D. H. Olson

Interaction of metal particles with adsorbed dye molecules: absorption and luminescence.

Absorption, luminescence, and excitation luminescence studies of dye molecules adsorbed onto ultrathin, variable-thickness silver films show strong coupling of the particle plasma resonances to the molecules. Luminescence from the dye is increased by excitation transfer from the silver particles for certain film thickness. Increased luminescence has also been observed from dyes on Au and Cu films.

Four-wave mixing in semi-insulating InP and GaAs using the photorefractive effect

The photorefractive effect has been observed for the first time in semi‐insulating InPe:Fe and GaAsCr. These materials are sensitive and versatile recording media for high bit rate parallel optical processing in the 0.8–1.8‐μm spectral region using injection lasers of milliwatt power levels.

Photorefractive properties of doped cadmium telluride

The first study of the photorefractive properties of doped CdTe has demonstrated high sensitivity for optical processing applications. Of the binary II‐VI and III‐V semiconductors, CdTe has the highest electro‐optic coefficient r41 in the infrared, some three times larger than that of GaAs and InP. Deep levels introduced into CdTe exhibit appropriate absorption and photoconductivity at 1.06 μm by doping with V and Ti impurities. Photorefractive beam coupling experiments in CdTe:V gave small signal gains of 0.7 cm−1, and diffraction efficiencies with no applied electrical field of 0.7%. Thus, CdTe appears to be superior to previously studied III‐V semiconductors, in the near‐infrared spectrum. Optimization of doping and trap densities is expected to result in gain which exceeds the absorption loss, thereby allowing phase conjugation with infrared injection lasers.

Cr‐doped GaAs/AlGaAs semi‐insulating multiple quantum well photorefractive devices

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.

Relationship between surface-enhanced Raman scattering and the dielectric properties of aggregated silver films

By using an evaporated silver film that has a continuously varying thickness, we have demonstrated the dependence of surface-enhanced Raman scattering (SERS) on the dielectric properties of the film. These results support local field models that are based on metal-particle resonances for SERS.

High sensitivity optical image processing device based on CdZnTe/ZnTe multiple quantum well structures

We present results on the operation of a high sensitivity semi‐insulating multiple quantum well device for optical image processing. This device operates in the visible spectrum using II‐VI CdZnTe/ZnTe multiple quantum well structures. Incident light creates charge carriers that screen an applied ac electric field modulating the absorption and refractive index of the structure through the quantum confined Stark effect. In this way, an incident intensity pattern is recorded as an absorption and refractive index variation. The semi‐insulating nature of the material eliminates the need for pixelation. In a wave‐mixing experiment, a peak diffraction efficiency of 0.25% was observed from 2.25 μm active layer of the device. Two‐beam‐coupling gain coefficients of ∼500 cm−1 at wavelengths longer than the exciton absorption peak should be possible.

Resonant photodiffractive four-wave mixing in semi-insulating GaAs/AlGaAs quantum wells.

We have performed photodiffractive four-wave mixing in semi-insulating multiple GaAs/AlGaAs quantum wells at a wavelength of 0.83 microm. The quantum wells were made semi-insulating by proton implantation, which introduces defects that are available to trap and store charge during holographic recording. The experiments demonstrate how photodiffractive behavior using the large resonant nonlinearities of quantum-confined excitons yields highly sensitive material for optical image processing. When pump powers of 1 mW/cm(2) are used, the measured sensitivity is 2 orders of magnitude greater than that of bulk, nonresonant photorefractive semiconductors.

Room‐temperature optically pumped Cd0.25Zn0.75Te/ZnTe quantum well lasers grown on GaAs substrates

Optically pumped lasers emitting near 600 nm at room temperature have been fabricated for the first time in Cd0.25Zn0.75Te/ZnTe superlattices grown on GaAs substrates. The threshold pump intensity using pulsed 0.53 μm radiation increased from ∼7 kW/cm at 10 K to ∼60 kW/cm2 at room temperature with a threshold temperature dependence described by T0∼111 K.

Photochromic gratings in photorefractive materials.

The steady-state and dynamic behavior of absorption and phase gratings in semi-insulating GaAs and InP have been studied by four-wave mixing. These measurements permit independent study of the space-charge-field screening kinetics and free-carrier recombination kinetics in these materials. The study is important both for the design of optimized materials for photorefractive applications and for the characterization of the defect electronc structure in these materials.

High-speed photodiffractive effect in semi-insulating CdZnTe/ZnTe multiple quantum wells.

Single-pulse and cw measurements of the response of a semi-insulating CdZnTe/ZnTe multiple-quantum-well photorefractive device are presented. In single-pulse experiments, photodiffractive (absorption) gratings have been written with less than 1.8-microJ/cm(2) incident fluence, and a diffraction efficiency of 1.1% is obtained from the 1.56-microm active layer of the device. With an optimized structure, the ultimate response time of the device can be below 100 ps. In cw measurements a maximum diffraction efficiency of 1.35% is obtained.