Recording of a hologram by using the second-order nonlinearity

A new method of cross correlation of wave fronts by means of the so-called second-harmonic generating hologram (SHG-hologram) is considered. An interference pattern of the object and reference waves is recorded by this method in a nonlinear light-sensitive material characterized by the second-order nonlinearity. The hologram obtained in this way generates a wave at the doubled frequency, which forms the reconstructed image without any delay at the instant of time when the interfering wave fronts traverse the light-sensitive material. An expression determining the electric field of the wave reconstructed by the hologram is obtained. On the basis of this expression, a graphic method for constructing the wave front reconstructed by the hologram is developed. It is shown that the transverse dimensions of the image reconstructed by a SHG-hologram are equal to the transverse dimensions of the object being recorded, and the longitudinal dimensions are doubled. It is shown that changes in the position of the reference source also result in changes in the position and scale of the reconstructed image. It is proposed to use the properties of the SHG-hologram to create a system of switchable interconnections, which operate on the "controlling light by light" principle. The scheme of an element of such a system is proposed and considered. The experimental recording of the SHG-hologram was carried out. This hologram was recorded in a barium berate (BBO) crystal with the help of a Nd:YAG laser. The experiment verified the capability of SHG-hologram to form the image with a high resolution. This experiment also confirmed the dependences of the scale and position of the reconstructed image on the wavelength of the generated radiation and the position of the reference source. (C) 2000 MAIK "Nauka/Interperiodica".