| In this work we present the results of experimental observations of Landau-Zener tunneling in hexagonal photonic lattices optically induced in photorefractive crystal. Because of the fixed length of periodic media we trace the dynamics of the propagating beam by changing the input tilt angle of the probe Gaussian beam, i.e. its initial position in Fourier space relative to the high-symmetry resonance points in the first Brillouin zone. We realised in experiment two distinct cases of the three-fold resonance, symmetric and asymmetric. In both cases we observe the oscillatory character of resonant transitions by measuring the relative powers of the output beams in the far-field (reciprocal space) against input angle. The results of experiments are corroborated with semi-analytical theory based on corresponding Landau-Zener-Majorana systems as well as with numerical simulations employing anisotropic photorefractive model. |
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