Atomic coherence effects in quantum optics

The studies of several atomic effects have been presented in this dissertation. In the first part of the dissertation, I put forward a new interference means where atomic coherence is generated via incoherent pump fields. I then show that it can lead to lasing without inversion and high index of refraction with both upper- and lower-level-doublet schemes. Next, I present a theoretical and experimental investigation of the Doppler broadening and relaxational processes on the atomic coherence effects within the Na {dollar}Dsb1{dollar} manifold.; In the second part of the dissertation, I present a theoretical study of the regularly pumped micromasers (RPM). Five major issues are addressed in this part: (1) The effects of the regular pumping on the photon statistics. (2) The suitability of the master-equation approach for RPM. (3) Macroscopic and submacroscopic fields in RPM. (4) The spectrum of RPM. (5) The collective Rabi oscillation in RPM.; Finally, in part three, I present two additional topics in quantum optics. In the first topic, I discuss the influence of the Wiener-Levy laser phase noise on the resonant fluorescence intensity and spectrum. In the second topic, I give a detailed study on quantum versus stochastic or hidden-variable fluctuations in two-photon interference effects.