Author: RUBEN RAMOS GARCIA

Selective photodeposition of zinc nanoparticles on the core of a single-mode optical fiber

RUBEN RAMOS GARCIA (2013)

An experimental and theoretical study about selective photodeposition of metallic zinc nanoparticles onto an optical fiber end is presented. It is well known that metallic nanoparticles possess a high absorption coefficient and therefore trapping and manipulation is more challenging than dielectric particles. Here, we demonstrate a novel trapping mechanism that involves laser-induced convection flow (due to heat transfer from the zinc particles) that partially compensates both absorption and scattering forces in the vicinity of the fiber end. The gradient force is too small and plays no role on the deposition process. The interplay of these forces produces selective deposition of particles whose size is directly controlled by the laser power. In addition, a novel trapping mechanism termed convective-optical trapping is demonstrated.

Article

Fiber optics, infrared Photothermal effects Optical tweezers or optical manipulation Laser trapping CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Collision of propagating vortices embedded within Airy beams

Carmelo Rosales-Guzmán VALERIA RODRIGUEZ FAJARDO RUBEN RAMOS GARCIA (2013)

We present the engineered collision of two curvilinear propagating optical vortices each embedded in the main lobe of an Airy beam. Two cases are analyzed: same and opposite unitary topological vortex charge. We observed experimentally that in the first case the main vortices repel each other and remain separated after the collision. On the contrary, in the second case an annihilation of the main vortices occurs. Our experimental observations are reinforced by numerical simulations showing that the conservation of topological charge dictates the vortex dynamics.

Article

Collision of propagating Optical vortices Airy beam CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Amorphous silicon-liquid crystals device forphotonic applications

ÁNGEL FUENTES GARCIA María del Carmen Grados Luyando JULIO CESAR RAMIREZ SAN JUAN RUBEN RAMOS GARCIA (2013)

We demonstrate that an hydrogenated amorphous silicon (a:SiH)-liquid crystals hybrid device could be used for the recording of high resolution (0.8-2 µm) dynamic holograms. A maximum diffraction efficiency of 3.3% was obtained at low power (1.5 mW) He-Ne laser. The nonlinear refractive index change at 0.6 W/cm2 is n2~1x10−2 cm2 /W, although small compared to that obtained in dye-doped liquid crystal, is equal to the reported in pure liquid crystal although with much higher power density (~50 W/cm2 ). The device operates in the red to near-infrared part of the spectrum which makes it attractive due to its potential applications in telecommunications and military applications.

Article

Nonlinear optics Diffraction gratings Holography Liquid crystals CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA

Effects of speckle/pixel size ratio on temporal and spatial speckle-contrast analysis of dynamic scattering systems: Implications for measurements of blood-flow dynamics

JULIO CESAR RAMIREZ SAN JUAN Emilia Margarita Méndez Aguilar NOEMI JASMIN SALAZAR HERMENEGILDO ÁNGEL FUENTES GARCIA RUBEN RAMOS GARCIA (2013)

Laser Speckle Contrast Imaging (LSCI) is an optical technique used to generate blood flow maps with high spatial and temporal resolution. It is well known that in LSCI, the speckle size must exceed the Nyquist criterion to maximize the speckle's pattern contrast. In this work, we study experimentally the effect of speckle-pixel size ratio not only in dynamic speckle contrast, but also on the calculation of the relative flow speed for temporal and spatial analysis. Our data suggest that the temporal LSCI algorithm is more accurate at assessing the relative changes in flow speed than the spatial algorithm.

Article

Speckle imaging Velocimetry Speckle CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA