This paper discusses the properties of a hologram recorded in a medium that possesses quadratic nonlinearity when the frequencies of the nonlinear and reference waves are identical and different. It is shown theoretically and experimentally that holograms of this type can form three-dimensional images of objects. Experiments on the recording of holograms were carried out using a pulsed Nd:YAG laser with a pulse width of 20 ns. The holograms were recorded in BBO and KTP crystals.
Yu. N. Denisyuk, "Properties of holograms recorded in a material with quadratic nonlinearity," J. Opt. Technol. 73, 429-431 (2006)