Use of two-photon absorption in a photorefractive crystal for three-dimensional optical memory

We describe the use of two-photon absorption in a photorefractive crystal for recording bit data in multilayered optical memory. A short-pulse near-infrared laser is used for generating the photorefractive effect by two-photon absorption. We succeeded in recording and reading seven layers of data in a LiNbO(3) crystal with a lateral resolution (distance between bits) of 5microm and an axial resolution (distance between layers) of 20 microm .