Dynamics of holographic recording with focused beams in iron-doped lithium niobate crystals

Holograms are recorded with focused beams in an iron-doped lithium niobate crystal. The diffraction efficiency shows a maximum after several seconds of recording, unlike in the case of writing with two homogeneous plane waves in the same crystal. This behavior can be attributed to a compensation field caused by incomplete illumination of the crystal. The field finally stops the bulk photovoltaic effect, which is the main driving force of the process. Based on this assumptions, we derive an analytical expression for the evolution of the diffraction efficiency which correctly fits the experimental data.