Characteristic Study And Scheme Exploration Of CPT Atomic Clock Physics Package

At Present all kinds of new type atomic clocks have rapidly developed, especially miniature passive atomic clock based on coherent population trapping (CPT) has attained more and more attentions. Different CPT atomic clock schemes have been proposed and studied, and the compact and chip-scale CPT atomic clock products have been realized in the United States. This thesis mainly includes that work in the implementation of CPT atomic clock engineering transformation and theoretical and experimental researches to improve the performance of CPT atomic clock. The main research achievements are as follows:We have made a contribution to the engineering transformation of CPT atomic clock. To implement engineering transformation of physics package, our contribution is testing performances of the vertical cavity surface emitting laser (VCSEL), including its polarization mode, light-emission behavior etc, and eventually choosing the suitable VCSEL for implementation of the CPT atomic clock product; measuring and studying the amount of rubidium in atomic vapor cell, and determining the amount of rubidium which shall be filled in an atomic vapor cell. According to the design of the physics package, we have designed a special magnetic field coil by applying Helmholtz coils, which has been chosen for the CPT atomic clock. We also have formulated design and process documents. The CPT atomic clock, which is done engineering transformation, has been produced in small batch.We have theoretically studied CPT resonance from different configurations. The objects studied include double A configurations with co-propagating left--right (σ+-σ-) circularly polarized lasers, double A configurations with orthogonal polarized (lin⊥ lin) lasers, double A configurations with parallel linearly polarized (lin//lin) lasers and four-wave mixing (FWM) and so on. We have compared different configurations about the effects of eliminating spin-polarized dark state, improving the linewidth and amplitude of CPT resonance signal, and also obtained the characteristics and advantages of the schemes.We have made experimentally study of buffer gas N2 on the CPT resonance signal produced with 85Rb with a glass bulb filled with 85Rb and N2. In the experiment N2 is used as buffer gas, we have detailed studied the dependences of CPT resonance signal on the pressure of buffer gas, including frequency shift, linewidth, contrast and correction slope etc. Our study results reveal that using N2 as buffer gas has certain advantage in CPT atomic clock with 85Rb as working atom.We have proposed and studied a scheme of optically pumping 87Rb with co-propagating σ+-σ- circularly polarized lasers. The preparation of CPT state is resonantly enhanced with both σ+ and σ- lasers simultaneous interacting with atoms by means of polarization reflection and phase delay by changing the optical path length. With eliminating spin-polarized dark state in CPT state preparation, we have obtained CPT resonance signal 3 times larger than that of the conventional scheme used in atomic clock in the same condition.We have made a study of lin⊥lin quasi-bichromatic laser system by the master-slave injection locking configuration with an external-cavity diode laser (ECDL) as the master and a microwave modulated VCSEL as the slave. With the narrow linewidth laser from a ECDL, whose frequency is stabilized by a Doppler-free spectral line, we inject the laser into a microwave modulated VCSEL to inject lock its 1st sideband to realize a lin⊥lin quasi-bichromatic laser output. We have experimentally compared our originally realized lin ⊥ lin quasi-bichromatic laser with two VCSELs working in the master-slave locking configuration by generating CPT resonance. The knowledge from the experimental comparison provide important reference value for choosing right lin⊥lin quasi-bichromatic laser according to specific application.