A three-color, solid-state, volumetric display based on two-step, two-frequency upconversion in rare earth-doped heavy metal fluoride glass is described. The device uses infrared laser beams that intersect inside a transparent volume of active optical material to address red, green, and blue voxels by sequential two-step resonant absorption. Three-dimensional wire-frame images, surface areas, and solids are drawn by scanning the point of intersection of the lasers around inside of the material. The prototype device is driven with laser diodes, uses conventional focusing optics and mechanical scanners, and is bright enough to be seen in ambient room lighting conditions. QuickTime movie of the three-dimensional display.

We have studied InAs/GaSb superlattices (SLs) grown with either InSb-like or GaAs-like interfaces (IFs) on top of a GaSb buffer layer on (100) GaAs substrates. The InAs layer thickness was varied from 4 to 14 monolayers (ML) while the GaSb layer thickness was kept fixed at 10 ML. The type of IF bonds realized was verified by Raman scattering from mechanical IF modes. High-resolution X-ray diffraction using one- and two-dimensional mapping of symmetric and asymmetric reflections allowed us to determine independently the lattice parameters parallel and perpendicular to the growth direction. The GaSb buffer layer was found to be fully relaxed whereas the SLs with InSb-like IFs were coherently strained to the in-plane lattice parameter of the GaSb buffer for InAs layer thicknesses exceeding 6 ML. The strain distribution within the SLs with GaAs-like IFs was obtained from simulations of the X-ray reflection profiles. The SLs were found to be coherently strained close to the GaSb buffer and showed increasing strain relaxation with increasing distance from the buffer layer. In addition, these simulations provide an accurate determination of the SL periods. Well-resolved Raman spectra of backfolded longitudinal acoustic (LA) phonons were observed showing for SLs with ZnSb-like IFs folded LA phonon lines up to the seventh order. The spectrum of quasiconfined optical SL phonons was examined by Raman spectroscopy and by IR reflection. A detailed analysis of the IR reflection spectra allowed an independent determination of the individual layer widths within the SL stack, including the spatial extent of the GaAs-like IF mode

Far-infrared magnetospectroscopy has been carried out on shallow donor impurities doped in the central region of GaAs quantum wells in o GaAs-Al x Gai_ x As multiple-quantum-well structures. Quantum-well widths between 80 and 450 A were investigated. Results are in very good agreement with recent effective-mass calculations for isolated impurities at the center of GaAs quantum wells.

We propose and demonstrate a novel concept for intersubband detectors at operating wavelengths of 3–5 μm using GaAs quantum wells. An extremely large intersubband spacing is obtained by using ultrathin AlAs barriers on either side of the GaAs quantum wells followed by a thicker Al0.3Ga0.7As layer. Simultaneously, the confining AlAs layers act as tunnel barriers which allow an electrical detection of the intersubband excitation.

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