An atomic frequency micrometer based on the coherent population beating phenomenon

We have demonstrated an atomic frequency micrometer based on the coherent population beating phenomenon, which enables us to obtain the beat frequency between the measured signal and the atomic transition frequency. The beat frequency and its fluctuations are detected and accurately measured through digital signal processing, which is capable of up to mHz or higher frequency resolutions (for GHz signal). The frequency discrimination via our method is comparable to that of the Ramsey fringes method, and the working range is no longer limited by the width of line shape. This enables us to achieve an atomic clock by actively compensating the frequency shift, which eliminates the need for a phase locking loop, and broadens the working range with increasing reliability. This novel scheme could be extended to the optical frequency region, implying possible future applications in optical atomic clocks, optical frequency comb, atomic spectroscopy and other related researches.