Study of optical waveguide of barium sodium niobate films on potassium titanyl phosphate

Barium sodium niobate (BSN) optical waveguide films were grown on potassium titanyl phosphate (KTP) substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray pole spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the as-grown BSN films are epitaxially smooth, fine-particled and show small constituent deviation. Both m lines of the waveguided TE and TM modes were recorded. Lattice match between the BSN(110) and both the KTP(001) and KTP(100) planes is examined with mismatch less than 3%. Effective refractive indices as a function of incident wavelength and order of the waveguided modes are studied. A phase matching relationship of k ⁽¹⁾−2k ⁽⁰⁾=0 is established between the first-order and fundamental modes in the BSN/KTP waveguided system. Effective thicknesses for TE and TM modes were obtained to be equal to 0.76 and 0.72 μm, respectively, larger than the thickness of the as-grown BSN film of 0.60 μm. A constituent ratio of Ba:Na:Nb in the BSN film measured was equal to 2:0.82:5.14, slightly deviating from the stoichiometric ratio of 2:1:5, which is attributed to higher relative asymptotic velocity for Nb species and higher evaporation pressure for Na species. Finally, the main factors affecting quality of the as-grown BSN films are also discussed. Received: 26 March 1999 / Accepted: 30 March 1999 / Published online: 19 August 1999     

N‐Germyl derivatives of sulfacetamide and ortho‐(sulfonamido)phenylamines: characterization of N‐[o‐(N′,N′‐dimethylsulfonamido)phenyl]‐N‐dimesitylgermaimine

Triethylgermylation of sulfacetamide occurs on the sulfonamido nitrogen in competition with the 1,2 addition of the starting triethylgermyl dimethylamine on the carbonyl group. Thermal decomposition in the presence of dimethylamine yields N‐triethylgermylsulfanilamide. Stable 1:1 sulfacetamide–DBU and 1:1 sulfacetamide–Et₃N complexes were isolated and fully characterized in the course of dehydrochlorination reactions. o‐Sulfonamidophenylamine yields N,N′‐bis‐triethylgermylated derivatives, whereas o‐(N,N‐dimethylsulfonamido)phenylamine leads to monogermylated compounds. The N‐dimethylaminodimesitylgermyl derivative is thermally stable. Dehydrohalogenation of the N‐dimesitylfluorogermyl compound leads to the thermally stable but water sensitive N‐[o‐(N′,N′‐dimethylsulfonamido)phenyl]‐N‐dimesitylgermaimine. Copyright © 2003 John Wiley & Sons, Ltd.     

Shear viscosity of polymer and surfactant monolayers

The surface shear viscosity of monolayers formed at the surface of water by adsorbed polyethyl- eneoxyde and by stearic acid is measured as a function of the surface pressure of the monolayer using a new surface viscometer. The principle of the viscometer is the measurement of the drag force on a circular disk undergoing a uniform translation at the water surface: a hydrodynamic model based on the lubrication approximation allows a calculation of the surface viscosities from the absolute measurement of the drag forces. Received: 26 August 1999     

Structural and optical properties of Au-implanted ZnO films

The structural and luminescence related optical behaviours of Au ion implanted ZnO films grown by magnetic sputtering and their post implantation annealing behaviours in the temperature range of 100-700 °C have been investigated. Optical absorption and transmittance spectra of the films indicate that band edge of Au-implanted ZnO has shifted to high energy range and optical band gap has increased, because the sharp difference of thermal expansion induces the lattice mismatch between ZnO and SiO₂. PL spectra reveal that UV and visible luminescence bands of ZnO films can be improved after thermal annealing due to recovery of defects and Au ions incorporation. Importantly, green luminescence band of 530 nm has been only observed in the Au-implanted and subsequently annealed ZnO films and it enhances with the increasing annealing temperature, which can be related to Au atoms or clusters in ZnO films. Furthermore, X-ray photoelectron spectroscopy measurements reveal that the Au⁰ is dominant state in Au implanted and annealed ZnO films. Possible mechanisms, such as optical transitions of Au atoms or clusters and deep level luminescence of ZnO, have been proposed for green emission.     

Ultrafast spin dynamics in magnetic semiconductor quantum wells studied by magnetization modulation spectroscopy

1-x Mn_xTe quantum well structures at room temperature using time-resolved magnetization modulation spectroscopy. Access to the different electron and hole spin dynamics is obtained by carefully measuring the spectroscopic changes of the magneto-optical response during the first hundreds of femtoseconds after excitation. Experimental results are discussed in the framework of a simple model for a two-dimensional band structure. The spectroscopy is shown to be intimately related to the spectral band width of the applied ultrashort laser pulses. The general potential of the method for fundamental studies on other materials and systems is addressed. Received: 20 September 1998     

Time-resolved spectroscopy of soantaneous luminescence of CdSSe1−x quantum dots

Picosecond time-resolved spectroscopy of the edge luminescence band of CdS _x Se_1–x quantum dots with crystallite diameters as small as a few nanometers under band-to-band excitation reveals strong enhancement of the radiative recombination rate compared to bulk CdS owing to quantum confinement. The splitting of the luminescence band into two lines originates from near-band-gap absorption. Analysis of the temperature as well as the spectral dependence of the decay time (leading to a red shift of the luminescence with increasing time) and of the total-light-decay law result in a new model for the dominant radiative recombination channel: donor-acceptor pair recombination instead of an excitonic mechanism as claimed in previous publications.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Transmission second harmonic generation in CdTe at 1.064 μm

Transmission geometry measurements of the efficiency of second harmonic generation in various thicknesses of CdTe samples were made to determine the conversion efficiency dependence on material thickness. Neglecting pump depletion, it is found that for samples of well-defined symmetry, the second harmonic conversion efficiency scales with film thickness, with no observed enhancement owing to coherence length effects. The angular dependence of the observed second harmonic light in films of well-defined symmetry is consistent with second harmonic generation originating in the bulk.     

Analytical and numerical study on grating depth effects in grating coupled waveguide sensors

The in-coupling process for grating-coupled planar optical waveguide sensors is investigated in the case of TE waves. A simple analytical model based on the Rayleigh–Fourier–Kiselev method is applied to take into account the depth of the grating coupler, which is usually neglected in the modeling. Analytical expressions are derived both for the position and width of the in-coupling peaks to illustrate the effects of grating depth on the guided mode resonances in grating coupled waveguide sensors. Numerical computations verify the model for shallow gratings both in terms of peak shape and position and provide the limitations for the analytical formulas.     

Optical properties of Zn0.5Cd0.5Se thin films grown on InP by molecular beam epitaxy

We report photoluminescence (PL) and reflectivity measurements of Zn_0.5Cd_0.5Se epilayers grown by molecular beam epitaxy on InP substrates. The low-temperature PL spectra are dominated by asymmetric lines, which can be deconvoluted into two Gaussian peaks with a separation of ∼8 meV. The behavior of these peaks is studied as a function of excitation intensity and temperature, revealing that these are free exciton (FE) and bound exciton emission lines. Two lower energy emission lines are also observed and assigned to the first and second longitudinal optical phonon replicas of the FE emission. The temperature dependence of the intensity, line width, and energy of the dominant emission lines are described by an Arrhenius plot, a Bose-Einstein type relationship, Varshni's and Bose-Einstein equations, respectively.     

Simulation of the Propagation Property of Metal Wires Terahertz Waveguides

The propagation property of metal wires terahertz waveguides is studied and simulated under the framework of the Sommerfeld model. The group velocity dispersion, attenuation amplitude, transverse magnetic mode and propagating energy have been obtained by numerically solving the complex eigenvalue equation for the propagation constant. It is found that the group velocity dispersion and attenuation amplitude decrease with the increasing radii of metal wires. The energy power within the dielectric layer increase with the increase of radiation frequency.