|M.Sc Student||Yotam Zohar|
|Subject||The Effects of Repumping on EIT Resonance|
|Department||Department of Physics||Supervisors||Professor Emeritus Ron Amiram|
|Dr. Amnon Fisher|
|Full Thesis text|
Electromagnetically induced transparency (EIT) occurs when two nearly resonant light fields excite two ground-state sub-levels to a single upper level. The simultaneous interaction of the two light fields traps the atom in a coherent super-position of the ground-state and prevents its excitation to the upper level. This allows the light beam to pass the medium, which otherwise would have been completely opaque - i.e. transparency induced by an electromagnetic field. A striking feature of this phenomenon is that the induced transparency is extremely sensitive to the frequency difference of the light fields, resulting in ultra-narrow spectroscopic features (EIT lines) along with strong dispersion. We present a study on the physical processes that govern the spectral width and contrasts of EIT resonances in room temperature vapor.
Initially, we carefully study the depopulation rates within the ground state sub-levels of 87Rb vapor, and find the dominant physical processes that govern the decay of the coherence: diffusion and spin-exchange. By applying an additional repump beam we optically pump the medium, overpopulating the sub-level with maximal angular momentum ('end-state'), and strongly polarizing the medium. The polarized medium is found to be more resistant to decay, since end-state interactions are spin-exchange resistant.
Finally, we study the effect of introducing the repump beam on the EIT spectrum of the medium. We construct an EIT state with most of the population in the end-state - 'end-state-like EIT'. This state experience reduced spin-exchange related decoherence, and hence a narrower line-width. Moreover, by optically pumping spectator levels, the population in the active EIT levels is increased, improving the contrast of the EIT resonance.