We propose a concept of holographic data storage which promises storage capacities of more than 100-Gbyte on a digital versatile disk (DVD)-sized disk. The information is stored bitwise in form of microscopic reflection holograms. High storage densities can be achieved by combining multiplexing methods and multilayer storage. A theoretical model for microscopic reflection holograms generated by focused Gaussian beams is proposed. Experimental results are presented for the recording and characterization of microholograms in DuPont's HRF-800 photopolymers. The local distribution of the diffraction efficiency was investigated by applying a confocal scanning microscope setup. Single-color holograms with a radius of 1.8 and 12 /spl mu/m depth have been recorded. We observe a blue shift in the spectral response of the microholograms of less than 2% due to shrinkage of the polymer. In the case of threefold wavelength multiplexing, all wavelengths are clearly resolved in the spectral response having spectral width /spl Delta//spl lambda/ of less than 10 nm (FWHM). Baking the holograms for 1 h at 120/spl deg/C nearly doubted the diffraction efficiency while the spectral response of the microholograms broadened by a factor two. We showed that 80-ps pulses are sufficient for holographic recording in the photopolymers. An optimized pre-illumination allows a significant increase in diffraction efficiency.
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