Micrometer-sized reflection holograms can be written into a rapidly rotating homogeneous photopolymer disk at the focus of a high-numerical-aperture beam and its retroreflection to implement high-capacity multilayer digital data storage. This retroreflection is generated by an optical system with positive unity magnification to ensure passive alignment of the counterpropagating beam. Analysis reveals that the storage capacity and transfer rate of this bit-based holographic storage system compare favorably with traditional page-based systems but at a fraction of the system complexity and cost. The analysis is experimentally validated at 532 nm by writing and reading 12 layers of microholograms in a 125-microm photopolymer disk continuously rotating at 3600 rpm. The experimental results predict a capacity limit of 140 Gbytes in a millimeter-thick disk or over 1 Tbyte with the wavelength and numerical aperture of Blu-Ray.
Continuous wave (cw) operating temperature of 223 K was achieved with molecular beam epitaxy grown separate confinement buried heterostructure (SCBH) PbTe diode lasers with PbEuSeTe electrical and optical confinement layers. This is the highest cw operating temperature reported for midinfrared diode lasers. The active region of the SCBH diode lasers varies laterally to form a crescent-shaped waveguide with a maximum thickness of 0.15 μm and a lateral width of 2 μm. Exceptionally low threshold currents of 102 mA at 200 K, 166 mA at 210 K, and 249 mA at 215 K were measured.
A 15 mA dc H Ϫ multicusp source has been developed for injection into a TR30 cyclotron. This source is also used with a 900 kV tandem accelerator to obtain 10 mA protons at 1.8 MeV. The program is an extension of the 5-7 mA dc H Ϫ cusp source developed at TRIUMF during [1989][1990]. Major efforts include the search for the optimal filament materials, shape, and location; comparison of cusp line confinement and magnetic filtering of electrons at the extraction region; optimization of extraction lense configuration; and upgrading of vacuum and power systems capability. The source is noncesiated and the maximum arc power available is only 5 kW. After the H Ϫ beams pass through an electron suppression grid and a 20 mm collimator, we obtained 15 mA with 0.66 mm mrad 4 rms normalized emittance. At this output the e/H ratio was about 4. The best normalized emittance occurs around 5-7 mA, having a value of 0.37 mm mrad. Further development in the near future is planned using cesium and multiple apertures in the hope of increasing dc H Ϫ currents to 30 mA while holding the normalized emittance below 0.75 mm mrad.
Conventional error-correction coding techniques can be used to reduce the minimum signal-to-noise ratio required for achievement an acceptable bit-error rate and can therefore be used to increase the maximum number of pages that can be stored in a photorefractive memory. Because error-correction bits will exact some cost per page in terms of memory capacity, we address the question of when the gain in capacity surpasses this cost. It is found that a factor-of-2 improvement in capacity can be readily achieved.
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