Sukmock Lee

Ultrafast modulation with subpicosecond recovery time in a GaAs/AlGaAs nonlinear directional coupler

All‐optical modulation is observed at room temperature in a GaAs/AlGaAs multiple quantum well nonlinear directional coupler using femtosecond pulses. The origin of the ultrafast (<500 fs) recovery of the device is attributed to the optical Stark effect.

Elastic properties of epitaxial ZnSe(001) films on GaAs measured by Brillouin spectroscopy

Brillouin scattering experiments have been performed on a series of epitaxially grown ZnSe (001) films on GaAs (001) of thicknesses between 0.23 and 2.0 μm. No thickness‐dependent modifications of the elastic constants have been found. The obtained room‐temperature values of C11=87.0, C12=54.7, and C44=39.1 GPa are in good agreement with literature values of ZnSe bulk material. The calculation of the theoretical cross sections shows a good agreement with the experimental data.

Enhancement of optical nonlinearity of heavy‐metal oxide glasses by replacing lead and bismuth with thallium

We report on the results of degenerate four‐wave mixing experiments at a wavelength of 1.06 μm on a number of heavy‐metal gallate glasses. The replacement of lead (Pb) and/or bismuth (Bi) by thallium (Tl) leads to an enhancement of the optical nonlinearity, resulting in the largest nonresonant electronic nonlinearity yet reported for an oxide glass. χ(3) is proportional to the concentration of Tl; samples with more than 25 cationu2009% Tl have χ(3) larger than that of carbon disulfide (CS2). The optical nonlinearity has an off‐resonant electronic origin, which is confirmed by measurements of the diagonal and off‐diagonal components of the χ(3) tensor.

Subpicosecond switching in a current injected GaAs/AlGaAs multiple‐quantum‐well nonlinear directional coupler

We have demonstrated ultrafast switching behavior in a current injected GaAs/AlGaAs multiple‐quantum‐well nonlinear directional coupler at room temperature. The results show low crossover pulse energy (10 pJ) and full recovery within 1 ps.

Brillouin scattering studies of the elastic properties of metallic superlattices

Abstract The determination of the elastic properties of metallic superlattices using Brillouin scattering is discussed. Previous work by our group is reviewed and preliminary results for Ag/Pd superlattices are reported.

Determination of the elastic constants of a polymeric Langmuir-Blodgett film by Brillouin spectroscopy

Abstract Brillouin scattering experiments have been performed and theory developed on polymeric uniaxial Langmuir-Blodgett films (poly(γ-methyl- d -glutamate-co-γ-n-alkyl- l -glutamate)) with their preferred molecular axis in the plane of the film. Surface acoustic modes, guided modes and bulk modes were obsersed. Samples with from 10 to 560 molecular monolayers were measured and the elastic constants were found to be of hexagonal symmetry and not to depend on the film thickness. The whole set of elastic constants of the Langmuir-Blodgett films was determined from the spectra: c11 = 4.74 GPa, c33 = 10.8 GPa, c12 = 3.43 GPa, c13 = 3.57 GPaandc44 = 0.91 GPa.

Elastic properties of CuCo multilayers

Abstract The acoustic phonon modes of sputter-deposited Cuue5f8Co multilayers were studied using Brillouin scattering. These are the first such measurements to be made on an f.c.c.-f.c.c. multilayer system. The multilayer samples had a fixed atomic percentage of cobalt (53 at.%). The effective elastic constants of the multilayer samples, which were obtained by comparing the data with calculated dispersion curves for the phonon modes, were independent of the multilayer modulation wavelength.

A new class of guided longitudinal acoustic phonons in ZnSe films on GaAs found by surface Brillouin scattering

Abstract A detailed investigation of a new class of long-wavelength acoustic film excitations, which we identify as longitudinal guided acoustic phonons, is presented. Despite a non-vanishing coupling to propagating transverse substrate modes, these new modes have lifetimes comparable to the Rayleigh mode and are the longitudinal counterpart to the well-known generalized Lamb or Sezawa modes of supported films. In ZnSe(001) films on GaAs(001) and in ZnS(001) films on Si(001) we were able to observe the longitudinal guided acoustic phonon by surface Brillouin spectroscopy. Calculations of the dispersion relations and of the scattering cross section using a general theory, taking all mechanical and electro-magnetic boundary conditions into account, show a good agreement with the experimental data.

Effect of thermal annealing on elastic properties of Ag/Pd superlattice films

Abstract We report a 50 % increase in the shear elastic constant c 55 in Ag/Pd superlattice films upon thermally annealing as measured by Brillouin light scattering. X-ray diffraction studies show that this increase is due to intermixing of the Ag and Pd layers.

Elastic properties of unpolymerized and polymerized cadmium octadecyl/fumarate and cadmium octadecyl/maleate Langmuir-Blodgett films determined by Brillouin scattering

We have measured the elastic properties of saturated ODF, and of unpolymerized and polymerized regular ODF, ODF/ODM, and ω‐ODF Langmuir–Blodgett films by means of Brillouin spectroscopy. Whereas the ODF/ODM films show a slight increase in the elastic constants, the regular ODF and ω‐ODF films exhibit elastic constants which are significantly softer in the polymerized films due to the formation of microcracks on polymerization.