The Improved Schemes And The Related Researches On The Coherent Population Trapping Atomic Clocks

The coherent population trapping(CPT)atomic clock with a vertical cavity surface emitting laser(VCSEL)as the light source has the advantages of small volume and low power consumption.The CPT atomic clock can realize miniaturization and chip in combination with microelectromechanical systems(MEMS)fabrication techniques.That is advantageous for applications in small equipment such as portable mobile devices,GPS receivers,and small underwater communication devices.The prevailing scheme of the CPT atomic clock widely uses a single circularly polarized light to interact with alkali metal atoms,and the narrow-linewidth CPT signal is extracted from the transmitted light to stabilize the output frequency of atomic clocks.The scheme exists the spin polarized trap state which reduces the atomic utilization rate,the strong useless background signal and the strong laser noise.These effects will reduce the quality of the CPT signal and affect the enhancement of the short-term frequency stability of the CPT atomic clock.To solve these problems,this paper explored new schemes of the CPT atomic clock and carried out the related research to improve the short-term frequency stability of the CPT atomic clock under the premise of small volume and low power consumption of the CPT atomic clock.The main research contents are as follows:(1)Proposed and researched a magneto optic rotation scheme of the CPT atomic clock.Through the semi-classical theoretical derivation,the influence of the amplitude,the linewidth and the q value of the MOR-CPT signal with the magnetic field and the electric field intensities of the bichromatic light was researched.The short-term frequency stability of the miniaturized MOR-CPT atomic clock was estimated.The results showed that the short-term frequency stability of the miniaturized MOR-CPT atomic clock can be increased by more than one order of magnitude compared with the general miniaturized lin//lin CPT atomic clock.(2)Proposed and researched an elliptically polarized scheme of the CPT atomic clock.Through the semi-classical theory,the analytical expressions of the amplitude and the linewidth of the EP-CPT signal were derived.The short-term frequency stability of the chip EP-CPT atomic clock was obtained by the EP-CPT experiment.The results showed that the short-term frequency stability of the chip EP-CPT atomic clock can be increased by more than two times compared with the chip CPT atomic clock of which the scheme uses a single circularly polarized light with the same volume and power consumption.(3)Proposed and researched a scheme of the MOR Ramsey-CPT atomic clock.Through the semi-classical theory,the analytical expression of the MOR Ramsey-CPT signal was obtained by solving the corresponding density matrix equations.The relevant experimental system was set up to obtain the MOR Ramsey-CPT signal in the experiment and compared with the theoretical calculation results.The relation of the amplitude,the linewidth and the q value of the MOR Ramsey-CPT signal with the magnetic field and the free evolution time was researched.The results showed that the signal obtained by experiment basically coincides with the signal calculated by using the analytical expression,and the analytical expression calculated in theory can be correctly applied to describe the MOR Ramsey-CPT scheme.