Alcenísio J. Jesus-Silva

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.

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.

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.

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.

Characterizing coherence vortices through geometry

We produce coherence vortices experimentally and numerically due to the orbital angular momentum of light beams and study the dependence of their bright ring area and dark region on their different orders. This is a linear dependence with a slope proportional to the bright ring area or dark area. We show that it is possible to estimate any order of coherence vortices, including fractional orders, just by calculating the bright ring area or dark area of the vortices for some specific parameters of the incident beam.

Strong correlations between incoherent vortices

We establish a correlation rule of which the value of the topological charge obtained in intensity correlation between two coherence vortices is such that this value is bounded by the topological charge of each coherence vortex. The original phase information is scrambled in each speckle pattern and unveiled using numerical intensity correlation. According to this rule, it is also possible to obtain a coherence vortex stable, an integer vortex, even when each incoherent vortex beam is instable, non-integer vortex.

Study of the birth of a vortex at Fraunhofer zone

We analytically and experimentally study the Fraunhofer diffraction of an optical vortex beam possessing noninteger values of the azimuthal index. We show that the Fraunhofer diffraction of this beam presents the birth of a vortex at α=n+ε, where n is an integer number and ε is a small fraction. We discuss this behavior on the basis of the born vortex movement from a position of low intensity to high intensity when α is increased of an integer number in fractional steps of ε.

Robustness of a coherence vortex

We study, experimentally and theoretically, the behavior of a coherence vortex after its transmission through obstacles. Notably, we find that such a vortex survives and preserves its effective topological charge. Despite suffering changes on the modulus of the coherence function, these changes disappear during propagation.

Measurement of the orbital angular momentum at photon level via the spatial probability distribution

We demonstrate that by diffracting light at single photon level with orbital angular momentum (OAM) by an equilateral triangular aperture, it is possible to determine their OAM amount by simply counting the number of maxima in the side of a generated triangular shaped hexagonal lattice in the spatial photon probability distribution. The sign of the OAM is obtained by the orientation of the latticed triangle. We also show that by changing the aperture size it is possible to discriminate OAM state superpositions.