Liliana Preda

Structural characteristics of RF-sputtered BaTiO3 thin films

Abstract In this work some structural characteristics of the thin films deposited by a radio frequency-magnetron sputtering technique from a hot pressed BaTiO3 ceramic target were studied. The Ba/Ti ratio was measured by means of X-ray fluorescence in order to determine the real chemical composition of the films. The results showed that this ratio varied along the radial axis of the discharge. Besides, the evolution in phase composition of the annealed films as a function of the thermal treatment conditions (temperature and plateau) as well as the structural characteristics (unit cell parameter and crystallite size) were investigated by X-ray diffraction (XRD). Infrared (IR) and Raman spectroscopies were used in order to obtain more details about the distorted structure of such fine-grained thin films. In the case of these films, Raman spectroscopy carried out from 99 to 473 K did not emphasize steep, distinct transitions between the different polycrystalline BaTiO3 forms when compared with the bulk BaTiO3.

Independent and combined information transfer from axicon and helical phase distributions.

Helical phase distributions used for optical information transfer increase its capacity by offering a characteristic spatial intensity arrangement for the diffracted beam. Here we propose the superposition between helical phase distribution with an axicon type. They form a composed object placed in the object arm to generate holographic masks. The diffracted patterns from these masks exhibit asymmetric shapes and peaks along the optical axis, with two kinds of spots, which contain independent or combined information from both phase distribution constructive parameters. To read these parameters based only on the diffraction patterns analysis, we generate the match reading masks (RMs) to be inserted in the optical path. In this proof-of-concept experiment, we demonstrate that one can sort constructive parameter values of each phase distribution, from both kinds of spots, using specific RMs.

A Generalized Devil Staircase-Based Generator for the JPY-USD Exchange Rate?

Abstract By exploiting the linear similarity between two series, namely the exchange rate Japanese Yen - United States Dollar (JPY-USD), and the generalized devil staircase (GDS) recursive plot, the possibility of synthesizing the real series by using the GDS generator is investigated. The properties of the real and simulated series are compared from both fractal and chaotic perspective using a new multifractal deviation factor, and a crossing analysis based on correlation dimension and non linear prediction error, respectively. Given the encouraging results supported by good fitting values, there are arguments to consider the method an alternative for time series modeling on deterministic assumptions.

Diffraction patterns from holographic masks generated using combined axicon and helical phase distributions

The diffraction patterns (DPs) from helical phase distributions were intensively studied due to their peculiar capability of carrying orbital angular momentum. In the present study, we investigated the combination between a helical phase distribution and another distribution: axicon in our case. Such phase distributions were digitally embedded into holographic masks (HMs). The reconstruction step is performed by simulating the propagation through these HMs, using scalar diffraction theory, Fraunhofer approximation. The spatial intensity arrangement of the DPs is investigated linked with the radial and azimuthal constructive parameters values of the diffractive phase structures embedded in the HMs and transferred in these DPs. Keywords: helical phase distribution

Optical information transfer based on helico-conical laser beams

We generated holographic masks starting with the interference between the reference beam and the signal beam, which is diffracted by the object. We investigate additive and multiplicative combinations between conical and helical phase distributions as compound objects to be inserted in the signal beam. We explored experimentally the dynamics of the diffracted intensity patterns, in two and three dimensions, after these holographic masks are addressed onto a programmable spatial light modulator. The diffracted intensity spatial arrangement contain information about constructive parameters used for holographic masks generation and exhibit asymmetric shapes and peaks along the optical axis in all analyzed compound objects. We introduce a reading mask in the optical path and, by analyzing changes of the spatial distribution in the final diffracted intensity arrangement, is possible to read the values of the constructive parameters. The generation of these reading masks in each case is discussed.

Light control using photonic crystals and metallic slits

A numerical analysis of TE mode of electric field propagation through the interface between a thin film of TiO2 and periodic metal slits of silver is presented. The lossy metallic slits are optically described by Drude model. A grid of regular slits generates sharp hotspots of electric field at the exit plane. Adding a 2D rectangular photonic crystal made of air cylinders in titanium dioxide will enhance the electric field at the exit from the metallic slits without any loses in propagation distance and peak width. An optimization of geometrical parameters of metallic slits and photonic crystals is made for the propagation of a visible incident radiation with the wavelength of 650nm.

Quasi-periodic structure analysis by digital holography

We analyze an optical system consisting of a number of basically elements (BE) arranged in a quasi-periodic structure (QPS) of phyllotaxis type, which offers the best packing in many natural bodies. In our simulations, we change the parameters which generate this QPS to find its diffractive optical properties. This structure is then made on glass using e-beam lithography. To characterize this QPS, we use the digital holography (DH) method to reconstruct the amplitude and also the phase in object plane (QPS plane). Using different parameters of the spherical reference wave for holograms recording we change the contrast in holograms to improve the reconstruction of the object.

Iterative algorithm analysis for phase-only diffractive control access system

A new architecture with two phases-only diffractive elements and one decryption mask for optical control access system is presented. Only three different persons which keep this element have the permission to access together. The Iterative Fourier Transform Algorithm (IFTA) is analyzed for phase-only diffractive optical elements (PODE) design with different constraints in the input and output plane and the optimal variant is chosen for better image quality in the output plane (big value for diffraction efficiency and small value for merit function and signal to noise ratio). For higher security we propose different incident waves. That are compared with the case when the first phase-only diffractive element and decryption masks are designed together in an extended iteration and the output images of them (first desired image) is taken over the second phase-only diffractive element. In order to increase security level, this finally PODE are designed to increase some parts from the first desired image. Only with this condition the key image on the detector is formed.

Magneto-mechanical oscillations revisited

Here we study the temporal evolution of a magnetemechanical, inverted spherical pendulum. The oscillator is a rigid, stainless steel, hollow needle. The needle has one end fixed in a spherical-like articulation, while the other extremity has no mechanical contact. The oscillation is driven by a longitudinal, periodically magnetic field added to a constant value of a static field. A video camera takes simultaneously the optical images of the projections of the oscillating needle along two mutually normal directions. The pairs of temporal sequences are analyzed in the real space, phase space and Fourier space. Among all the external parameter that can be usually varied, like the strength of the static magnetic field, the amplitude and the frequency of the driving magnetic field, or the momentum of inertia of the oscillating body, of a crucial importance seems to be the magnetc-mechanical feed-back of the oscillating system.

The influence of the rise time of the excitation pulse upon the output of a copper bromide laser

Considering the rise time (understanding the rise speed as well) of the electrical intensity of the pumping pulse as the key parameter characterizing the output power of a copper-type laser, we present here a simplified model of the main kinetic processes occuring during the electrical pumping pulse and afterglow in a Ne-CuBr laser. The a priori knowledge of the typical temporal behavior of the electron density and electron temperature reduces the number of coupled differential equation to be solved. The importance of the parasitic radiative filling of the lower laser levels 2D via channels that are not involving the upper laser levels 2P is enhanced. The comparative green-yellow lasing efficiencies and the temporal timing of the optical pulses with respect to the excitation pulse are consistent with the experiments.