Fringe Structure Research Articles

Digital Photography in Measurements of Shifts of Object Surfaces with Formation of the Speckle Structure In White Light

We describe and analyze the experimental realization of a speckle interferometry scheme designed for measurement of the value of the shift of the object surface along the surface itself. In contrast to classical speckle interferometric schemes, we use a specially formed two-dimensional pattern of the random binary structure as a speckle structure. The pattern being illuminated by the white light is photographed with the use of a digital camera. Further processing of the information related to the Fourier transformation of the pictures registered and determination of the obtained fringe structure period is carried out in a PC.

Devitrification of Al-based glass forming alloys

Abstract Al 88 Y 7 Fe 5 samples were rapidly quenched into a fully amorphous state. Calorimetric investigations together with X-ray diffraction analyses show that a primary crystallization of Al-nanocrystals occurs at the onset temperature of 276 °C. Isothermal annealing treatments that were performed for different times at temperatures well below the primary crystallization onset observed during rate heating show that Al-nanocrystals develop after short periods. Moreover, these investigations indicate the formation of a transient phase that formed at higher temperatures only after annealing at lower temperatures for intermediate time intervals. Additionally, HRTEM analyses show a fringe structure in the matrix surrounding the nanocrystals that corresponds to the transient phase crystallites. The results are discussed in the context of nucleation in the presence of concentration gradients at the nanocrystal/glass interface.

A Neutron Reflectivity Study of Drainage and Stratification of AOT Foam Films

Structural properties of Aerosol-OT (AOT) foam films were studied by neutron reflectometry. The drainage of large (10 cm2), horizontally oriented AOT films under zero applied external pressure is slow and proceeds from thick colored or gray films to black films of approximately 200 Å thickness over many hours, resulting in quasi-static conditions over the time scales required for the acquisition of reflectivity profiles throughout the whole drainage process. After formation of the foam filmwhile still showing colored interference fringesand during the early stages of thinning, the appearance of Bragg diffraction peaks demonstrates that the film contains multilamellar structure, in agreement with studies at free air/water interfaces. Upon further reduction of the film thickness, below approximately 250 Å, the reflectivity profile is well fitted by a three-layer slab model with two surfactant layers and an aqueous core with a high surfactant content. The composition of the aqueous core and the manner in which the reflectivity during the latter stages of draining evolves from Bragg peaks to a Kiessig fringe structure indicate stratification within the thin foam film.

Fabrication and analysis of a three-layer stratified volume diffractive optical element high-efficiency grating

We have demonstrated a high-efficiency grating (>80%) using a three-layer Stratified Volume Diffractive Optical Element (SVDOE). Its angular sensitivity was measured optically and shown to agree extremely well with simulations performed using rigorous coupled wave analysis (RCWA). Further simulations predict an increase in efficiency as the number of layers is increased. An SVDOE consists of binary grating layers interleaved with homogeneous layers. The binary grating layers are shifted laterally relative to each other to emulate a volume holographic grating with slanted fringes. Creating the slanted fringe structure permits the preferred incidence angle of the SVDOE to be rotated to any arbitrary position. Achieving the relative offset between grating layers is the most challenging fabrication step and required the development of a high-precision alignment technique that was implemented on a contact mask aligner. The approach is based on monitoring the diffraction signal of a beam that is transmitted through gratings on the substrate and those on the mask as they are translated with respect to one another during pre-exposure alignment. The homogeneous layers are fabricated using a polymer material, SU-8, that is spin-coated and then planarized during its curing process.

Transmission characteristics of Sagnac interferometers based on fiber Bragg gratings

We present a comprehensive study of the transmission characteristics of all-fiber Sagnac interferometers (FSIs) based on fiber Bragg gratings (FBGs). Analytic and numerical models have been developed for the design and characterization of FBG FSIs that incorporate gratings of arbitrary fringe structure. The transmission, phase, and time delay responses of several representative configurations that incorporate uniform-period and chirped gratings with and without apodization have been investigated theoretically and experimentally. Excellent agreement between the theoretical results and real device characteristics has been found in all cases. Our study clearly reveals that fiber grating-based FSIs offer potentially significant practical advantages not only for conversion of the reflective response of the grating into a transmissive response without loss but also by providing near-zero dispersion in the transmission bands, which offers attractive prospects for filtering components in high-speed wavelength-division multiplexing transmission systems.

Quantum fluctuations in one-dimensional arrays of condensates

The effects of quantum and thermal fluctuations upon the fringe structure predicted to be observable in the momentum distribution of coupled Bose-Einstein condensates are studied by the effective-potential method. For a double-well trap, the coherence factor recently introduced by Pitaevskii and Stringari [Phys. Rev. Lett. 87, 180402 (2001)] is calculated using the effective potential approach and is found in good agreement with their result. The calculations are extended to the case of a one-dimensional array of condensates, showing that quantum effects are essentially described through a simple renormalization of the energy scale in the classical analytical expression for the fringe structure. The consequences for the experimental observability are discussed.

Fringe structure in the phase-space dynamics of atomic stabilization in an intense field

An analytical expression of a Floquet operator, which describes the evolution of a wave packet in combined atomic and an intense laser field, is obtained approximately in the stabilization regime. Both the classical and quantum versions of the Floquet operator are used to study the phase-space dynamics of atomic stabilization, and the fringe in the phase-space is clearly demonstrated. Furthermore, we investigate the dynamical mechanism and characters of this striking structure, and find that this structure is very closely related to the classical invariant manifolds.

Structure and Switching in Bent-Shaped Molecular Liquid Crystal Systems with Two Mesogenic Groups Linked by Alkylene Spacer

Structure and switching behavior were studied in liquid crystals consisting of bent-shaped molecules with the linkage of an alkylene spacer, m(O)AMnAM(O)m, where m and n are carbon numbers of end and spacer chains, respectively. All the compounds exhibit a fan-shaped texture without a fringe structure in their smectic phase, different from the texture of conventional bent (banana)-shaped liquid crystals. In 12AM5AM12, two switching current peaks indicating the antiferroelectric phase were observed. The spontaneous polarization was about 600 nC/cm2. The color change due to the birefringence change is associated with the switching, though the extinction direction between crossed polarizers remains the same. This clearly proves that the bent-molecules do not tilt with respect to the layer normal. In the dielectric measurements, there exist two relaxations at 600 kHz and below 100 Hz and they are suppressed by a biased voltage. Structure and switching in the other systems, 80AM5AMO8, are also described briefly.

Production of CO2 in the capillary fringe of a deep phreatic aquifer

CO2 profiles obtained along a 30‐m‐thick unsaturated zone under land irrigated with sewage effluents show two production regions: a seasonal one in the root zone and another, at steady state, near the water table (29 m). On an annual basis the CO2 flux from the deep source toward the atmosphere (6.3 g C m−2 yr−1) is balanced by a similar influx of soluble organic carbon (SOC) from sewage effluents. The δ13C values of soil CO2 indicate that CO2 is produced from plant material in the root zone and from biodegradation of total sedimentary organic carbon in the capillary fringe. High CO2 concentration in the capillary fringe (up to 2%) is likely to reflect a decrease in diffusivity relative to the unsaturated zone due to increase in both water content and tortuosity induced by the capillary fringe structure. The long residence time of SOC and CO2 in the unsaturated zone (29 years at the study site) suggests that the unsaturated zone of deep aquifers may have a significant storage capacity for carbon and may act as a temporary carbon sink.

Fringe effect on critical current of a gold film percolation system

In this paper, the fringe effect on critical current has been studied systematically by measuring the electric transport characteristics of a Au-film system with diffuse fringe structure. It is found experimentally that, when the fringe effect becomes obvious, the film will exhibit strange I-R characteristics, in which exist a balance current and a critical current. We find that the critical exponents are related to the diffuse fringe structure of the films. The detailed analysis shows that the characteristics result from the thermionic-activating conductive effect in the diffuse fringe film system.

Critical behavior of a metallic diffuse-fringe film percolation system

Preparation of a metallic diffuse-fringe film system and its electrical properties are reported. The anomalousR-I characteristics, third-harmonic coefficient and critical behavior are observed in the film system. Analysis shows that this behavior is caused by the location-dependent tunneling and hopping effects, which result from. the continuous variation of the diffuse fringe structure of the film due to the increase of the current.

Conductivity measurements of a metallic diffuse-fringe film percolation system

We have fabricated a metallic diffuse-fringe film system by dc-magnetron spulleririg method. The diffuse fringe structure of the film system is obviously observed when during the film deposition process the distance between the shutter slit and the substrate is large enough. An anomalous, nonlinear I-V behavior is found in the system and can be well explained by the Joule heating and hopping effects. The strong dependence between the conductivity behavior and the fringe indicates that the fringe effect is very severe in this inhomogeneous percolation system.

Electrical transport behavior of an Au diffuse fringe film percolation system

The preparation of a metallic diffuse fringe film system by dc-magnetron sputtering is described. The diffuse fringe structure of the film system is clearly observed in the SEM photograph when, during the film deposition process, the distance between the slit shutter and the substrate is large enough. Our experimental results show that the anomalous nonlinear I-V behavior of the system is mainly caused by the diffuse fringe effect. The temperature dependence of the sheet resistance is similar to that of the metallic flat film system in the temperature interval 77-300 K.

Possibilities of near backward light scattering for characterizing dense particle systems

A backscattering probe has been tested as an alternative to the more common forward light scattering technique for particle size determination. The backscattering signature of an ensemble of spherical particles in front of the probe window was measured with a charged coupled device (CCD) camera and compared with Lorenz-Mie calculations. The fringe structure allows the measurement of particle size. However, the width of the size distribution must be small to observed the fringes. The phenomenon of enhanced backscattering in concentrated random particle media is investigated and discussed. The width of the coherent backscatter peak, due to multiple scattering serves as an indicator for the mean particle size, independent of the shape of the particles. The total amount of backscattered light is an indication of the total reflecting surface area of the sample.

X-Ray Interference Measurements of Ultrathin Semiconductor Layers

AbstractWe present various x-ray diffraction phenomena from semiconductor hetero-epitaxial layers. Each of these phenomena gives useful information on the layers. Knowing what to look for in the x-ray rocking curve (XRC) can make this nondestructive technique a very powerful tool for characterization of a few A-several g.tm thick layers We discuss the use of individual Bragg peak, diffraction fringe, and interference structure to obtain layer information. We particularly emphasize the use of x-ray interference in studying buried strained quantum well or quantum barrier layers. We present experimental rocking curves of an AlGaAs/GaAs double heterojunction laser structure and GaInAs/GaAs strained layer superlattices in both <001> and <111> orientations.

Studies on the structure and the crystallization process of ion sputtered TiSe 2 films

Structures of argon ion sputter-deposited TiSe 2 films have been studied by electron microscopy. The as-deposited films showed typical diffraction haloes. The measured density of the film showed that the as-deposited film has a composition corresponding to TiSe 2. High resolution electron microscopy images showed crossed fringe structure of the order of 1 nm in size. Therefore, it may be concluded that the as-deposited film was composed of TiSe 2 micro-crystallites. By irradiation of the as-deposited film with an electron beam of the order of 100 A/cm 2, the film crystallized to TiSe 2 crystallites of a few nm in size. By further irradiation with an intense electron beam, they showed a change and growth to a grain size of a few tens of nm of Ti 5Se 8. These Ti 5Se 8 films gradually changed to the TiSe 1.5 crystals.

NDT by speckle rotational shear interferometry

Speckle rotational shear interferometry has been used for NDT of diffuse objects. Shear is obtained by placing a pair of Dove prisms before a double aperture arrangement. For centrosymmetric objects, defects appear in a fringe-free field when shear is introduced about the centre, unlike other shear techniques where defects appear in a parent fringe structure. Furthermore, by eccentric loading and rotational shear applied about the centre, sensitivity for defect detection can be enhanced. A qualitative theory and experimental results are presented.

Computer-generated holograms for geometric transformations

Theory and experiments in the area of computer-generated holograms for geometric transformations are presented. Geometric transform holograms are divided into two categories: (1) those which have a continuous fringe structure, and (2) those which consist of a set of discrete subholograms. Criteria for the realizability of a continuous geometric transform hologram are described. Examples of both types of hologram are to map rings of different radii to a linear sequence of points. They allow the replacement of a ring developed detector by a linear detector array without loss of signal energy and can be applied to optical spectrum analysis and angle-wavelength multiplexing for data transmission through optical fibers.

Optical effects resulting from deep implants of silicon with nitrogen and phosphorus

Abstract Single crystal silicon has been implanted with nitrogen and phosphorus ions at MeV energies to fluences between 1016 and 1.6 × 1018 ions/cm2. Infrared transmission and reflection spectra in the range of 1.25 to 40 μm were measured for as-implanted samples and after various annealing treatments. Interference fringes were observed in the IR spectra which are produced by the interference of light which has been multiply reflected between the front surface and the buried layers. By detailed theoretical analyses of the interference fringe structure, we obtained refractive index profiles, which, under suitable interpretation, provide accurate measurements and several quantities of interest. These quantities are the range and straggling of the implanted ions, the depth of disordered layers, and the width of the order-disorder transition. Mechanisms for the refractive index changes which have been identified include amorphization of the implanted silicon, bulk compositional change in the buried layer, localized vibrational mode dispersion, and free electron dispersion. Experimental results and theoretical predictions are presented, demonstrating each of these mechanisms.

An explanation of the Lau effect based on coherence theory

The Lau effect is investigated as a result of the propagation of partially coherent light. It is found that the fringe structure is dependent on the relationship between the grating separation and the periodicity of the complex degree of spatial coherence in the plane of the second grating. This provides a simple and elegant means of interpreting and extending the Lau effect.