Fundamental stability limits for the diode-laser-pumped rubidium atomic frequency standard

Recently, there has been considerable interest in the use of single-mode diode lasers in atomic frequency standards. In the present paper theoretical calculations are performed in order to quantify the expected performance improvement upon incorporation of diode lasers in rubidium gas cell atomic frequency standards. We assume that clock signal shot noise, the diode laser’s quantum noise, and diode laser frequency locking noise all contribute to the atomic frequency standard’s stability. Our results indicate that white-noise Allan variances of ∼6×10−15/(τ)1/2 are possible if enhanced cavity Q diode lasers are employed, whereas for presently available commercial diode lasers we predict white-noise Allan variances of ∼3×10−14/(τ)1/2. These variances represent a 2–3 orders of magnitude improvement in frequency stability over that currently obtained with rubidium gas cell atomic clocks.