Atomic frequency standard using free induction technique
AssigneeHughes Aircraft Company
InventorHarry T. Wang
Life of this patent
Estimating the term…
Abstract
In the free induction technique of this invention, the maser is externally stimulated to allow significant reduction of the size of the maser, and the stimulation is turned off and allowed to decay so that the maser output is free from the external stimulation before the signal is sensed to provide a clock frequency standard. As a result, the invention solves significant problems which otherwise have limited the accuracy of prior art atomic clocks, including the problem of frequency pulling due to amplitude drift in the stimulation signal.
Claims21
A maser atomic frequency standard clock comprising:
- a microwave cavity;
- an oscillator generating an oscillator signal;
- an atom storage bulb in said cavity;
- means for injecting atoms of a selected magnetic spin orientation into said storage bulb;
- means for stimulating coherent emission from said atoms referenced to said oscillator signal;
- pulsing means for temporarily connecting said stimulating means to said cavity during a first time period and then disconnecting said stimulating means from said cavity for a second time period;
- means for sensing said coherent emission during said second time period exclusively, whereby said sensing means generates a maser output signal having a phase and frequency which is substantially unaffected by said stimulating means;
- means for comparing the frequency of said maser output signal with the frequency of said oscillator signal to generate a difference signal in response thereto;
- and
- means for changing the frequency of said oscillator signal so as to null said difference signal.
A method for generating an atomic clock standard frequency by free induction using an oscillator generating an oscillator signal, comprising:
- injecting atoms of a selected magnetic spin orientation into a maser cavity;
- stimulating coherent emission from said atoms for a first duration of a time by introducing a stimulating signal referenced to said oscillator signal into said cavity;
- permitting said coherent emission to freely oscillate in said cavity in the absence of external stimulation during a second duration of time;
- sensing said coherent emission during said second duration of time;
- generating a maser output signal in response to said sensing step which is substantially unaffected by the frequency or phase of said stimulating signal;
- comparing the frequency of said maser output signal with the frequency of said oscillator signal and generating a difference signal in response thereto;
- and
- changing the frequency of said oscillator signal so as to null said difference signal.
A method for reducing frequency and phase distortion in an externally stimulated maser, comprising:
- temporarily exciting atoms in said maser with external excitation;
- allowing said atoms to radiate in said maser free of any external excitation for a duration of time;
- sensing the radiation of said atoms only during said duration of time;
- and,
- generating a maser output signal in response to said sensing step which is substantially unaffected by the frequency or phase of said external excitation;
- comparing the frequency of said maser output signal with the frequency of said external excitation, said comparing step including the step of synthesizing at least one of said external excitation and said maser output signal, and generating a difference signal in response to said comparing step;
- and
- changing the frequency of said external excitation so as to null said difference signal.
Dependencies are inferred from the claim text.