We present the experimental realisation of a laser optically-pumped vapour-cell atomic frequency standard ("Rb clock") using a DFB laser diode as pump light source. This development aims to fully exploit the advantages of narrowband laser pumping over discharge lamps commonly used as pump light sources in Rb clocks. These advantages include, e.g., improved control over the pump light spectrum and increased signal contrast, and thus show potential for the realisation of Rb atomic clocks with improved frequency stability [1]. Such compact (< 1.5 Litres) Rb clocks with high medium-term frequency stability (10{sup}(-14) between 10'000 s and one day) could find their applications for example in satellite navigation systems or in telecommunication applications. For such space applications, it is essential to implement laser diodes such as DFB or DBR lasers, showing reliable single-mode operation directly from the laser chip without need for external optical feedback, which helps to reduce the sensitivity of the overall clock to environmental disturbances such as, e.g., vibrations. Our Rb clock is based on probing the ground-state hyperfine "clock" transition (m{sub}F=0→0) at 6.8 GHz of atomic 87Rb, by optical-microwave double-resonance technique. The Rb atoms are confined in a small glass cell also containing a buffer gas for narrowing of the clock transitions linewidth. The optical pump radiation acts on the D2 transition, and the microwave field probing the clock transition is applied via a small magnetron-type microwave cavity (we use a modified, lamp-removed industrial space Rb clock module, RAFS type, Temex Neuchatel Time). The pump light is provided by a DFB laser diode emitting at 780nm (from Ferdinand-Braun-Institut fur Hochstfrequenztechnik, Berlin [2]), integrated into a compact (200cm{sup}3 physics package volume) laser module for laser frequency stabilisation. The laser shows FM noise levels around 5 kHz Hz{sup}(-1/2) and AM RIN ≈ 5×10{sup}(-14)/Hz, and an emission linewidth around 7 MHz, sufficiently narrow to allow stabilisation of the laser frequency to sub-Doppler saturated absorption resonances by acting on the laser current.
展开▼
