Author: JULIO CESAR RAMIREZ SAN JUAN
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.
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.