Changes In Intensity Patterns Research Articles

Orbital Angular Momentum (OAM) Mode Mixing in a Bent Step Index Fiber in Perturbation Theory: Multiple Bends

In this article, we address the impact of multiple fiber bends on orbital angular momentum (OAM) mode propagation in a fiber. In particular, we extend the OAM mode-mixing due to a single-fiber bend studied earlier in detail for the step-index fiber, to the case of a succession of bends. The bends may have a relative orientation with respect to each other. Analytic expressions leading to crosstalk are given. The OAM mode intensity at the output of a pair of bends is especially studied with emphasis on the intensity pattern changes that arise from the changes in the relative orientation of the bends.

Focusing properties of radially polarized Bessel-like beam with radial cosine phase wavefront by a high numerical aperture objective

By the use of the vector diffraction theory, the focusing properties of radially polarized Bessel-like beam with radial cosine wave front phase through a high numerical-aperture (NA) lens are investigated theoretically and numerically in this work. The wave front phase distribution is a cosine function of radial coordinate. Calculation results show that focus shift is considerably influenced by changing frequency parameter C and topological charge. An increase on the focus shift C, the total intensity pattern changes remarkably and it focuses along the optical propagation axis. Thus, the focal shift direction can be adjusted by the change of the frequency parameter in cosine function. In this paper, the generation of the focal spot allows an increase in focal length in the axial direction of the incident beam propagation. Under higher numerical aperture (NA = 0.95), the effect of the frequency parameter and topological charge on the focal pattern gets stronger.

Compatibility study of alginate/keratin blend for biopolymer development.

The ultimate characteristics of blend film depend on the properties of its polymeric components, composition, and on the compatibility of the polymers. Binary polymer blend films of alginate (ALG) and keratin (KER) fibers (obtained from chicken feathers) were prepared by simple solution casting techniques and their compatibility properties were studied by X-ray diffraction and scanning electron microscopy. The tensile strength and percent of elongation were measured by a tensile strength tester. The results of the present studies elucidate that ALG and KER are compatible and suitable for the development of a blend film. It was found that the ALG/KER blend ratios of 90:10 and 80:20 possess characteristics to make a blend film with a high tensile strength value. The blend with composition 90:10 of ALG/KER is the one of the strongest candidates in the preparation of blending films, because it has the highest tensile strength (0.38 MPa) and percentage of elongation (59.5%) among all tested blend compositions. The blend ratio of 80:20 of ALG/KER achieves maximum compatibility, since its intensity pattern changes drastically as recorded in an X-ray diffraction study. The fabricated blend film can be a suitable candidate for a range of biomaterials such as for a drug delivery vesicle, hydrogel, and scaffolding, etc.

Unidirectional growth and characterization of mixed crystals: Na(I)-incorporated KDP

The effect of dopant alkali metal Na(I) (over a wide concentration range from 0.33 to 0.75mol%) on the growth process, external morphology, vibration patterns, XRD profile, thermal studies, optical density and second order nonlinear optical (NLO) properties of potassium dihydrogen phosphate (KDP) crystals grown by the slow evaporation solution growth (SEST) and Sankaranarayanan–Ramasamy (SR) techniques has been systematically investigated. Incorporation of the dopant into the crystalline matrix even at a low concentration was well confirmed by energy dispersive X-ray spectra (EDS). The change in intensity patterns in XRD profiles of doping specimens reveals lattice distortion, further supported by slight shifts in characteristic vibrational frequencies in FT-IR. UV–vis study shows that the transparency is not affected much by the dopants and the diffuse reflectance data were employed to estimate the band gap energy by the application of Kubelka–Munk algorithm. The thermogravimetric/differential thermal analysis reveals the purity of the sample and no decomposition is observed upto the melting point. The surface morphology of the as-grown specimens changes with concentration of dopant. The second harmonic generation (SHG) efficiency is enhanced considerably when the concentration of the dopant is equal to that of host material in the mixed crystal while depressed activity is observed when the concentration of one of the compounds is high.

Generation of radially polarized Bessel–Gaussian beams from c-cut Nd:YVO_4 laser

We experimentally demonstrate the generation of radially polarized Bessel-Gaussian beams from a c-cut Nd:YVO₄ laser with a hemispherical cavity configuration by proper mode control. The output beam has an annular-shaped intensity distribution with radial polarization. When the beam is focused, the intensity pattern changes to a multi-ring, which is a typical characteristic of the lowest transverse mode of vector Bessel-Gaussian beam. Higher-order modes of vector Bessel-Gaussian beam are also observed from the same cavity by slightly changing the cavity alignment. The experimental results show a good agreement with the simulation results for both focal and far fields. The present method is a simple and direct way for generating vector Bessel-Gaussian beams.

Influence of Cs(I)-doping on the spectral, thermal, morphological and optical properties of bis(thiourea)zinc(II) chloride crystals

Single crystals of alkali metal caesium(I) doped bis(thiourea)zinc(II) chloride are grown at room temperature by slow evaporation solution growth technique. Powder XRD studies reveal some interesting features in the XRD profiles with changes in intensity patterns in doped specimen due to stress development in the crystal. The incorporation of Cs(I) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy. Slight shifts in vibrational patterns of doped specimen indicate that the crystal undergoes considerable lattice stress as result of doping. SEM studies of pure and doped samples reveal the external morphology. Thermogravimetric and differential thermal studies reveal the purity of the material and the specimens are stable up to the melting point. The optical studies reveal that absorption is minimum in the visible region and doping influenced the diffuse reflectance spectrum. The band gap energies of the pure and doped specimens were estimated by the application of Kubelka–Munk algorithm.

Synthesis, growth, characterization and crystal structure of zinc cadmium thiourea complex Zn0.625Cd1.375(CS(NH2)2)9.4(SO4)

Single crystals of zinc cadmium thiourea complex Zn0.625Cd1.375(CS(NH2)2)9.4(SO4) (ZCTS) are grown by slow evaporation of aqueous solution containing zinc sulfate, cadmium sulfate and thiourea in the ratio 1:1:6. Crystal composition as determined by single crystal X-ray diffraction analysis reveals that it belongs to the monoclinic system with space group P21 and cell parameters are a=13.263(5)Å, b=11.886(5)Å, c=27.215(5)Å, α=γ=90.000(5)°, β=96.586(5)°, V=4262(3)Å3 and Z=2. The presence of zinc and cadmium in the final product is further confirmed by inductively coupled plasma (ICP), atomic absorption spectroscopy (AAS) and energy dispersive X-ray spectroscopy (EDS). The vibrational patterns in FT-IR are used for identifying the material and the thermal analysis by TG/DTA indicates the stability of the mixed crystal. The surface morphology changes of the mixed crystal are studied by scanning electron microscopy (SEM). High transmittance in the visible region is observed with a lower optical cut-off at ∼260nm. The change in intensity patterns in XRD profiles indicates lattice distortion. The relative second harmonic generation (SHG) efficiency measurements reveal that the mixed crystal has a superior activity than that of tris(thiourea)zinc(II) sulfate (ZTS).

Traffic Sign Recognition Utilizing an Eigen Space Method Based on the KL Transform

This study explains that a method utilizing the eigen spaces obtained by the KL transform for automatic recognition by camera of the speed on a speed limit sign has the following advantages: it is robust in response to changes in intensity patterns caused by the direction the sign is facing and by the amount of light striking the sign, and it is able to reduce the recognition processing time by reducing the number of feature vector dimensions during analysis. The method for recognition of traffic signs previously proposed by the authors of this study was a method for recognition based on extracting geometric shapes from the sign and recognizing them based on their aspect ratios. As such, this method was not able to identify the numbers on a speed limit sign, all of which have identical aspect ratios. It will be shown that the method in this study is able to recognize nearly all speed limits indicated on traffic signs within several 100s of ms after image acquisition. This method was applied to still images and its effectiveness was verified from the perspective of the following requirements for providing accurate information concerning the vehicle surroundings to the driver: high processing speed, high recognition accuracy, detection of all detectable objects without omission, and robustness in response to changes in the surrounding environment.

The concentration effects of s-, p-, d- and f-block element doping on the growth, crystalline perfection and properties of KDP crystals

The effect of dopants (over a wide concentration range from 0.5 to 10 mol%), namely s-, p-, d- and f-block elements (Mg, Sb, Pd and La) on the growth process, crystalline perfection, external morphology, vibrational patterns, XRD profile and second order nonlinear optical (NLO) properties of potassium dihydrogen phosphate (KH2PO4, KDP) crystals grown by the slow evaporation solution growth technique has been systematically investigated. Incorporation of the dopants into the crystalline matrix even at low concentrations was well confirmed by the inductively coupled plasma (ICP) technique. The change in intensity patterns in XRD profiles of doping specimens reveals lattice distortion, further supported by slight shifts in characteristic vibrational frequencies in FT-IR. The scanning electron microscope (SEM) micrographs exhibit the effectiveness of the impurity in varying the surface morphology. The high-resolution X-ray diffraction (HRXRD) studies used to evaluate the crystalline perfection reveal many interesting features on the ability of accommodating the dopants by the crystalline matrix. It appears that the crystalline perfection depends mostly on the concentration of the dopant. Multi-peaks appear for highly doped specimens indicating the inhomogeneous accommodation. The second harmonic generation (SHG) efficiency is enhanced considerably when the concentration of the dopant is low while depressed activity is observed with poor crystalline perfection at high concentrations irrespective of the nature of the dopants.

Transmission Electron Microscopy and Luminescence Studies of Quantum Well Structures Resulting from Stacking Fault Formation in 4H-SiC Layers

The formation of 3C-SiC staking fault inclusions in higher band-gap other SiC polytypes provides a unique possibility to obtain quantum well (QW) structures without changing of chemical composition of epitaxial layers during growth. [1] In this report we present low temperature microphotoluminescence and transmission electron microscopy (TEM) studies of 3C-SiC stacking faults inclusions in 4H-SiC homoepitaxial layers, grown by molecular vapor deposition (MOCVD) on 4H-SiC substrates with an 8o surface miscut from the basal plane. TEM investigations showed that basal plane inclusion with cubic 3CSiC stacking faults present in the substrate propagate into the 4H-SiC layer material, forming inclined QW structures. The distance between SF was found to vary from 2 nm to 1.5 μm depending on the position on the layer. The presence of SF in the layer was confirmed by photoluminescence studies. They showed that in addition to excitonic emission typical for high quality 4H-SiC layers, well defined group of several emission lines around energy of 2.9 eV, which we attribute to QW formation induced by 3C-SiC staking faults [2]. In contrary to the emission due to nitrogen-bound excitons (observed at higher energy), which remains practically unchanged when changing position on the sample, the energy of spectral lines related to SF emission shows quasi-periodic jumps between well defined values when scanning on the sample surface (laser spot on the sample is of about 1-2 μm). The observed intensity pattern changes in a similar way. The obtained experimental data are discussed in terms of single, double and multiple quantum wells formed form neighboring 3C-SiC SF layers. It is confirmed that a concept of “structure-only” QW is promising from the point of view applications, provided precise control of FS formation during the growth of SiC based nanostructures is attainable. Our results show that, at least the formation of SF related QW structures can be successfully initiated by appropriate substrate preparation.

Influence of inorganic and organic additives on the crystal growth, properties and crystalline perfection of tris(thiourea)copper(I) chloride (TCC) crystals

The influence of inorganic Co(II) and organic (urea) additives on the properties and crystalline perfection of TCC single crystals grown at 30 °C by slow evaporation solution grown technique (SEST) is investigated. The stoichiometry of the as-grown anhydrous complex crystal was confirmed by elemental (C, H, N and S; CHNS) analysis. Incorporation of Co(II) into the crystal lattice is well confirmed by EDS and chemical tests. Powder XRD profiles of Co–TCC reveal slight changes in intensity patterns of the spectra. FT-IR studies, particularly for heavily Co(II)-doped TCC, reveal small vibrational changes. Second harmonic generation (SHG) studies reveal that TCC is NLO inactive and doping does not lead to any SHG. SEM reveals changes in surface morphology as a result of doping. Urea doping results in red shift in PL spectrum and it very much suggests the complex formation. The addition of low quantity of dopants into the crystal through the aqueous growth medium improves the crystalline perfection to a great extent as evidenced from high-resolution X-ray diffraction (HRXRD) studies. However, high dopant concentration leads to the formation of structural grain boundaries leading to deterioration of crystalline perfection. It appears that some part of the doped Co(II) occupies substitutional positions because of close atomic/ionic radii with that of the host metal. The interstitial site occupancy is predominant in the case of urea dopant.

Evidence for kinks in structural and thermodynamic properties across the forsterite–fayalite binary from thin-film IR absorption spectra

Infrared absorbance spectra over ∼100 to 1,800 cm−1 were collected from optically thin films of 21 samples with compositions spanning the forsterite–fayalite binary. Polarization information from previous specular reflectance data on end-members was used in tracing the peaks across the entire binary. Peak positions (νi) were constrained by Lorentzian decompositions. Fitting also constrained widths for singlet peaks but for doublets and triplets, variation in νi with composition among the constituent polarizations alters widths from intrinsic. Because film thicknesses of 0.6–1.4 μm were estimated, our band strengths are approximate; however, relative intensities should be correct. Only for a few peaks does νi vary smoothly across the entire binary; instead, distinct linear trends exist for Fe- and Mg-rich olivines. Discontinuities and kinks in νi(X) occur at X = Mg/(Fe + Mg) = 0.7 and are accompanied by a change in intensity patterns. This interesting behavior was not revealed in previous spectra of powder dispersions. The contrasting character of IR vibrations for Fe- and Mg-rich olivines is inferred to arise from structural variations because (1) frequency is related to bond length, (2) other factors affecting frequency (cation mass and probably bonding type) vary linearly across the binary, and (3) available data on unit cell parameters are consistent with distinct trends for forsterites and fayalites. Vibrational components of heat capacity (C V) and enthalpy (H) calculated from νi, were found to be slightly more negative than linear interpolations between values for forsterite and fayalite. Our computations give smaller negative excesses from ideality in H than do previous calorimetric measurements, but are equal within experimental uncertainties.

High-Pressure Vibrational Spectroscopy of Energetic Materials: Hexahydro-1,3,5-trinitro-1,3,5-triazine

Vibrational spectroscopy has been used to investigate the room-temperature high-pressure phases of the energetic material hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The pressure-induced alterations in the spectral profiles were studied in a compression sequence to 30.2 GPa using Raman spectroscopy and to 26.6 GPa using far-infrared spectroscopy. At pressures near 4.0 GPa, several changes become immediately apparent in the Raman spectrum, such as large frequency shifts, mode splittings, and intensity changes, which are associated with a phase transition from alpha-RDX to gamma-RDX. Our study extends the kinetic stability of gamma-RDX to pressures near 18.0 GPa. Evidence for a new phase was found at pressures between 17.8 and 18.8 GPa and is based on the appearance of new vibrational bands and associated changes in intensity patterns. The new phase has vibrational characteristics that are similar to those of beta-RDX, suggesting the two polymorphs share a related crystal structure.

Second Harmonic Generation from Si1-xGex Epitaxial Films with a Vicinal Face: Film Thickness Dependence

We have observed optical second harmonic generation in Si1-x Gex (x=0.685) crystalline films grown on Si(001) substrates. The substrates are oriented 4 degrees off the [001] direction rotated about the [100] axis. We have measured the SH intensity as a function of the film thickness and the sample rotation angle about the surface normal. The intensity pattern changes as the film thickness is varied from 110 nm to 58 nm. For the film thickness of 110 nm the intensity curve as a function of the rotation angle has three maxima. This angular pattern can be reproduced by a model that includes the effect of interference between the surface and bulk second harmonic amplitudes. For the film thickness of 58 nm the angular pattern has only one maximum. In this case the surface SHG dominates the observed intensity and no interference effect is observed.

Vibration and sound radiation of a piano soundboard

Vibration and radiation characteristics of a piano soundboard for a 6-ft grand piano are investigated by use of modal analysis and surface-intensity methods. The mode shapes and frequencies of six resonances below 200 Hz are shown, and their relations to intensity patterns are discussed. The intensity pattern changes in a very complex manner as the frequency varies. The radiation efficiency below 80 Hz is very low. Sound is radiated fairly efficiently in the frequency range of 100 Hz–1 kHz, and very efficiently above 1.4 kHz. The results indicate that it is very important to make the input power to the soundboard as constant as possible with respect to the driving point as well as the driving frequency, in order to achieve a smooth change of sound power output from note to note.

Determining motion of image curves from local pattern changes

The instantaneous velocity field along a curve satisfies a differential equation. Given the velocity at one point of the curve and the dilatation at every point, the correct velocity field can be obtained by integrating local intensity pattern changes. Usually one has no information about the dilatation of the curve. We therefore apply a minimum dilatation principle yielding the correct velocity field in the case of a nonelastic motion and a two-dimensional rigid motion with expansion. The velocity field can be calculated by applying a propagation algorithm which does not involve iterations and which allows the use of parallel techniques to implement it. In the tests we used natural images with artificially generated motion.