Nondestructive readout of holograms in iron-doped lithium niobate crystals

A study was made of the possibility of holographic recording of data in LiNbO₃:Fe crystals and of their readout with light of different wavelengths so as to avoid optical erasure. The holograms were recorded using light of wavelengths λ = 0.44 and 0.63 μ and read out with light of wavelengths λ = 0.69, 0.9, and 1.06 μ. There was no erasure when readout light of the wavelength λ = 1.06 μ and power density 30 W/cm² was used for one hour. Measurements of the diffraction efficiency of the same hologram at different wavelengths indicated that the photorefraction effect was independent of the readout wavelength. An experimental study of the recording and readout of Fourier holograms of transparencies at different wavelengths demonstrated that all the recorded data could be recovered by varying the angle of incidence of the readout beam.