Abstract
Two-dimensional (2D) optical lattices of driven cold atoms can provide a useful platform to construct 2D electromagnetically induced grating (EIG) with parity-time () antisymmetry. This atomic grating is achieved by the spatial modulations of the atomic density and frequency detunings in the four-level double- atomic system. Gain-assisted antisymmetry allows us to realize lop-sided Raman–Nath diffraction with high diffraction efficiency at the exception point. It is shown that the nontrivial phenomenon originates from non-Hermitian degeneracy of antisymmetry. Our scheme may provide the possibility for active all-optical control and conversion of the spatial beam in optics.
© 2019 Optical Society of America
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