Yezid Torres Moreno

Generation of Perfect Optical Vortices by Using a Transmission Liquid Crystal Spatial Light Modulator

We have experimentally created perfect optical vortices by the Fourier transformation of holographic masks with combination of axicons and spiral functions, which are displayed on a transmission liquid crystal spatial light modulator. We showed theoretically that the size of the annular vortex in the Fourier plane is independent of the spiral phase topological charge but it is dependent on the axicon. We also studied numerically and experimentally the free space diffraction of a perfect optical vortex after the Fourier back plane and we found that the size of the intensity pattern of a perfect optical vortex depends on the topological charge and the propagation distance.

Sagnac Interferometer Based Generation of Controllable Cylindrical Vector Beams

We report on a novel experimental geometry to generate cylindrical vector beams in a very robust manner. Continuous control of beams’ properties is obtained using an optically addressable spatial light modulator incorporated into a Sagnac interferometer. Forked computer-generated holograms allow introducing different topological charges while orthogonally polarized beams within the interferometer permit encoding the spatial distribution of polarization. We also demonstrate the generation of complex waveforms obtained by combining two orthogonal beams having both radial modulations and azimuthal dislocations.

Seguimiento de una reacción fotocatalítica modelo expuesta a la propagación de la superposición de dos vórtices ópticos con momento angular orbital entero definido y opuesto, por medio de espectroscopía UV-VIS

El presente articulo realiza un analisis espectral de un conjunto de ensayos efectuados sobre una reaccion foto catalitica modelo basada en la actividad de fenol disuelto en agua con oxido de titanio dopado como catalizador e irradiada con un haz de luz coherente, cuyo frente de onda corresponde a la superposicion de dos vortices opticos con momento angular orbital entero definido de sentido opuesto.Como primera instancia se describe la arquitectura opto electro-quimica empleada en el estudio, luego se selecciona por medio de un barrido discreto de haces propagados de 405 y 450 nm, la longitud de onda adecuada para proyectar los vortices opticos sobre la muestra. Por ultimo se realiza el tratamiento y analisis de las senales adquiridas a traves de espectrofotometria UV de las muestras irradiadas con las distribuciones espaciales de luz de interes controladas por un holograma generado por computador.

Diffracted optical vortices by an angular aperture

The measurement of the topological charge of laser beams with orbital angular momentum (OAM) is key to many applications like deciphering information encoded in several channels. Current techniques useful for that purpose are interferometry, diffraction through different poligonal apertures like triangular or pentagonal and, azimuthal and radial decomposition. A less explored issue is the diffraction of OAM beams through circular sectors. Jack et al. studied the angular diffraction of Gaussian beams (whose OAM is null) through a circular sector. By means of a Fourier transform of the truncated Gaussian beam they showed that the orbital angular momentum spectrum of the transmitted beam has a sinc-shaped envelope centered at zero orbital angular momentum, the width of which increases as the central angle of the circular sector decreases. We analyze here the spectrum of a laser beam with integer OAM that has been diffracted by a circular sector. We present results for circular sectors of different central angles. For circular π-sector, we also study the influence of the transmittance in the OAM spectra of the transmitted beam, using straight borders of nanometric thin films of titanium oxide with different thicknesses. We use a spatial light modulator with a fork hologram placed on to generate the incoming OAM beam and measure the evolution of the intensity profile of the diffracted beam as it propagates away from the circular sector. The spectra of the diffracted OAM beams are shown numerically and experimentally to have a sinc shaped envelope centered at the OAM value of the incoming OAM wave.

Coherence modulation at the photon-counting level: A new scheme for secure communication

When operated at the photon-counting level, coherence modulation can provide quantifiably secure binary signal transmission between two entities, security being based on the nonclonability of photons.

Far-field diffraction pattern of a Bessel-Gauss beam through a pentagonal aperture

We report through of computer simulations and experimental measurements that the dark spots number in the pattern of the far-field diffraction intensity distribution by a non-equilateral pentagonal aperture is just equal to the integer value of the used Bessel-Gauss beam topological charge.