US 6,320,472 B1Granted

Atomic frequency standard

AssigneeKernco, Inc.

InventorJacques Vanier

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Abstract

An atomic frequency standard based on the ground state hyperfine resonance line observed by means of coherent radiation fields creating Coherent Population Trapping (CPT) in an alkali metal atomic ensemble contained in a cell. The radiation fields are created by frequency modulating a laser at a subharmonic of the hyperfine resonance frequency of the alkali atomic ensemble chosen or by using two lasers whose frequency difference is equal to the hyperfine frequency of the alkali atoms. The hyperfine resonance signal is observed either on the fluorescence emitted by the alkali atoms contained in the cell or on the light transmitted through the same cell. This signal is used, through synchronous detection, to lock the frequency of the microwave generator used to modulate the laser (or to maintain the frequency difference between the two lasers), to the hyperfine resonance frequency of the alkali atoms, thereby implementing an atomic frequency standard.

Claims18

Dependent claims

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) D1 or (b) D2 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.

3 more elements

Dependencies are inferred from the claim text.