An optically pumped cesium beam resonator has been designed including three successive magnetic field regions. The optical interactions take place in the first and third regions, where the magnetic field has the required value of 3x10(-5) T. The microwave interaction occurs in the intermediate region, where the value of the C-field is typically set to 4x10(-6) T. It has been verified that the magnetic field profile along the cesium beam does not induce Majorana transitions. Using a single laser diode emitting at 852 nm with a linewidth of about 30 MHz, the resonator gives an excellent amplitude signal to noise ratio equal to 20000 in a 1-Hz bandwidth.

We have measured a figure of merit for a caesiumbeam frequency standard in which optical pumping and optical detection are accomplished by a single semiconductor laser source. The value of this figure of merit is 29, leading to an estimated fractional frequency stability of 2.6 × 10-12 τ-1/2. This result compares very favorably with the frequency stability of the best manufactured caesium-beam frequency standards.