Abstract
We propose and analyze an efficient scheme for the lopsided Raman-Nath diffraction of one-dimensional () and two-dimensional () atomic gratings with periodic parity-time ()-symmetric refractive index. The atomic grating is constructed by the cold-atomic vapor with two isotopes of rubidium, which is driven by weak probe field and space-dependent control field. Using experimentally achievable parameters, we identify the conditions under which -symmetric refractive index allows us to observe the lopsided Raman-Nath diffraction phenomenon and improve the diffraction efficiencies beyond what is achievable in a conventional atomic grating. The nontrivial atomic grating is a superposition of an amplitude grating and a phase grating. It is found that the lopsided Raman-Nath diffraction at the exceptional point (EP) of -symmetric grating originates from constructive and destructive interferences between the amplitude and phase gratings. Furthermore, we show that the -phase transition from unbroken to broken -symmetric regimes can modify the asymmetric distribution of the diffraction spectrum and that the diffraction efficiencies in the non-negative diffraction orders can be significantly enhanced when the atomic grating is pushed into a broken -symmetric phase. In addition, we also analyze the influence of the grating thickness on the diffraction spectrum. Our scheme may provide the possibility to design a gain-beam splitter with tunable splitting ratio and other optical components in integrated optics.
3 More- Received 4 September 2017
DOI:https://doi.org/10.1103/PhysRevA.97.033819
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