We demonstrate that the Hanle effect can be tuned between magnetically induced absorption (MIA) and magnetically induced transmission (MIT) simply by changing the polarization of the input laser beam. The experiments are done using closed hyperfine transitions of the D 2 line of 133 Cs -F g = 3 → F e = 2 and F g = 4 → F e = 5. The former shows a transformation from MIT to MIA, while the latter shows the opposite behavior. A qualitative explanation based on optical pumping and coherences among the magnetic sublevels of the ground state is borne out by a detailed density-matrix calculation. To increase the coherence time, the experiments are done in a Cs vapor cell with paraffin coating on the walls. The observed linewidth is extremely narrow (∼ 0.1 mG) compared to previous work in this area, making this a promising technique for all kinds of precision measurements.

We demonstrate a technique for continuous tuning of the Hanle effect from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) by changing the polarization ellipticity of a control beam. In contrast to previous work in this field, we use spatially separated probe and control beams. The experiments are done using magnetic sublevels of the Fg = 4 → Fe = 5 closed hyperfine transition in the 852 nm D2 line of 133Cs. The atoms are contained in a room temperature vapor cell with anti-relaxation (paraffin) coating on the walls. The paraffin coating is necessary for the atomic coherence to be transported between the beams. The experimental results are supported by a density-matrix analysis of the system, which also explains the observed amplitude and zero-crossing of the resonances. Such continuous tuning of the sign of a resonance has important applications in quantum memory and other precision measurements.

We demonstrate-experimentally and theoretically-that resonances obtained in electromagnetically induced transparency (EIT) can be both bright and dark. The experiments are done using magnetic sublevels of a hyperfine transition in the D 1 line of 87 Rb. The degeneracy of the sublevels is removed by having a magnetic field of value 27 G. The atoms are contained in a roomtemperature vapor cell with anti-relaxation coating on the walls. Theoretical analysis based on a two-region model reproduces the experimental spectrum quite well. This ability to have both bright and dark resonances promises applications in sub-and super-luminal propagation of light, and sensitive magnetometry.

We demonstrate laser interferometry based on phase difference between the two arms of the interferometer. The experiments are done with a Cs atomic vapor cell at room temperature and use atomic coherence. The interference can be tuned from constructive to destructive by tuning the relative phase between the two arms. It is similar to the Michelson interferometer, but differs in the important aspect of allowing interference when the polarizations in the two arms are orthogonal. This would be a novel method for interfering two independent lasers, which even can allow interfering two independent lasers of completely different wavelengths-such as of UV and IR-and also possibly phase lock them.

We demonstrate laser interferometry based on phase difference between the two arms of an interferometer. The experiments are done with a Cs atomic vapor cell at room temperature and use atomic coherence. The interference can be tuned from constructive to destructive by tuning the relative phase between the two arms. It is similar to the Michelson interferometer, but differs in the important aspect of allowing interference when the polarizations in the two arms are orthogonal. This would be a novel method for interfering two independent lasers, which can even allow interfering two independent lasers of completely different wavelengths.