The beam propagation properties of the high-powered Multi-Quantum-Well (MQW) laser diode (LD) are definitive elements in many application fields such as micro-processing, biomedical technique, and basic research, etc. In this study, the beam characteristics of a high-powered InGaAs/AlGaAs MQW-LD have been evaluated in both fast-axis and slow-axis. The multi-planar waveguide model and the non-paraxial second-order moment theory were used in analyses of the beam propagation features in the direction perpendicular to the active layer of a MQW-LD. The experimental results of the beam character measurement accord with those of the theoretical calculation very well for a sampled InGaAs/AlGaAs MQW-LD. The analysis approach is thought to be useful for design of the LDs and the other waveguiding optical devices.
Nickel oxide films were deposited onto indium-tin oxide coated substrates by electron-beam evaporation and were electrochemically colored and bleached in KOH electrolyte. X-ray diffraction, infrared, x-ray photoelectronic and Raman spectroscopy were used to characterize the films. Results show that the as-deposited films are composed of crystallites with preferential orientation of cubic NiO(111), and retain their original structure after electrochromic redox reaction. The boundary and surface of the NiO crystallites play a critical role in the electrochromic reaction, the sites of the injection and ejection of OH<SUP>-</SUP> ions and relevant electrochromic reaction are at the interface of NiO crystallites, the major composition at the interfaces of the crystallites are NiO for the as-deposited films, NiOOH for the colored films and Ni(OH)<SUB>2</SUB> for the bleached films.
Vanadium pentoxide films were prepared by evaporation followed by annealing post-treatment in O<SUB>2</SUB> atmosphere. Lithium was inserted electrochemically from an electrolyde into vanadium pentoxide films so that Li<SUB>x</SUB>V<SUB>2</SUB>O<SUB>5</SUB> was formed. The structure of the post-treated samples was determined by XRD and infrared reflectance was measured by FTIR for as-grown and lithiated films, respectively. The experimental results have shown that V<SUB>2</SUB>O<SUB>5</SUB> thin films have some infrared absorption peaks located at 982, 824, 527 and 504 cm<SUP>-1</SUP>, and the infrared vibration bands corresponding to the peaks have a good agreement with the analysis by Abello et al. for polycrystalline V<SUB>2</SUB>O<SUB>5</SUB>, and there is an obvious influence of lithium insertion on the infrared vibration properties which may be reconciled with the lattice change such as expansion and contraction.
Based on the hydrodynamical model, we develop a transfer matrix formalism to study the optical properties of a superlattice which is composed of two alternating conducting slabs and is subjected to an external static magnetic field parallel to the interfaces. The retardation and collisional damping effects are taken into account. We present the dispersion relations of the electromagnetic modes for an infinite periodic structure and calculate the reflection spectra for a finite system. The localization of the polaritons in a quasi-periodic multilayers is discussed by plotting the amplitudes of the electric field. We find that the dispersion relations are obviously modified by the external magnetic field, and the reflection spectra show rich structure when the magnetic field is applied. The spectra of the electromagnetic modes for the quasi-periodic multilayers exhibit a Cantor-like structure with a scaling property. A transition of extended states to localized states is possible when we vary the applied magnetic field.
The optical properties of a cantor-like metal-insulator superlattice for both p-polarized and s- polarized wave are studied by employing the transfer matrix formalism. Based on the hydrodynamic theory and taking account of retardation effect, we have calculated the dispersion relations of the electromagnetic modes of the superlattices. The results show that the dispersion relations of the modes have rich multi-fractal structure, and the frequency gaps, in which there are strong reflective peaks, appear strikingly in the region of the extreme ultraviolet and soft x-ray. Around the fixed points, the patterns of the bands are scale invariant.
A quasi-periodic design method for soft x-ray multilayer reflector to achieve high reflectivity and low loss is presented. The dependence of the reflectivity on the optical constants of the absorbing layers for a given substrate and spacer materials is investigated, and the criterion of choosing optical components is also discussed. We find that when the extinction coefficient of the absorber is large, the reflectivity of the multilayer reflector is governed by the difference of the extinction coefficients of the components. In order to obtain high reflectivity in the case of large extinction coefficient, one should choose a pair of materials with large difference of extinction coefficients.
The scaling properties of the optical reflectance from two types of quasi-periodic metal- insulator superlattices, one with the structure of Cantor bars and the other with the structure of Cantorian-Fibonaccian train, have been studied for the region of s-polarized soft x-rays and extreme ultraviolet. By using the hydrodynamic model of electron dynamics and transfer- matrix method, and by taking into account retardation effects, we have presented the formalism of the reflectivity for the superlattices. From our numerical results, we found that the reflection spectra of the quasi-superlattices have a rich structure of self-similarity. The interesting scaling indices of the spectra, which are related to the fractal dimensions, are also discussed for the two kinds of the quasi-superlattices.