Eduardo J. S. Fonseca

Fraunhofer diffraction of light with orbital angular momentum by a slit

We study the Fraunhofer diffraction problem while taking into account the orbital angular momentum of light. In this case, the phase singularity of the light beam is incident on the slit in two different cases: in one, it is incident slightly above the slit, and in the other it is centered on the slit. We observed that the symmetry and the fringe formation in the interference pattern strongly depend on the amount of orbital angular momentum and the slit position in relation to the beam.

Effects of pseudothermal light source's transverse size and coherence width in ghost-interference experiments.

Ghost interference is experimentally investigated by varying the pseudothermal light sources transverse size and coherence width. Our results show that by increasing the transverse size of the source the quality of the interference pattern is improved, while the visibility is reduced. On the other hand, by increasing the coherence width of the source, the visibility of the interference pattern is improved, while the quality is reduced. These experimental results corroborate previous theoretical results.

Engineering a square truncated lattice with light's orbital angular momentum

We engineer an intensity square lattice using the Fraunhofer diffraction of a Laguerre-Gauss beam by a square aperture. We verify numerically and experimentally that a perfect optical intensity lattice takes place only for even values of the topological charge. We explain the origin of this behavior based on the decomposition of the patterns. We also study the evolution of the lattice formation by observing the transition from one order to the next of the orbital angular momentum varying the topological charge in fractional steps.

Born's rule and the interference of photons with orbital angular momentum by a triangular slit

We use photon OAMs two-dimensional properties to extend the double-slit to a two-dimensional triple-slit configuration in the shape of an equilateral triangle, obtaining a bidimensional triangular interference pattern at photon level, whose size depends on the OAM amount. We also show that for this pattern, in contrast with the parallel two- and three-slit cases, the azimuthal phase plays a fundamental role, being undistinguishable from the path phase. Our results confirm that only pairs, here associated to path and azimuthal phases, contribute to the two-dimensional photon detection probability, as established by Borns rule.

Localized cutaneous mucinosis as a presentation of secondary extramedullary cutaneous plasmacytoma

SIR, Generalized pustular psoriasis (von Zumbusch type) is often induced by abrupt termination of systemic corticosteroid therapy, bacterial infections, pregnancy, oral contraceptives and drugs such as b-blockers or antimalarials. It is characterized by groups of sterile pustules arising on erythematous skin with episodes of fever and subsequent waves of new pustules. Erythroderma, weight loss, muscle weakness, leucocytosis, hypocalcaemia and an increased erythrocyte sedimentation rate are associated with the disease. Besides elimination of provoking factors, first-line treatment is with systemic retinoids, occasionally combined with photochemotherapy. However, without adequate treatment, death may occur in one-third of cases. In 1996, a 76-year-old woman experienced a first manifestation of skin lesions which were histologically shown to be psoriasis vulgaris. The skin lesions responded to local treatment. Six years later, she developed a sudden eruption of severe generalized pustular psoriasis. This was treated with acitretin (up to 1 mg kg), with only partial response. Due to sudden agranulocytosis this therapy was terminated, resulting in immediate relapse. As subsequent therapy with methotrexate (up to 15 mg weekly) led to only insufficient control, ciclosporin (up to 3 mg kg) was added. Again, severe leucopenia occurred. Discontinuation of methotrexate resulted in granulocyte recovery, but ciclosporin alone was unable to suppress new eruptions and was stopped because of increased blood pressure. Dapsone 1 mg kg also caused immediate agranulocytosis, accompanied by an impressive clearance of cutaneous symptoms. However, leucocyte recovery was paralleled by a drastic deterioration of skin conditions. Following reports of improvement of plaque-type psoriasis in a number of patients by antitumour necrosis factor (TNF)-a antibody treatment, we initiated therapy with infliximab 5 mg kg as a single dose. Obvious improvement of the skin lesions was observed within 12 h, with complete disappearance of pustules and erythema within 48 h. After 1 week, signs of pustular psoriasis recurred and infliximab was given again. Again, total remission of skin lesions occurred within 48 h. This time, remission was lasting, with erythema and tiny pustules reappearing only 3 months later. A third course of infliximab was given and complete remission was observed within the following days. After 3 months a few erythematous macules bearing some pustules recurred, but were easily controlled by local therapy. The treatment was well tolerated and no adverse effects, including concomitant infections, decreased blood granulocytes or other laboratory changes, have been recorded. The central role of neutrophils in pustular psoriasis is deduced not only from the clinical picture of multiple sterile pustules on inflamed skin, but also from the obvious clearing of skin lesions during episodes of agranulocytosis in this case. The repeated critical decrease in granulocytes in our patient is ascribed mainly to toxic effects of the various drugs. Cyclical neutropenia can be excluded by the fact that blood cell counts showed no abnormalities during the last 6 months. TNF-a is a decisive mediator for the activation and tissue invasion of neutrophil granulocytes, e.g. by the induction of adhesion molecules on vascular endothelial cells. Thus TNF-a-neutralizing antibodies should provide a rational tool in the treatment of psoriasis, not only for chronic plaque type, but also for possibly life-threatening generalized pustular psoriasis, as has recently also been reported by others. This may especially apply if other treatment modalities are contraindicated or prove to be ineffective.

Unveiling square and triangular optical lattices: a comparative study

We study square and triangular optical lattice formation using a diffraction technique with light-possessing orbital angular momentum (OAM). We demonstrate that it is possible to use Fraunhofer diffraction of light by a square aperture to unveil OAM about two times bigger than would be possible with a triangular aperture. We notice that the pattern remains truncated until a topological charge (TC) equal to 20 with good precision. Even though a square pattern cannot be used to determine the TC sign, it is possible to measure high order of the modulus and sign of the TC up to 20, combining patterns of the triangular and square apertures.

Space-time break-up in the self-focusing of ultrashort pulses

We investigate the effect of rapidly varying perturbations on the initial stage of the three-dimensional propagation of ultrashort pulses through a nonlinear dispersive medium, in the limit and beyond the slowly varying envelope approximation. We have found a space-time coupling effect which distorts and reduces the range for which sidebands appear on far-field and temporal spectrum.

Weak signal pulse compression and amplification through stimulated Raman scattering and cross-phase modulation in optical fibers

Abstract Simulataneous amplification and temporal compression of low intensity signal pulses of a few μWs peak powers in single-mode optical fibers is reported. The process was achieved by means of the combined effects of synchronous Raman amplification and cross-phase modulation induced chirp on a weak signal copropagating with a strong pump pulse in an optical fiber. Experimental results agree quite well with numerical simulations.

Ouricuri (Syagrus coronata) fiber: a novel biosorbent to remove methylene blue from aqueous solutions

In this work, the potential of ouricuri (Syagrus coronata) fiber as a novel biosorbent to remove methylene blue (MB) from aqueous solutions was investigated. The fiber was prepared and characterized according to the fundamental features for adsorption. A 23 experimental design was used to evaluate the effects of adsorbent dosage (M), fiber diameter (D) and agitation (A) on the adsorption capacity. In the more adequate conditions, kinetic and equilibrium studies were performed. The experimental design results showed that M = 10 g L-1), D = 0.595 mm and A = 200 rpm were the more adequate conditions for MB adsorption. Based on the kinetic study, it was found that the adsorption process was fast, being the equilibrium was attained at about 5 min, with 90% of color removal. The isotherm was properly represented by the Sips model, and the maximum adsorption capacity was 31.7 mg g-1. In brief, it was demonstrated that ouricuri fiber is an alternative biosorbent to remove MB from aqueous media, taking into account the process efficiency and economic viewpoint.

Self-reconfiguration of a speckle pattern

It is well known that coherent Bessel beam, a nondiffracting class of beam, possesses the ability of self-reconstructing or self-healing in the presence of obstacles. Here, we generated partially coherent Bessel and Gaussian beams using a spatial light modulator and studied the speckle pattern intensity in propagation after some speckles were blocked. We demonstrated that these partially coherent beams are unexpectedly robust against scattering by objects, overcoming the coherent Bessel beam and remaining independent of any special class of partially coherent beams.