Arturo Olivares-Pérez

Nonredundant calculations for creating digital Fresnel holograms

In this paper we propose an alternative technique for producing digital Fresnel holograms. The evaluation of a diffraction pattern in a wide region is implemented in such a way as to avoid redundant calculations and preserve the precision. Because of the symmetry of the kernel, the complex amplitude is calculated at four points in the registration plane simultaneously. This algorithm decreases the required CPU time 4 times with respect to direct calculation. The digital Fresnel hologram is numerically and optically reconstructed, and some qualitative comparisons are made.

Holograms in polyvinyl alcohol photosensitized with CuCl 2 (2H 2 O)

We propose the use of polyvinyl alcohol photosensitized with copper chloride dihydrated CuCl2(2H2O) as a photosensitive material for recording holographic gratings. We obtained different dissolutions changing concentration of photosensitive agent and varying their pH factor, refraction index, and optical density for each sample. We registered diffraction gratings by holographic methods. The behaviors of diffraction efficiency parameters of holographic gratings regarding the concentration of a photosensitive agent were analyzed. We show there exists a correspondence between the diffraction efficiency parameter with concentration change of CuCl2(2H2O). The low toxicity of this holographic recording material as well as its peculiar behavior, photosensitivity, and ability to conduct electricity, makes it attractive for production diffractive optical elements with bio-polymers.

EFFECTS ON PROFILE DEPTH OF CHANGES IN THE THICKNESS OF THE PHOTORESIST LAYERS

We propose a model to describe the behavior of the absorption profile as a function of the thickness changes of the photoresist layers (Shipley 1350-J), used to make high-quality holographic elements. We also show that the surface topology of the substrate is an important parameter that modulates the layers thickness on the substrate. We obtain a depth modulation Δd in the exposure time (assuming a uniform irradiance), which is brought about by changes in the thickness of the photoresist layers at different points on the substrate; the thickness parameter is a function of the absorption coefficient of the photoresist.

Real-time holographic gratings modulate with voltage by different thickness film

The holographic gratings on photopolymer films are studied by three different thicknesses for samples A, B, and C. The photopolymer emulsion is prepared with potassium dichromate and nickel (II) chloride hexahydrate in polyvinyl alcohol matrix. The evolution of diffraction efficiency is evaluated during holographic recording with and without voltage as a function of energy exposure by changing the thickness. The curves of diffraction efficiency reach a peak when the films are continuously exposed to energy for a period of time. Sample B obtains the highest diffraction efficiency

Magnification effect and color blur behavior in holography

This paper describes the spatial behavior of the hologram image as a function of the geometric setup used in the recording and reconstruction steps. Given the equation of the holographic image and using paraxial theory and the synthetic division method, values of the longitudinal and lateral magnification are obtained. The location and magnification of the holographic image are found when the distance between the holographic plate and the object is changed. For white light reconstruction and 3-D scenes the effect of color blur can be expressed in terms of the parameters associated with the optical system that forms the image on the hologram and the recording geometry.

Fish gelatin and ammonium dichromate as photosensitive film

In this work we propose a phase material based on fish gelatin from Norland Products© mixed with ammonium dichromate deposited on a glass substrate. The photosensitive film has 110 mm thickness. In this material we record low frequency (264 lines/mm) holographic gratings using a λ=532 nm from an Ar laser and reconstruct the image with λ=594 nm from a He-Ne laser. The diffraction efficiency is approximately15% for the first order. The material no requires developing process and is very easy to make. Experimental results are shown.

Characterization of a PDLC mixed with crystal violet dye

We show the optical characterization of a Polymer Dispersed Liquid Crystal which was made mixing Norland Optical Adhesive No. 65®, nematic liquid crystal and crystal violet dye, deposited between two glass substrates with indium tin oxide (ITO) as electrodes. In this device, we recorded low frequency (104 lines/mm) holographic gratings made with the interference of two beams from an Ar laser at 515 nm in emission line. We measured the diffraction efficiency of the gratings obtaining 2% when the grating was read with a beam from a He-Ne laser at 612 nm.

Replication of Holograms with Corn Syrup by Rubbing

Corn syrup films are used to replicate holograms in order to fabricate micro-structural patterns without the toxins commonly found in photosensitive salts and dyes. We use amplitude and relief masks with lithographic techniques and rubbing techniques in order to transfer holographic information to corn syrup material. Holographic diffraction patterns from holographic gratings and computer Fourier holograms fabricated with corn syrup are shown. We measured the diffraction efficiency parameter in order to characterize the film. The versatility of this material for storage information is promising. Holographic gratings achieved a diffraction efficiency of around 8.4% with an amplitude mask and 36% for a relief mask technique. Preliminary results using corn syrup as an emulsion for replicating holograms are also shown in this work.

Analysis of voltage effect on holographic gratings by modulation transfer function

The experimental data allow us to determine the imaging quality of holographic gratings with photosensitive film using organic material based on a polyvinyl alcohol matrix doped with potassium dichromate and nickel (II) chloride hexahydrate. The diffraction efficiency is estimated by different spatial frequencies, and the readout image quality is analyzed by the modulation transfer function. The experiment is carried out, with and without voltage application, at different spatial frequencies to obtain the image quality of photosensitive film.

Refraction indexes of the polyester film 3M PP2500

In this work we describe an experimental technique to measure the refraction index of the 3M PP2500 film which has good behavior as quarter wave retarder plate for λ=633 nm. This technique is achieved when two perpendicular linearly polarized beam from a Wollaston prism are incident on the thickness of the film. The beams were incident parallel to the fast axis to measure the ordinary refraction index and parallel to the slow axis to measure the extraordinary refraction index. Some experimental results are shown.