A laser light source for high-resolution near-field optics applications with an output power exceeding 1 mW (104 times the power from previous sources) and small (300 nm square to less than 50 nm square) output beam size is demonstrated. The very-small-aperture laser (VSAL) tremendously expands the range of applications possible with near-field optics and increases the signal-to-noise ratios and data rates obtained in existing applications. As an example, 250-nm-diam marks corresponding to 7.5 Gb/in.2 storage density have been recorded and read back in reflection and transmission on a rewritable phase-change disk at 24 Mb/s with a 250-nm-square aperture VSAL. VSALs potentially enable data storage densities of over 500 Gb/in.2 (up to 100 times today’s magnetic or optical storage densities).

We have for the first time demonstrated two-beam coupling energy transfer at a wavelength of 1.5 μm. Beam coupling gain coefficients of 0.6 cm−1 have been obtained in vanadium -doped CdTe with only 5 mW/cm2 incident intensity. These gain coefficients exceed typical gain coefficients in GaAs at 1.06 μm wavelength by 50%. In preliminary measurements using the moving grating technique, we have measured a gain coefficient of 2.4 cm−1. Through adjustment of the doping level, CdTe:V can be used as a sensitive photorefractive material through the 0.9–1.5 μm spectral range.

We report time-to-space mapping of femtosecond light pulses in a temporal holography setup. By reading out a temporal hologram of a short optical pulse with a continuous-wave diode laser, we accurately convert temporal pulse-shape information into a spatial pattern that can be viewed with a camera. We demonstrate real-time acquisition of electric-field autocorrelation and cross correlation of femtosecond pulses with this technique.

Room temperature excitonic absorption in CdZnTe/ZnTe quantum wells: Contributions to exciton linewidth

At wavelengths close to the band edge, strong photorefractive gratings using the Franz–Keldysh electrorefractive effect can be written in semiconductors. Two-beam-coupling exponential gain coefficients as high as Γ=16.3 cm−1 have been obtained in GaAs by combining the electrorefractive photorefractive grating with the conventional electro-optic photorefractive grating and using the moving grating technique to enhance the photorefractive space-charge field. A method for calculation of the gain coefficient near the band edge of materials is presented. The method is applied to GaAs and the results are compared to the experimental data. Reasonable agreement with experiment has been achieved. An optimal spectral range (910 nm<λ<930 nm) for near-band-edge photorefractivity in GaAs has been found. Conventional theories of photorefractivity based on Kukhtarev’s equations are found to be sufficient for calculation of the photorefractive space-charge field near the band edge. Predictions of the gain coefficient near the band edge using the moving grating technique are presented. Other methods of increasing the photorefractive gain such as the temperature-dependent resonance in InP:Fe are also discussed.

The photorefractive effect in semi-insulating Cr-doped GaAs as measured by the beam coupling technique was investigated as functions of temperature (295–386 K) and intensity (0.15–98 mW/cm2 of 1.15 μm light beams from a He-Ne laser). Results show that the photorefractive effect deteriorates rapidly over a narrow range of temperature as temperature rises and that this characteristic temperature increases with the logarithm of beam intensity. The observed phenomenon is attributed to the competing effects of the dark- and light-induced conductivities.

Semi-insulating multiple quantum well photorefractive devices using GaAs/Al0.29Ga0.71As with an electric field applied perpendicular to the layers are demonstrated. Semi-insulating behavior is obtained by doping with Cr(1016/cm3) during epitaxial growth of the material. Diffraction efficiencies as high as 3% with an applied voltage of 20 V and microsecond response times are obtained in a 2 μm thick device. These devices are of importance for implementation of fast and sensitive two-dimensional optical information processing systems at wavelengths compatible with current diode lasers without the spatial-bandwidth limitations of thick photorefractive materials.

Volume holographic gratings are written with ultraviolet light in high-optical-quality, commercially available Ge-doped silica films and in Ge-doped optical-fiber preform sections loaded with molecular hydrogen. In the film samples, peak refractive-index changes exceeding 10(-2) and a sensitivity (index change/absorbed energy density) of 0.4 × 10(-7) cm(3)/J are measured. Angular multiplexing of up to 51 gratings is demonstrated in the preform samples.