Anderson M. Amaral

Characterization of topological charge and orbital angular momentum of shaped optical vortices

Optical vortices (OV) are usually associated to cylindrically symmetric light beams. However, they can have more general geometries that extends their applicability. Since the typical experimental characterization methods are not appropriate for OV with arbitrary shapes, we discuss in this work how the definitions of the classical orbital angular momentum and the topological charge can be used to retrieve these informations in the general case. The concepts discussed are experimentally demonstrated and may be specially useful in areas such as optical tweezers and plasmonics.

Shaping optical beams with topological charge

We show that by spatially arranging topological charges on a phase mask, it is possible to shape the spatial intensity profile of vortex beams in a controlled manner. As proof-of-principle experiments, we generated vortex beams with the spatial shape of straight lines, corners, and triangles. Potential applications for shaped beams include selective excitation of plasmonic modes, geometrically tunable Bose-Einstein condensates, and optical tweezers.

Measurements of the nonlinear refractive index in scattering media using the Scattered Light Imaging Method - SLIM

The Scattered Light Imaging Method (SLIM) was applied to measure the nonlinear refractive index of scattering media. The measurements are based on the analysis of the side-view images of the laser beam propagating inside highly scattering liquid suspensions. Proof-of-principle experiments were performed with colloids containing silica nanoparticles that behave as light scatterers. The technique allows measurements with lasers operating with arbitrary repetition rate as well as in the single-shot regime. The new method shows advantages and complementarity with respect to the Z-scan technique which is not appropriate to characterize scattering media.

D4σ curves described analytically through propagation analysis of transverse irradiance moments.

The far-field changes in the beam width of an intense light beam propagating inside optical materials are investigated aiming the measurement of the nonlinear properties of the samples. The beam width is characterized in this Letter in terms of the transverse irradiance moments (TIMs) that allow an accurate description of the beam interaction and propagation. TIMs are rigorously related to the paraxial beam propagation parameters, and it is also possible to consider elliptical and astigmatic beams. Experimental data with very good signal-to-noise ratio were obtained for the reference materials carbon disulfide and fused quartz.

Analytical approach to nonlinear refraction index measurements with the D4σ technique

We obtained analytical expressions for the far-field beam width due to elliptical and astigmatic beams propagating inside Kerr media, and performed experiments with CS2 and silica. A good agreement between theory and experiment was found.

Analytical Description of Nonlinear Refraction Index Measurements with the D4\sigma Technique

We obtained analytical expressions for the far-field beam width due to elliptical and astigmatic beams propagating inside Kerr media, and performed experiments with CS2 and silica. A good agreement between theory and experiment was found.

Non-cylindrical optical vortices

Abstract The spatial intensity profile of vortex beams may be shaped by spatially arranging topological charges on a phase mask. In our experiments, we produced and characterized vortex beams shaped as straight lines, corners and triangles.

Shaping Optical Vortex Beams with Topological Charge

We show that it is possible to shape the spatial intensity profile of vortex beams by spatially arranging topological charges on a phase mask. In our experiments, we generated vortex beams shaped as straight lines, corners and triangles.

Effective high-order susceptibilities in composites containing ellipsoidal nanoparticles and nanoshells

Expressions for the effective nonlinear susceptibilities are derived for nanocomposites containing ellipsoidal nanoparticles and nanoshells. The intrinsic third- and fifth-order contributions are considered for the nanoinclusions. The field enhancement is determined for silver particles.