High-resolution Noise Spectrum Based On Atomic Coherence Effects

The interaction between light and matter is the physical basis for the birth of the laser, as well as precondition for the vigorous development of quantum optics. In recent years, being an important branch of quantum optics, the interaction between light and atoms has been developed rapidly. The atomic coherence induced by the interaction between light and atoms will play an important role in the development of quantum information in future due to its applications in quantum memroy and quantum communication, and thus attract more attention. The electromagnetically induced transparency, which can reduce the absorption of the probe field and enhance the dispersion, is usually used to control the group velocity, realize quantum memory, reduce quantum noise, enhance the nonlinearity effect in vicinity of resonance, and so on.In this thesis, the atomic coherence effects of coherent population trapping, electromagnetically induced transparency and electromagnetically induced absorption are firstly reviewed. And then, the atomic coherence effect in degenerate two-level atomic system is investigated. The interaction between the arbitrary angular momentm of ground and excited states and the arbitrary intense and polarization pumping field is theoretical presented, and based on the theoretical model, the absorption and dispersion properties of probe field for the transition Fg=1â†'Fe=0are numerically solved. On the other hand, in the rotating frame, the eigenvalues and eigenvectors of Hamiltonian are solved and discussed, giving the expression for dark state of this system in different cases. Thus the corresponding relations among the absorption, dispersion properties of probe field and the dark state in Fg=1â†'Fe=0transition atomic system are studied. Also, the comparison of atomic coherence between double Λ-type and single Λ-type system is discussed. It shows that the coherence based on the multi-ground state can be enhanced, especially for the double Λ-type system.Moreover, high-resolution noise spectrum of Cesium atoms which are based on the absorption and dispersion properties of probe field in atomic coherence are also dicussed. It is found that the resolution of amplitude noise spectrum in Cs atomic vapor can be enhanced by narrowing the absorption using velocity selective optical pumping technique due to high absorption accompanied by steep atomic dispersion, which leads to more conversion of laser phase noise to amplitude noise when the field propagates throughout the atoms. The effect of optical pumping intensity on the spectrum resolution is also discussed, and a theoretical explanation for this phenomenon is given, which shows that the phase-to amplitude noise conversion is directly proportional to the dispersion of medium. Furthermore, the phase noise to amplitude noise conversion through an electromagnetically induced transparency system is experimentally demonstrated. The experimental observations are in good agreement with the numerical calculations, which shows that EIT can be used as a method to measure laser phase noise.