  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 photo-induction technique : anisotropy, residual
nonlinearity, diffusive term, non-stationarity.
