Observation of optical memory in paraelectric DKDP

An image of an object in the form of a two-dimensional phase grating with a period of 0.4 mm was stored for the first time in a DKDP crystal at room temperature by pulsed neodymium laser radiation. The laser operated in the free-running regime. The threshold for detection of the photorefractive effect, discovered earlier in the same crystal, was 4 J cm^–2 at room temperature. The storage of an image was deduced from the pattern of diffraction of an He — Ne laser beam (wavelength 0.63 μm) by the phase grating. The experimental results indicated that the diffraction pattern represented a transverse distribution of the neodymium laser radiation power in the bulk of the crystal.