Coherent And Nonlinear Phenomena In Atomic Vapor

The interaction between light and matter is one of the most fundmental fields in physics. Although it has been explored for more than a century, this field still surprises us frequently. Many novel and important phenomena have been reported. And the matrimony between this field and other field in physics opens many new directions for future research.The topic of this dissertation is about the coherent and nonlinear phenomena in atomic vapor and their potential applications. It is organized into two parts. Five works are presented in the first part. They are,1) Two photon absorption in atomic vapor and optical pumping assisted electromagnetically induced transparency. All-optical switching is a critical technology in optical communication and all-optical computation. A proposal of an all-optical switching scheme based on the two-photon absorption effect has drawn many researcher's attentions. Experimental demonstrations of this scheme in cold atoms have been reported. However no experimental result is reported in hot atomic systems. So we did an experiment that demonstrates this absorptive photon switching by quantum interference in hot atomic vapor. We found that due to the influence of Doppler broadening, the result was not as dramatic as it in cold atoms. We made some adjustments and discovered a new phenomenon that could be used to improve all-optical switching. We call it optical pumping assisted EIT. Unlike the scheme of Harris and Yamamoto, our scheme is unaffected by Doppler broadening. This phenomenon is essentially Doppler free and is insensitive to the misalignment of the optical pumping filed. Further more due to the good signal to noise ratio, this phenomenon could find applications in precise spectroscopy and laser frequency stabilization.2) Electromagnetically induced absorption without transfer of coherence. As the counter part of electromagnetically induced transparency (EIT), Electromagnetically induced absorption (EIA) draws many researcher's attentions. The origin of EIA was theoretically explained as the consequence of transfer of atomic coherence between degenerate excited states and degenerated ground states. However this is not the only mechanism for this effect. We did an experiment and observed EIA without atomic coherence transfer. We will show that in our experimental configuration there is no coherence transfer. This experiment indicates there are still other mechanisms for this effect.