Spatial amplification

We propose and demonstrate a novel image processing technique called spatial amplification where a set of selected spatial frequency components of an incident image is coherently amplified. In this technique, an incident image is first Fourier transformed onto a photorefractive crystal where it interacts with a nonuniform pump beam to selectively enhance the energy of certain spatial frequency components via two-beam coupling, 1 and is then reimaged onto an output plane. The overlap of the pump and the Fourier transformed beam inside the crystal defines the type of image processing that is performed. For example, if only the higher-order frequency components corresponding to vertical lines are amplified, the process will yield vertical edge enhancement. With this description of spatial amplification, one can readily see its similarity to the well-known technique of spatial filtering. However, because it does not remove any spatial frequency components as is common in spatial filtering techniques, there are several advantages of spatial amplification such as high energy efficiency, high dynamic range, and cascadability. In our experiments, a photorefractive BaTiO 3 crystal is used as the amplifying medium. The lack of phase crosstalk between the two interacting beams is recognized as the essential part of our technique.