New concept of miniature optically pumped cesium beam frequency standards with a multiwavelength cylindrical cavity

We developed an optically pumped cesium beam resonator based on a cylindrical cavity meeting the requirements of frequency stability in the range 10^-11 τ ^{- 1}2 /, compactness, lifetime and low cost, for telecom applications. It is named PHACS which means Probatoire d´Horloge Atomique Compacte Simplifiee. We demonstrated that the TE₀₁₂ cylindrical cavity is the best choice. The interaction length is equal to 90 mm. The configuration of the microwave field in the cavity requires a longitudinal static magnetic field, created by a solenoid which surrounds the cavity and the optical regions dedicated to the state preparation and to the detection of the atoms. Constitutive elements of the resonator are designed with a cylindrical symmetry. The resonator is operated with only one optical frequency tuned to a transition in the D1 line of the cesium atom. The main drawback of the cavity is the distributed phase along the atomic path. To control this problem, we implemented an original magnetic coupling which enables us to control any asymmetry between the two cavity lobes. The main features of the resonator PHACS are: a volume of 1.8 dm³, a line-width of 2.2 kHz and a signal to noise ratio of 10,000 in a 1Hz bandwidth. The short term frequency stability is 1.2 10^-11 τ ^{- 1}2 / from 1s to 10,000s. The relative frequency offset is 2.5 10^-12 from TAI.