We demonstrate a method to experimentally calibrate the refractive index modulation in photorefractive lattices, a task rarely addressed that is crucial for quantitative comparisons of theories with experiments. We consider the linear propagation of a normally incident plane wave through simple lattices and its modulation amplitude at crystal output face. Finding no evidence of longitudinal (Talbot-like) oscillations, we discard an ideal propagation theory and construct a simple effective model that includes longitudinal relaxation. We obtain calibrations of 1D and 2D lattices consistent with standard theory in a high saturation regime. For 2D lattices, we find anisotropies χ = 1.5 − 2.5, stronger for smaller lattice period, and refractive indexes larger than for 1D lattices, also with more noise. Technol. 14, 423-428 (1996). 12. R. Magnusson and T. Gaylord, "Use of dynamic theory to describe experimental results from volume holography," J. Appl. Phys. 47, 190-199 (1976 oscillations are faster, we expect even stronger damping effects. 31. We take into account the finite resolution of our imaging system by convoluting the profiles given by the effective theory by a gaussian optical response of r.m.s width σ 0 = 0.80µm.

We study experimentally the writing of one-and two-dimensional photorefractive lattices, focusing on the often overlooked transient regime. Our measurements agree well with theory, in particular concerning the ratio of the drift to diffusion terms. We then study the transverse dynamics of coherent waves propagating in the lattices, in a few novel and simple configurations. For focused linear waves with broad transverse spectrum, we remark that both the intensity distributions in real space ("discrete diffraction") and Fourier space ("Brillouin zone spectroscopy") reflect the Bragg planes and band structure. For non-linear waves, we observe modulational instability and discrete solitons formation in time domain. We discuss also the non-ideal effects inherent to the photoinduction technique : anisotropy, residual nonlinearity, diffusive term, non-stationarity.

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