Patent ID: 6201821
Filing Date: 2001-03-13
Classification: G04F

Abstract:
A frequency standard, comprising:a source of incident electro-magnetic radiation including:main frequency components at frequencies of .OMEGA..sub.1 and .OMEGA..sub.2, andadditional frequency components collectively having a spectrum;a quantum absorber arranged to receive the incident electro-magnetic radiation, and having transitions including a first transition between a first lower quantum state and an upper guantum state, and a second transition between a second lower guantum state and the upper quantum state, the first transition and the second transition having energies that correspond to frequencies of .omega..sub.1 and .omega..sub.2, respectively, equal to .OMEGA..sub.1 and .OMEGA..sub.2, respectively, the lower quantum states differing in energy by an energy difference, the energy difference being subject to a total a.c. Stark shift induced by the incident electro-magnetic radiation, the total a.c. Stark shift having an intensity-dependent magnitude;a defector arranged to receive electro-magnetic radiation from the quantum absorber and generating a detection signal in response thereto;a frequency difference controller that controls the source to generate the main frequency components with a difference in frequency that obtains an extremum in the detection signal, the extremum indicating that the difference in frequency corresponds to the energy difference;a frequency standard output that provides a frequency standard signal related in frequency to the difference in frequency; anda spectrum controller that sets the spectrum of the additional frequency components to reduce the magnitude of the total a.c. Stark shift, and, hence, to increase accuracy and stability of the frequency standard signal.