Physical Origin of the Frequency Shifts

When ohsewed in a cesium beum frequency standard, the hyperfine transition frequency of the atom^ differs slightEyfrom the invariant trunsition frequency of the unperturbed atoms at rest. The vurious physical and technical origins of the frequency oflets are stated, They relate to fundumentul physical eflects, to the method of probing the atomic resonance and to the frequenq control of the slaved oscillator. The vuriution of the frequency ofiets under a change o f t h value of the internal operating characteristics is considered. The sensitivity to a change of the magnetic induction, the microwuve power and the temperuture is given. A comparison is mu& of the sensitivity of cesium beam frequency stundurds of the commerciully uvailclhle type, making use of magnetic state sebction, and of devices under study, in which the stute preparation and htection is accomplished optically. T h pathwuys between t h uternal stimuli and the physical origin of the frequency ofiets are speci$ed.