Patent ID: 6320472
Filing Date: 2001-11-20
Classification: G04F,H03L

Abstract:
An atomic frequency standard comprising:(A) a cell containing an admixture of alkali metal atoms and a mixture of buffer gases non reactive with said alkali metal atoms, said mixture being selected to minimize the temperature coefficient within said cell;(B) at least one laser to excite said alkali metal atoms within said cell into resonance, light output of each said laser being of a wavelength corresponding to either of (a) D.sub.1 or (b) D.sub.2 transition of said alkali metal atoms, each laser's frequency being modulated by a rf generator over a frequency range including a subharmonic of a hyperfine ground state 0-0 transition frequency of said alkali metal atoms, thereby to achieve the phenomenon of Coherent Population Trapping whereby ground state populations of the resonant alkali metal atoms remain unaltered;(C) a photodetector connected to detect at least one of (a) fluorescence of the laser excited alkali metal atoms within said cell or (b) light transmitted through said cell and produce a signal responsive thereto;(D) a frequency control loop connected to receive said signal and, responsive thereto, to lock said rf generator to said hyperfine ground state frequency; and(E) a frequency control loop to receive said signal and, responsive thereto, to lock each said laser to the optical resonance line of said alkali metal atoms.