Abstract: In this paper a scheme for the laser decelerated alkali metal atomic beam frequency standards is proposed. Atomic beam is decelerated and state selected simultaneously by a resonant laser beam. The velocity of the atoms in beam can be reduced to less than 10m/s. In this process the atoms will automatically get together onto a Zeeman sublevel of the ground state with maximum magnetic quantum number by the optical pumping effect. To avoid the bending of the beam trajectory by the gravity the atomic beam is deflected by a inhomogeneous magnet and goes vertically upward. Then by the method of serial magnetic resonances the atoms will transfer into m_F=0 clock sublevel. When the atoms pass twice through the single microwave cavity upward and downward by free falling in the gravity, the Ramsey resonance pattern of linewidth about ¹Hz will be produced. The signal is detected by another laser beam. The stability and accuracy of more than one or two order of magnitude comparing with the conventional atomic beam frequency standards are expected. The methods of laser deceleration and state selection, the measure for overcoming the transverse heating, the method of serial magnetic resonances and the apparatus design for obtaining the vertical beam are discussed in detail.

Key words: atomic beam, frequency Standard, laser decelerating, laser state selecting, serial magnetic resonances