Abstract: A microwave interaction module has a magnetic shield in which is created a constant magnetic field (the "C field"), an an electromagnetic cavity for generating a radiofrequency magnetic field in the path of beam of atomic or molecular particles. The electromagnetic cavity comprises a first U-shaped wave-guide, the extremities of which are provided with apertures for the passage of the beam of particles, and a second wave-guide connected electromagnetically to the first wave-guide by a connecting aperture made in the upper face of the first wave-guide. The entire electromagnetic cavity is thus within the magnetic sield and the radiofrequency signal is carried by a coaxial cable passing through this shield.

Abstract: The passive frequency standard of this invention comprises a cell (42) containing Rb87 and a source of predetermined spectral component which, by optical pumping, empties the level F=1, m.sub.F =0 and populates the level F=2, m.sub.F =0. This source comprises a lamp (40) and an isotopic filter constituted by Rb 85 contained in the cell (42). A helicoidal resonator (44) is tuned to the transition frequency between level F=2, m.sub.F =0 and level F=1, m.sub.F =0. It receives an excitation signal for stimulating such transition from an oscillator via a connector (64). The frequency of the oscillator is slaved to the transition frequency by slave means comprising a photoelectric cell (46) which receives the light from the lamp (40) through the cell (42).

Abstract: The atomic frequency standard comprises a source of light of a given spectral component, comprising a lamp 2 and an isotopic filter 3. The light arriving in an Rb 87 cell 4 empties the hyperfine level F=1 by optical pumping. Microwave excitation produced by a loop 5 causes the atoms which populated the level F=2, m.sub.F =0, to fall back to the level F=1, m.sub.F =0. Filling of the latter level reduces the transparency of the cell 4, which phenomenon is detected by a photoelectric cell 6 and permits tuning of the microwave excitation to the hyperfine transition frequency. The electromagnetic wave produced by the loop 5 is progressive, which, by the Doppler effect, increases the width of the absorption line of the cell. This increase makes it possible to reduce the control time constant and consequently makes it possible to have a compact frequency standard, with a rapid control action, which can operate in an unfavorable environment.