Holographic Recording Material Research Articles

Near-real-time phase difference amplification using multiple-beam interferometry and a liquid-crystal-phase-only spatial light modulator

Phase difference amplification is a technique used to produce a fringe contour map in which the optical path difference between one fringe and the next is a fraction of a wavelength. To ensure high accuracy of the technique, it is usually necessary to generate interference between the high-order diffracted beam and its conjugate beam by means of a holographic recording material that provides sufficiently large nonlinearity to record the original fringe pattern from the test object. This paper shows that not only the nonlinearity of the recording material, but also multiple-beam interference, can be used to produce high-order diffracted beams. A Tolansky-type multiple-beam interferometer has been used in conjunction with an optically addressed liquid-crystal spatial light modulator to set up a system that functions in near real time and provides high accuracy.

New Azobenzene Chromophores as Monomers for Synthesis of Polyesters

Two new azo-chromophores: 2,4-dihydroxy-4’-nitroazobenzene and 2,4-dihydroxy-4-azo-(4’-nitroazobenzeno)benzene have been prepared. These diols have been applied as monomers for polyesters synthesized in condensation with diacid chlorides: isophthaloyl chloride and sebacoyl chloride. The copolymers consist of mixture of two new diols and chlorides have been obtained as well. The polymers were identified by infrared and elemental analysis. Character of polymers was determined using X-Ray spectroscopy. Thermal properties of polyesters such as glass transition temperature and thermal stability were investigated using differential scanning calorimetry (DSC) method and thermogravimetric analysis. These polymers with azobenzene groups could find potential applications as holographic recording materials. The preliminary investigations of optical grating recording were carried out.

Low spatial frequency characterization of holographic recording materials applied to correlation

Accurate recording of computer-generated holograms (CGH) on a phase material is not a trivial task. The range of available phase materials is large, and their suitability depends on the fabrication technique chosen to produce the hologram. We are particularly interested in low-cost fabrication techniques, easily available for any lab. In this work we present the results obtained with a wide variety of phase holographic recording materials, characterized at low spatial frequencies (≤32 lp mm−1) which is the range associated with the technique we use to produce the CGHs. We have considered bleached emulsion, silver halide sensitized gelatin (SHSG) and dichromated gelatin. Some interesting differences arise between the behaviour of these materials in the usual holographic range (}1000\ntilde {\mathrm {lp\ntilde mm^{-1}}}$>>1000 lp mm−1), and the low-frequency range intended for digital holography. The ultimate goal of this paper is to establish the suitability of different phase materials as the media to generate correlation filters for optical pattern recognition. In all the materials considered, the phase filters generated ensure the discrimination of the target in the recognition process. Taking into account all the experimental results, we can say that SHSG is the best material to generate phase CGHs with low spatial frequencies.

Optimization of a photopolymerizable holographic recording material based on polyvinylalcohol using angular responses

Abstract Acrylamide-based holographic recording materials have significant advantages and the composition of these materials has been optimized in terms of energetic sensitivity and diffraction efficiency. As a result, diffraction gratings with an efficiency of almost 80% for energetic exposures of 35 mJ/cm2 and a spatial frequency of 1000 lines/mm in photosensitive films 65 μm thick have been obtained. In this paper we present the effects of intensity, thickness, and variation in the concentration of each component by studying the angular responses of the diffraction gratings recorded in each composition.

Photochemical modulation of alignment of liquid crystals and photonic applications

The recent highlights in the photoinduced modulation of the liquid-crystalline (LC) alignment and their applications to photonics are reviewed. The molecular alignment of LCs can be controlled by either the photochemical process or the photophysical process and we can change the birefringence as well as refractive index of the material by the modulation of the LC alignment. The photoresponsive LCs show very quick response to stimulus light: the response time is ∼200 ns. Furthermore, the extremely large refractive index modulation (Δ n=∼10 −1) can be also induced. The photoresponsive LCs, therefore, are potential materials for holographic recording and other photonic device.

Shrinkage- and refractive-index shift-corrected volume holograms for optical interconnects

The Bragg mismatching condition for volume holograms occurs because of the changes in the thickness and the refractive index of holographic recording materials during the recording and reconstruction procedures. We propose an improved compensation method to physically correct these effects in the fabrications of volume holograms for optical interconnects. In order to show the validity of this method, Slavich photographic plate VRP-M is used to fabricate optical interconnects. The correction of the Bragg diffraction angle shift of about 2.10°, which is induced by 6.14% film shrinkage and 0.06 refractive index shift, is successfully demonstrated with the surface-normal configuration. A shrinkage- and refractive-index shift-corrected volume hologram with 23% diffraction efficiency is experimentally confirmed. The methodology proposed is applicable to other phase media when the associated film shrinkage and refractive-index shift data are experimentally determined.

Two-Photon Photochromism of an Organic Material for Holographic Recording

We report the two-photon-induced photoisomerization of 3-[1-(1,2-dimethyl-1H-indol-3yl)-ethylidene]-4-isopropylidene-dihydrofuran-2,5-dione (1), a photochromic compound with Imax ) 385 nm, using 775-nm femtosecond pulsed laser irradiation. The resulting photoisomer had Imax ) 582 nm. The kinetic rate constant for the two-photon-induced electrocyclic isomerization reaction was measured at two different intensities (two different powers), showing a quadratic dependence with respect to the pump intensity. Results of pump-probe solution phase experiments and guest/host polymer thin film interferometric imaging studies are reported. A two-photon absorption molecular cross section U2 ) 10.3 10 -48 cm 4 ‚s/photon was measured using Z-scan, further supporting a two-photon-induced isomerization process. Two-photon-induced interferometric recording in a fulgide-containing polymer film was demonstrated.

New holographic recording material: bromothymol blue dye with rosin

Abstract The characterisation of a solution made up of bromothymol blue (BTB) combined with rosin and diluted in isopropyl alcohol, as a holographic recording material was carried out. This process was based on the recording of diffraction grating, under a range of recording parameters such as: BTB concentration, rosin concentration, a range of interference angles for grating generation, as well as a range of illumination wavelengths, and finally a study of the development process using a range of development times. The holographic gratings produced using this material show a high sensitivity to blue and blueish green illumination (λ=457, 476 and 488 nm), i.e. using an Argon Ion laser as well as a high-spatial resolution of the order of 1100 l/mm, thus demonstrating that it is feasible to obtain other HOEs using the proposed material.

Study of Effect of Bifunctional Crosslinking Agent in Polyvinylalcohol-Based Photopolymerizable Holographic Recording Material Using Angular Responses

Polyvinylalcohol-based holographic recording materials have important properties and the monomeric composition of such materials has been optimized in terms of the energetic sensitivity and diffraction efficiency. High sensitivity has been obtained by adding a crosslinking agent, and gratings with a diffraction efficiency near 70% with energetic exposures of 5 mJ/cm2 and a spatial frequency of 1000 lines/mm in photosensitive films 100-µm-thick have been obtained when N,N′-dihydroxiethylenebisacrylamide has been added. In this paper, we present the effects of intensity, thickness, and variation of the concentration of each the crosslinking agent by studying the angular responses of the diffraction gratings recorded.

New photopolymerizable holographic recording material based on polyvinylalcohol and 2-hydroxiethylmethacrylate (HEMA)

We have developed a new polyvinylalcohol-based photopolymeric holographic recording material. The recording is obtained by the copolymerization of acrylamide and 2-hydroxiethylmethacrylate (HEMA). Diffraction efficiencies near 70% are obtained with exposures of ≈65 mJ/cm2 in materials of 110-μm thickness. The addition of HEMA increases the thickness of the film, which results in improved storage capacity for holographic optical storage.

Transient volume holograms in polymethylmethacrylate

Abstract New transient volume holographic recording materials are described in this report. These consist of either coronene or 1,2;5,6-dibenzanthracene incorporated into polymethylmethacrylate. The largely amplitude, volume holograms formed as a result of triplet-state absorption have lifetimes of 6.4 and 0.9 s respectively and diffraction efficiencies close to the predicted values of ∼10 −4 . Production of permanent holograms has been prevented by careful control of the polymerization conditions to produce a matrix of sufficient rigidity to prevent reactions between the triplet states and the polymer. By using spectrally well separated write and read wavelengths, erasure of the holograms by the read beam is avoided.

Advances in Holographic Recording Materials

Advances in Holographic Recording Materials

Two dyes for holographic recording material: panchromatic ion pair from Rose Bengal and Methylene Blue

Abstract An ion pair (RBMB) isolated from Rose Bengal and Methylene Blue has been used as the photoinitiator in formulations of photopolymers tested as holographic recording materials in the form of dry films. Under irradiation with light of wavelength 633 or 514 nm, diffraction efficiencies of 65 and 35%, and sensitivities of 30 and 100mJcm−2 have been respectively reached, with a spatial resolution of ca. 1000 lines mm−1. These holographic responses are better than those reached under comparative conditions using a 1:1 physical mixture of the individual dyes. The influence of the light intensity on the photoinitiation of the polymerization process yielding the hologram has also been studied.

Two dyes for holographic recording material: Panchromatic ion pair from Rose Bengal and methylene blue

An ion pair (RBMB) isolated from Rose Bengal and Methylene Blue has been used as the photoinitiator in formulations of photopolymers tested as holographic recording materials in the form of dry films. Under irradiation with light of wavelength 633 or 514 nm, diffraction efficiencies of 65 and 35%, and sensitivities of 30 and 100mJcm−2 have been respectively reached, with a spatial resolution of ca. 1000 lines mm−1. These holographic responses are better than those reached under comparative conditions using a 1:1 physical mixture of the individual dyes. The influence of the light intensity on the photoinitiation of the polymerization process yielding the hologram has also been studied.

A new holographic recording material and its diffraction efficiency increase effect: the use of photoinduced surface deformation in azo-polymer film

Holographic recording characteristics using a photoinduced surface deformation in a side-chain type azo-polymer film were investigated. Corona charging at temperatures above the glass transition temperature increased the diffraction efficiency of the recorded hologram from 0.24% to about 30% and the relief depth from 20 to 350 nm.

Thickness variation of self-processing acrylamide-based photopolymer and reflection holography

There are many types of holographic recording material. The acrylamide-based recording material examined here has one significant advantage: it is self-processing. This simplifies the recording process and enables holographic interferometry to be carried out without the need for complex realignment procedures. However, the effect that the polymerization process has on the grating thickness must be examined. This question is fundamental to the material's use in holographic optical elements, as thickness variations affect the replay conditions of the pro- duced elements. This paper presents a study of this thickness variation and reports for the first time the production of reflection holographic grat- ings in this material. © 2001 Society of Photo-Optical Instrumentation Engineers.

Photopolymer holographic recording material

Photopolymers are promising materials for use in holography. They have many advantages, such as ease of preparation, and are capable of efficiencies of up to 100%. A disadvantage of these materials is their inability to record high spatial frequency gratings when compared to other materials such as dichromated gelatin and silver halide photographic emulsion. Until recently, the drop off at high spatial frequencies of the material response was not predicted by any of the diffusion based models available. It has recently been proposed that this effect is due to polymer chains growing away from their initiation point and causing a smeared profile to be recorded. This is termed a non-local material response. Simple analytic expressions have been derived using this model and fits to experimental data have allowed values to be estimated for material parameters such as the diffusion coefficient of monomer, the ratio of polymerisation rate to diffusion rate and the distance that the polymer chains spread during holographic recording. The model predicts that the spatial frequency response might be improved by decreasing the mean polymer chain lengths and/or by increasing the mobility of the molecules used in the material. The experimental work carried out to investigate these predictions is reported here. This work involved (a) the changing of the molecular weights of chemical components within the material (dyes and binders) and (b) the addition of a chemical retarder in order to shorten the polymer chains, thereby decreasing the extent of the non-local effect. Although no significant improvement in spatial frequency response was observed the model appears to offer an improved understanding of the operation of the material.

Improvement of holographic recording material using aerosol sealant

Self-processing photopolymer based materials offer significant practical advantages when recording holographic optical elements, HOEs. However, such materials, e.g. acrylamide based photopolymer, are seriously effected by ambient environmental conditions, in particular by fluctuations in humidity. Such sensitivity can result in a short active material shelf-life prior to recording, material variations during the recording and self-processing stages and HOE deterioration following recording. In this paper we examine the use of an aerosol sealant (varnish) to `insulate' the photopolymer holographic recording material from the environment. Application of the sealant is found to produce some deterioration in the optical quality of the resulting HOEs. However, it is also shown to produce an increased lifetime of the active material (pre-recording), an increase in the diffraction efficiency from the resulting diffraction gratings recorded and improved HOE shelf-life.

Obtention of photosensitive films as holographic recording materials

En este articulo se presenta, en primer lugar, el procedimiento de obtencion y depositado de peliculas fotosensibles secas utilizadas como material de registro holografico, comparando el espesor y uniformidad de las placas obtenidas con dos metodos de depositado distinto, con un depositador manual y con un depositador automatico. En segundo lugar se analiza la influencia del espesor en el comportamiento del material como material de registro holografico.

Dynamical behaviour of the optical properties of photopolymers and the lorentz-Lorenz formula

Photochemical variations of the refraction index of dielectrics are explored using the Lorentz-Lorenz formula. The scope of this analysis is restricted to photoinitated chemical reactions in the optical range that originates small differences in the refraction index, assuming that the dielectric constitutes an approximately constant background. These types of systems are relevant when considering the optical macroscopic response of holographic recording materials. Relations arising from a photopolymer are analysed in detail.