Recording Of Phase Holograms Research Articles

Water Resistant Cellulose Acetate Based Photopolymer for Recording of Volume Phase Holograms

The development of environmentally robust photosensitive materials for holographic recording is crucial for applications such as outdoor LED light redirection, holographic displays and holographic sensors. Despite the progress in holographic recording materials development, their sensitivity to humidity remains a challenge and protection from the environment is required. One approach to solving this challenge is to select substrate such as cellulose acetate, which is water resistant. This work reports the development of a cellulose-based photopolymer with sensitivity of 3.5 cm2/mJ and refractive index modulation of 2.5 × 10−3 achieved in the transmission mode of recording. The suitability for holographic recording was demonstrated by recording gratings with the spatial frequency of 800 linepairs/mm. The intensity dependence of the diffraction efficiency of gratings recorded in 70 μm thick layers was studied and it was observed that the optimum recording intensity was 10 mW/cm2. The robustness of the structures was studied after immersing the layer in water for one hour. It was observed that the diffraction efficiency and the surface characteristics measured before and after exposure to water remain unchanged. Finally, the surface hardness was characterized and was shown to be comparable to that of glass and significantly higher than the one of PVA-based acrylamide photopolymer.

Prospects for Practical Applications of a Discharge Chemical HF Laser as a Coherent Source for IR Holography

Preliminary experimental results on recording of phase and amplitude holograms using the radiation of electric-discharge HF lasers are presented, and prospects for applications of such lasers in diagnostics of various objects are discussed. It is shown that lasers with homogeneous working medium may generate coherent radiation with a coherence length of greater than 6 m in the absence of mode selection. Methods for control of spatial distribution of electron concentration in excimer and discharge chemical HF (DF) lasers and distributions of the main combustible components are considered. Deposition of holographic identification marks on artworks is studied.

Specific features of electrical conductivity of LiTaO3 and LiNbO3 crystals in the temperature range of 290–450 K

The electrical conductivity of single crystals of lithium tantalate and lithium niobate of the congruent composition not subjected to special thermochemical treatments has been investigated in the temperature range of 290–450 K. It has been shown that the charge transfer mechanisms and carrier types in these crystals are identical in the temperature range under study. The presence of mobility anisotropy of conduction electrons has been revealed and its influence on the recording and storage of optical phase holograms in these crystals has been established.

Gradient of refractive index (GRIN) effect in photo-thermo-refractive glass

Photo-thermo-refractive (PTR) glass is a photosensitive multicomponent silicate glass containing photosensitive agents such as cerium and silver. Photoinduced crystalline phase precipitation results in refractive index variations in exposed areas of PTR glass, which has been successfully used for phase hologram recording. Photosensitivity being the result of the partial absorption of the exposing radiation by cerium ions, it results in a gradient of refractive index (GRIN) along the exposure beam propagation. This GRIN is a parasitic effect that deteriorates the parameters of some types of volume Bragg gratings because of the beam deflection they produce. In this paper, the evolution of GRIN is investigated as a function of the dosage of UV exposure and the thermal treatment duration. We show that GRIN is a deterministic process that can be easily modeled and predicted using basic optics and glass science equations.

Generation and bleaching of intrinsic color centers in photo-thermo-refractive glass matrix

Photo-thermo-refractive (PTR) glass is a photosensitive multicomponent silicate glass that imparts refractive index change after exposure to ionizing radiation and thermal treatment. The origin of this photosensitivity is explained by thermal precipitation of sodium fluoride crystals controlled by atomic silver nucleation centers. These centers are produced by photo-reduction of silver ions resulted from photoionization (photo-oxidizing) of cerium ions. This feature of PTR glass is successfully used for high efficiency phase hologram recording. However, the mechanism of electric charge exchange (transfer) between these ions is not known and the role of intrinsic electron and hole centers was not studied. To elucidate this problem, pure PTR glass matrix with no dopants was prepared and the subsequent absorption spectra of color centers were studied after excitation of the intrinsic absorption edge of glass matrix. Color centers were bleached by thermal treatment and by optical excitation of induced absorption bands. The analysis of the structure of absorption spectra at different stages of coloration and bleaching led to the deconvolution of complex spectra to Gaussian components. Based on this analysis and comparison with simple silicate glasses, induced absorption bands were assigned to different intrinsic electron and hole centers. Interconversion of different centers is also studied.

Evolution of Absorption Spectra in the Process of Nucleation in Photo-Thermo-Refractive Glass

Photo-thermo-refractive (PTR) glass belongs to a class of photosensitive multicomponent silicate glasses which demonstrate photo-thermo-induced precipitation of a crystalline phase. Photo-induced crystallization of sodium fluoride results in refractive index variations in exposed areas of PTR glass which was successfully applied for phase hologram recording. However, even if this glass is widely used for advanced optical applications such as the stabilization of laser diodes or spectral beam combining, the detailed mechanism of its photosensitivity is not well known. We present in this paper an analysis of the evolution of the absorption spectra of UVexposed PTR glass at the early stages of the thermal treatment (nucleation). Absorption spectra were measured on samples nucleated at constant temperature for different periods. Analysis of the structure of these spectra shows that the optimum of the nucleation process is associated with the appearance of a new absorption band in visible range that disappears when the crystal growth process starts. Analogous study was performed during the nucleation process. High temperature spectroscopic measurements were performed during the thermal treatment. It was found that absorption spectra evolve with a change of temperature, i.e. the band structure of these spectra is different whether or not the temperature is decreased below a temperature of ~400°C. We associate this process with the change of phase of the silver bromide nuclei (liquid/solid) that appears during the cooling or heating processes.

Fabrication and characterization of poly(methyl methacrylate) photopolymer doped with 9,10-phenanthrenequinone (PQ) based derivatives for volume holographic data storage

We present our studies on the photopolymer of poly(methyl methacrylate) (PMMA) doped with 9,10-phenanthrenequinone based derivatives for volume holographic storage. By introducing different functional groups on the side-chain of 9,10-phenanthrenequinone molecule, the holographic characteristics of the material can be modified. The photoreaction involved with the holographic recording in the samples was investigated by measuring UV–Vis absorption spectrum and mass spectrum. The experimental results show that the similar behaviors were exhibited in these photopolymers. It is found that phase hologram recording in our PQ derivatives doped PMMA photopolymer involves a structure change of the quinone based molecule, which induces a strong change of the refractive index. Experimental characterizations on holographic data storage, including material sensitivity, dynamic range ( M#) and bit-error-rate have been performed. We found that, by selecting appropriate functional groups, an improvement in sensitivity and M# for holographic data storage can be achieved.

Anomalies in the pyroelectric properties of LiNbO3 crystals of the congruent composition

A number of anomalies are revealed in the temperature dependence of the primary pyroelectric coefficient for single-domain crystals of lithium niobate LiNbO3 in the temperature range 310–330 K. It is shown that these anomalies are associated with the transformation of the domain structure of the lithium niobate crystals. The problem regarding the correct performance of the pyroelectric measurements and the possible influence of the observed effects on the optical properties of lithium niobate crystals and on the recording of optical phase holograms are discussed.

PROJECTION OF HOLOGRAMS FROM PHOTOREFRACTIVE OASLMs

Liquid crystals doped with fullerenes and carbon nanotubes (CNTs) act as good optical nonlinear materials. We have used these materials to build optically-addressed spatial light modulators (OASLMs). The devices comprise a single layer of doped liquid crystal acting as an active layer. Undoped LC devices with surfaces coated with fullerenes are also studied. Such OASLMs allow recording of phase holograms, and we record by imaging pre-calculated pre-recorded holograms. Writing is performed at normal incidence and reading at 45° oblique incidence. Both transmission and reflection modes of operation are used. Experimental results as well as comparison with commercially available OASLMs are presented.

Comparison of the effects of two bleaching agents on the recording of phase holograms in silver halide emulsions

Optical densities before bleaching and final Lin-curves of plane-wave phase holograms recorded in Agfa-Gevaert 8E75HD emulsions were determined for combinations of the AAC developer with a solvent bleach (R-9) and a (fixation-free) rehalogenating bleach (R-10). To characterize the processing, the square root of the diffraction efficiency of the processed holograms was related to the amplitude of the optical density modulation obtained at the development step. Sensitivity, linearity and dynamic range of the processes could thereby be compared directly.

Hologram formation in dichromated gelatin: an approach based on light scattering from nanoparticles

Dichromated gelatin is one of the best materials for phase-hologram recording. Several competing hypotheses for the nature of the photoinduced response in DCG have been discussed in the literature. Of particular interest is the assumption that processing of the latent image leads to the formation of voids in the gelatin matrix. Here, we analyze the DCG hologram performance in terms of the theory of light scattering from these voids – ellipsoids with dimensions of 10–40 nm. Mathematical simulations of the reflection spectra give a plausible quantitative explanation of many experimental facts related to DCG holograms.

Effect of reflections on phase hologram recording in amorphous As-S-Se films

Experimental and theoretical studies of phase hologram recording in amorphous As-S-Se films with slightly wedge-shaped thickness profile are presented. It is shown that Fabry-Perot resonator effect caused by the interference of multiply reflected light beams inside the sample strongly changes the values of diffraction efficiency and its growth rate as well as the exposure time dependences of diffraction efficiency and transmissivity making them site-dependent and sample-dependent. Absorptivity and recording light intensity inside the sample are also significantly changed. The obtained results can be used to explain the holographic and optical experiments also in other materials with Fabry-Perot resonator effect such as other transparent thin films and photorefractive crystals.

Recording of thin phase holograms in polymer-dispersed liquid-crystal composites based on fullerene-containing π-conjugated organic systems

The recording of thin phase holograms in promising fullerene-containing, polymer-dispersed liquid-crystal composites based on 2-cyclooctylamino-5-nitropyridine and N-(4-nitrophenyl)-(L)-prolinol using picosecond laser pulses is studied for the first time. The anisotropy of the refractive index substantially increases after laser irradiation and exceeds by a factor of five this anisotropy for liquid-crystal cells containing dyes. The results of our studies suggest that the fullerene-containing, polymer-dispersed liquid-crystal systems can be used as passive media for reversible data recording.

“Hidden” recording of phase holograms with self-amplification in a polymer with photoinduced diffusion

The possibility of minimizing the diffraction efficiency of a volume phase holographic grating while recording in a medium with diffusion self-amplification is considered. The recording process is modeled to demonstrate that the diffraction efficiency can be varied from 0.02 to 0.003 (50–250 gain). The results of the analysis are confirmed by the experimental data.

Ferroelectric domain gratings and Barkhausen spikes in potassium lithium tantalate niobate

The observation of Barkhausen current spikes during the recording of volume phase holograms in potassium lithium tantalate niobate is reported on. These spikes are due to the ferroelectric domain reversal induced by photorefractive space charge fields. Both “small” (1 nA) and “large” (100 nA) spikes are observed, which correspond to micro and macro domain reversal, respectively. The diffraction efficiency can change as much as 50% during a single macrodomain switching.

KINETICS OF DYNAMIC HOLOGRAM RECORDING IN POLYMER FILMS WITH IMMOBILIZED BACTERIORHODOPSIN

Abstract— Polymer films with immobilized photosensitive membrane protein, bacteriorhodopsin (BR), were prepared and investigated. A sensitive holographic interferometer with phase modulated optical beams was used for investigation of kinetics of dynamic hologram recording in BR polymer films. It was found that phase hologram formation consisted of two quasi-exponential stages demonstrating existence of a diffusive process in obtained films. It was shown that the kinetics of a phase hologram recording by high intensity beams do not correlate with the exponential law. The applicability of BR polymer films as reversible photorefractive materials for dynamic holography and real-time interferometry was discussed.

Two-level model of recording and reading of volume phase holograms in photorefractive crystals of BSO-type

A two-level model of optical transitions in crystals of BSO-type has been proposed for the effect of readout beam on the dynamic holographic grating to be taken into account, and an expression for diffraction efficiency representing the generalized formula by Vinetskii and coworkers [1–3] has been obtained.

Noninterferometric fabrication of computer-generated phase holograms on silver halide photographic emulsion

The potential of silver halide emulsion as a low-cost material for noninterferometric recording of computer-generated phase holograms is evaluated by contact-printing binary-amplitude masks on this material. This process is found to result in a nonbinary surface-relief profile with appreciable overshoot in the vicinity of the intended phase jumps. Interestingly, the refractive-index modulation profile compensates for this effect, resulting in a nearly binary phase delay profile. Residual absorption in the emulsion and pattern transfer errors, most noticeable within small features, are found to limit the array size that can be achieved with a given period. The feasibility of the application of silver halide emulsion in recording holograms with a continuous profile is discussed.

Bragg-effect grating couplers integrated in multicomponent polymeric waveguides

A new reactive multicomponent polymeric system is presented for the real-time optical recording of volume phase holograms integrated in waveguiding thin films. Efficient Bragg-effect grating couplers are produced holographically. In a multimodeplanar waveguide, the input coupling efficiency reaches 62% for an incident 633-nm He-Ne laser beam. Almost 96% of the mode power is emitted by a second coupler into one single-output beam.

Photoinduced light scattering in crystals with a nonlocal response

A theory of Rayleigh light scattering is developed for photorefractive media of the strontium barium niobate (SBN) type with a diffusion mechanism of formation of optical inhomogeneities. The photoinduced increase in the scattering intensity is considered to be the result of spontaneous recording of noise phase holograms in an inhomogeneous crystal. The angular structure and the time dependence of this scattering intensity are determined. It is shown that as a result of holographic effects the scattering indicatrix may be essentially asymmetric. Theoretical calculations made for an SBN crystal show good agreement with the experimental results.