Sergio Calixto

Dry polymer for holographic recording.

A dry polymeric mixture rendered red sensitive with a dye has been used to record interference gratings and holograms. Diffraction efficiencies of ~10% can be attained with exposures of ~94 mJ/cm(2). If necessary the reading step can be done just after the exposure or after a fixing step performed with light from a mercury lamp.

Capillary refractometer integrated in a microfluidic configuration

We propose a microfluidic method to measure the refractive index of liquids. This method is based on the dynamic focusing by a capillary when liquids with different refractive indexes are inserted into it. Fabrication of such a refractometer has been done by encapsulating two fibers and a capillary. A calibration method is proposed.

DRY PHOTOPOLYMER FILMS FOR COMPUTER-GENERATED INFRARED RADIATION FOCUSING ELEMENTS

A new technological approach makes fabrication of relief computer-generated focusing elements for IR radiation by use of a dry photopolymer recording material possible. The formation of a relief structure by self-development takes place in the dark, subsequent to the holographic illumination, without wet processing. Consequently these diffractive elements exhibit low surface scattering. The formation of a surface wave of the monomer along the light-darkness boundary is observed for the first time to our knowledge and confirms the previously proposed thermodynamic model of the mechanism of the hologram formation in photopolymerizable layers. Dye-sensitized polymerization of acrylamide is found to produce nonlinearity of the relief recording. At least partial compensation of this nonlinearity is attained by the introduction of appropriate corrections into the computer-generated amplitude function. A diffraction efficiency of ~ 55% is obtained for CO(2) laser radiation (λ = 10.6 µm).

Optofluidic variable focus lenses

Here we propose optofluidic spherical microlenses that can change their focal distance by varying the refractive index of the liquid that composes them. These lenses are fabricated in the bulk of a polymeric mixture. Results of a characterization study of the profile of the lenses, the image forming capability, and the behavior of the focal distance as a function of the refractive index are presented. Ionic liquids are suggested as a source of liquids useful for fabricating this type of lens.

Relief optical microelements fabricated with dichromated gelatin

Relief microlenses and micromirrors are fabricated in dichromated gelatin layers. Microelements typically have diameters of approximately a few hundred micrometers and have focal distances ranging from 4 to 15 mm.

Micromirrors and microlenses fabricated on polymer materials by means of infrared radiation

A simple method for fabricating micromirrors and microlenses on polymer substrates is presented. Microelements with diameters of approximately several hundred micrometers and f numbers ranging from 3 to 11 have been produced.

Rod and spherical silica microlenses fabricated by CO2 laser melting.

The fabrication and testing of glass microlenses with rod and spherical shapes are described. The sizes of the lenses range from tens of micrometers to several millimeters. The surfaces of the lenses were fabricated by the melting method. These surfaces have been studied by several methods. The theoretical behavior of the lenses was investigated by ray tracing. Some applications of the lenses are presented.

Silicone microlenses and interference gratings

Interference gratings, plano-convex microlenses, and spherical microlenses have been made in silicone. Lenses were fabricated by the melting method. Two substrates have been tried: glass and Teflon. The latter substrate lets us fabricate low-f-number lenses. We made spherical microlenses by placing pieces of silicone near a thermal source and studied resolution of the lenses by investigating the images they gave of a test chart. We made low-spatial-frequency gratings by recording interference patterns and studied parameters involved in the recording. A study of the profile of the gratings and lenses was done with a mechanical surface analyzer.

Infrared recording with gelatin films

Gelatin films glued to an O-ring are proposed as a new procedure to record interference patterns when a CO(2) laser is used as an infrared light source. With this method the unwanted effects given by asubstrate, on which the thin recording film is laid, are avoided. To characterize the medium, interferometric studies including the recording of diffraction gratings have been done. Diffraction efficiencies of ~30% have been obtained when coherent red light (0.6328-microm wavelength) was sent normally to the gratings. An example of an infrared recorded hologram is shown.

High topographical accuracy by optical shot noise reduction in digital holographic microscopy

In this work, we present a new method to reduce the shot noise in phase imaging of digital holograms. A spatial averaging process of phase images reconstructed at different reconstruction distances is performed, with the reconstruction distance range being specified by the numerical focus depth of the optical system. An improved phase image is attained with a 50% shot noise reduction. We use the integral of the angular spectrum as a reconstruction method to obtain a single-object complex amplitude that is needed to perform our proposal. We also show the corresponding simulations and experimental results. The topography of a homemade TiO2 stepwise of 100 nm high was measured and compared with the atomic force microscope results.