Exploring New Approaches To Coherent Population Trapping Atomic Frequency Standards

Miniature passive atomic frequency standard based on CPT resonance has been drawing more and more attentions in the fields of GPS, underwater navigation, unmanned vehicles, etc. This work focused on improving frequency stability of the CPT atomic frequency standard, and we have mainly carried out the study through two approaches:to reduce CPT signal linewidth by combining the CPT resonance with Ramsey separated oscillating fields in time-domain, and to improve the contrast of CPT signal with the lin⊥lin CPT configuration. We have obtained several research achievements as follows:1. We have implemented the scheme of two laser pulses Ramsey-CPT interference based on a VCSEL, our results reveal that it is possible to construct a compact Ramsey-CPT atomic frequency standard.2. We have studied the multi-pulse Ramsey-CPT interference, proposed and studied a novel pulses scheme. With the obtained multi-pulse Ramsey-CPT interference signal, we can quickly and accurately identify the discriminator signal and lock the clock. Our study results reveal that it is a simple and efficient locking method for the low-cost clock.3. We have studied the microwave on/off modulation on a VCSEL to produce equivalent laser pulses by electronic method, and have realized the Ramsey-CPT interference. From the study result we have developed a practicable method for the miniature Ramsey-CPT atomic frequency standard.4. We have proposed and studied a method of time divided modulation-demodulation scheme, which can be used to lock the laser frequency and the output frequency standard of the Ramsey-CPT atomic frequency standard based on a VCSEL5. We have developed a bichromatic laser system which utilizes high diffraction orders of an AOM output, it is a cheap and feasible approach to generate highly coherent bi-chromatic light field suited for EIT experiments. With the realized laser system, we have obtained CPT signal with contrast up to30%in the lin⊥lin CPT configuration.6. We have developed a quasi-bichromatic laser system with two VCSELs working in the master-slave sideband injection-locking configuration. With the small, cheap and low power consumption system, we have obtained CPT signal with contrast up to60%in the lin⊥lin CPT configuration. This technological breakthrough overcomes a main obstacle for realizing high performance miniature CPT atomic frequency standard. Based on this method, the performance considerably improved miniature CPT atomic frequency standard could be expected.The results of our research show that with the methods we proposed and realized, the frequency stability of CPT atomic frequency standard can reach the level of4×10-12τ-1/2, about ten times as stabilized as the present available product. The same amount of improvement could also be expected in the miniature CPT atomic frequency standard with our methods.