We show that electrostriction contributes significantly to self-action effects in optical fibers, adding 19% to the nonlinear refractive index for fields that vary slowly compared with the ~1-ns time scale of the acoustic response. Electrostriction also modifies the tensor nature of the nonlinear-optical response. The electrostrictive nonlinearity is the origin of the observed difference between measurements of n(2) with cw and mode-locked lasers.

The use of small apertures or sharpened tips as sensing elements in scanned-probe optical sensing devices has led to the development of a number of instruments that provide lateral spatial resolution much finer than that available in conventional optical imaging instruments. Such a device might generally be classified as a scanning optical microscope, or SOM. One particular mode of SOM operation involves the use of a sharpened optical fiber to collect light emanating from a surface. The lateral spatial resolution of such a collection-mode SOM is discussed in terms of the electromagnetic mode solutions of the probe tip. Numerical results indicate that, though bound modes solutions exist for increasingly fine unclad tips, classical diffraction effects limit resolution to a finite fraction (approximately 1/3) of the source wavelength λ. A second mechanism for signal transduction is shown to involve molecular scattering at the probe tip. An analysis of signal collection efficiency demonstrates that at tip radii below λ/5 for metallic-clad probes, and λ/10 for probes in a dielectric ambient, scattering dominates and imaging resolution scales with tip size, thus defeating limits imposed by diffraction.

The electrostrictive contribution to the nonlinear refractive index is investigated by use of frequency-dependent cross-phase modulation with a weak unpolarized cw probe wave and a harmonically modulated pump copropagating in optical fibers. Self-delayed homodyne detection is used to measure the amplitude of the sidebands imposed upon the probe wave as a function of pump intensity for pump modulation frequencies from 10 MHz to 1 GHz. The ratio of the electrostrictive nonlinear coefficient to the cross-phase-modulation Kerr coefficient for unpolarized light is measured to be 1.58:1 for a standard step-index single-mode fiber and 0.41:1 for dispersion-shifted fibers, indicating a larger electrostrictive response in silica fibers than previously expected.

Single-crystal multilayers of the dilute magnetic semiconductor Cd1−x Mnx Te (x∼0.2) alternating with CdTe have been successfully grown for the first time using the molecular beam epitaxy technique. Four sets of superlattices have been prepared consisting of 14, 60, 90, and 240 double layers of average thickness 460, 140, 75, and 37 Å, respectively. Each set consists of two samples grown simultaneously using 7×15×1-mm thick (0001) sapphire substrates onto which 5.0-μm-thick CdTe buffer layers were first deposited. X-ray diffraction techniques were employed to verify that epitaxy had been achieved and to obtain the average lattice constant of each of the multilayer structures. X-ray diffraction satellites were observed on both sides of the (111) diffraction peak of the superlattices composed of 14 and 60 alternating layers, respectively, which allowed an accurate estimate of the superlattice period, or double-layer thickness, for these samples. Results of UV reflectance studies and photoluminescence experiments at liquid nitrogen temperatures are also presented and discussed.