Industrial development of an optically pumped Cs beam frequency standard for high performance applications

Since 2003, Thales Electron Devices (Thales ED) develops frequency standards activities with the objective to set-up an industrial and reliable European source of Cs beam tubes and Cs clocks for space, metrology, military and telecom applications. In the framework of these activities Thales ED realizes an industrial prototype based on the technology developed by Tekelec and transferred to Thales ED end of 2003. Thales ED's objective is to demonstrate the frequency performances required for ground applications with technical solutions compatible of the industrial means. The main critical item in a industrial Cs frequency standard is the atomic resonator. Several compact laboratory breadboards demonstrated frequency unstability down to 1.4×10^-12 τ^-1/2 with the two laser frequencies optical configuration, and 4×10-12 τ^-1/2 with the single laser frequency setup. [1] The atomic resonator developed by Thales ED gives a quality factor in magnitude of 14×10⁶ and a measured signal to noise ratio in a 1Hz bandwidth higher than 12000 leading to a theoretical stability lower than 4×10^-12 τ^-1/2. This demonstrator, realized with industrial processes, includes a 2 liter vacuum chamber and uses the single frequency laser optical configuration. Contrary to other industrial developments [2][3], we chose this simplest optical architecture in view of space developments. An optimization study allowed us to identify significant potential improvements on sub-systems of the Cs tube. This lead us to be confident in the achievement of the frequency stability required for satellites navigation systems such as Galileo (3×10^-12 τ^-1/2) with a sufficient margin to guarantee the industrialization of the clock.