations of satellite navigation systems [GPS, global orbiting navigation satellite system (GLONASS), European satellite navigation system (GALILEO)].