Towards a miniature laser-pumped cesium cell frequency standard

With the goal of minimizing the overall size of a gas cell frequency standard the authors have characterized cylindrical Cs cells with inner dimensions R=2 mm and L=18 mm. Under conditions of present interest the lifetime in the absence of a tuned microwave field tends to be dominated by Cs-Cs collisions. Wall collisions have only a marginal effect on the lifetime, provided appropriate conditions on the N₂/Ar buffer gas pressure, are satisfied. Using a Te₁₀₁ mode rectangular cavity the microwave resonance lineshape signal parameters were measured over a range of optical and microwave powers at various cell temperatures and used to predict the achievable short term stability. For the optimum combination of optical and microwave powers the linewidth is dominated by power broadening, and the short term stability, σ(τ), predicted from these measurements decreases from σ(τ)τ^1/2=6.4×10^-12 to 4.2×10^-12, where τ is in seconds, as the cell cold spot temperature is raised from 50°C to 65°C