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 ($\mathcal{PT}$) antisymmetry. This atomic grating is achieved by the spatial modulations of the atomic density and frequency detunings in the four-level double-$\mathrm{\Lambda }$ atomic system. Gain-assisted $\mathcal{PT}$ 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 $\mathcal{PT}$ 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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