Author: JULIO CESAR RAMIREZ SAN JUAN

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