Holographic Sensitivity Research Articles

Влияние поля коронного разряда на формирование голографических дифракционных решеток в пленках As-=SUB=-40-=/SUB=-S-=SUB=-60-x-=/SUB=-Se-=SUB=-x-=/SUB=-

The influence of the corona discharge on the holographic recording and the subsequence chemical etching of the recording holographic gratings in the Cr/As40S60-xSex thin film structures was investigated. It was established that applied of the positive corona discharge leads to the increase of the holographic sensitivity during the recording in the As-S-Se films, as well as to the amplification of the diffraction efficiency of the recording gratings and of the relief-phase diffractive gratings obtaining in the result of the consecutive chemical etching. Among the investigated films of the As40S60-xSex system, the best results on the application of the Argon laser irradiation (=488 nm) was obtaining for the composition As40S39Se21. Applied of the corona discharge bring to the increase of the holographic sensitivity more than up two order, and of the diffraction efficiency about three order in the respect of the of the ordinary recording. Reciprocally was reached a amplification of the diffraction efficiency of the relief diffraction gratings formed in the result of the sequent chemical etching up to 30 %.

Influence of the corona discharge on the formation of the diffractive holographic gratings in the As-=SUB=-40-=/SUB=-S-=SUB=-60-x-=/SUB=-Se-=SUB=-x-=/SUB=- films

The influence of the corona discharge on the holographic recording and the subsequence chemical etching of the recording holographic gratings in the Cr/As40S60-xSex thin film structures was investigated. It was established that applied of the positive corona discharge leads to the increase of the holographic sensitivity during the recording in the As-S-Se films, as well as to the amplification of the diffraction efficiency of the recording gratings and of the relief-phase diffractive gratings obtaining in the result of the consecutive chemical etching. Among the investigated films of the As40S60-xSex system, the best results on the application of the Argon laser irradiation (488 nm) was obtaining for the composition As40S39Se21. Applied of the corona discharge bring to the increase of the holographic sensitivity more than up two order, and of the diffraction efficiency about three order in the respect of the of the ordinary recording. Reciprocally was reached a amplification of the diffraction efficiency of the relief diffraction gratings formed in the result of the sequent chemical etching up to 30%. Keywords: chalcogenide vitreous semiconductors, holographic diffractive grating, corona discharge, diffraction efficiency, selective etching.

Effect of Corona Discharge on the Optical Properties of Thin-Film Cu–As2Se3 Structures

The effect that corona discharge has on holographic recording of diffraction gratings in a thin-film Cu−As2Se3 structure deposited on glass by thermal vacuum evaporation is studied. The use of negative corona discharge during holographic recording enhances the holographic sensitivity of the Cu−As2Se3 structure and the diffraction efficiency of inscribed gratings. Irradiation of the Cu−As2Se3 structure with actinic light results in photodarkening in the spectral region in which the structure exhibits a strongly absorption, while the region characterized by a weaker absorption becomes more transparent. The effect of photoinduced transparency is enhanced if samples are treated using positive corona discharge and with negative corona discharge the effect is weakened. The experimental results are explained qualitatively, assuming the diffusion of Cu+ ions into the As2Se3 layer.

Влияние коронного разряда на оптические свойства тонкопленочных структур Cu-As-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=-

Effect of corona discharge on holographic recording of diffraction gratings in Cu-As2Se3 thin film structure was studied. Thin film structures of Cu-As2Se3 were prepared on glass substrates by sequential deposition of Cu and As2Se3 layers using vacuum thermal evaporation technique. Applying of negative corona discharge during recording procedure caused an enhancing both of the holographic sensitivity and diffraction efficiency of the grating. Exposure to actinic light illumination resulted in photodarkening effect in Cu-As2Se3 thin film structure in the spectrum region of strong absorption. At the same time the fotoinduced bleaching of Cu-As2Se3 film structure in the spectrum region of weak absorption was observed. Negative corona discharge applied during the light exposure enhanced the bleaching, while positive corona discharge caused its weakening. The photoinduced diffusion of Cu+ ions into As2Se3 film was considered to explain qualitatively the experimental results.

Holographic response characteristics influenced by an absorptive diffusion polymerization model in bulk TI/PMMAs.

Dynamic formation of a volume holographic grating is mainly caused by the diffusion polymerization of a photoinitiator in TI/poly-(methyl methacrylates) (PMMAs). Here, we consider the time-dependent absorption coefficient in this material to establish an absorption modulated diffusion polymerization model. An experimental and theoretical investigation in TI/PMMAs with different sample thicknesses (1-3 mm) is presented. It is indicated that the thickness can regulate the holographic sensitivity and constancy in TI/PMMAs. Furthermore, we also examined the dark diffusion process, multiplexed gratings recording, pre-exposure holographic enhancement, and long-term full exposure in TI/PMMAs with different thicknesses to analyze their holographic sensitivity and constancy. It is predicted that, in general, the absorption characteristics in TI/PMMA can be further affected by changing its thickness, thus it is able to satisfy different requirements in high-density holographic memories.

Effect of corona discharge on formation of holographic diffraction gratings in the Cu–As2Se3 thin-film structure

Application of negative corona discharge in the course of recording leads to an increase in the holographic sensitivity of the Cu–As2Se3 structure and diffraction efficiency of the recorded holographic gratings and the relief gratings fabricated with the aid of chemical etching. Positive corona discharge impedes the recording of holographic gratings in the Cu–As2Se3 structure. The Cu–As2Se3 structure exhibits the properties of a negative photoresist under irradiation in the presence of the negative corona discharge. In addition, the dissolution selectivity substantially increases due to the corona discharge.

Electromagnetic holographic sensitivity field of two-phase flow in horizontal wells

Electromagnetic holographic data are characterized by two modes, suggesting that image reconstruction requires a dual-mode sensitivity field as well. We analyze an electromagnetic holographic field based on tomography theory and Radon inverse transform to derive the expression of the electromagnetic holographic sensitivity field (EMHSF). Then, we apply the EMHSF calculated by using finite-element methods to flow simulations and holographic imaging. The results suggest that the EMHSF based on the partial derivative of radius of the complex electric potential φ is closely linked to the Radon inverse transform and encompasses the sensitivities of the amplitude and phase data. The flow images obtained with inversion using EMHSF better agree with the actual flow patterns. The EMHSF overcomes the limitations of traditional single-mode sensitivity fields.

Influence of charging chalcogenide glassy semiconductors in a corona discharge on the formation of superimposed holographic diffraction gratings

Optical recording of superimposed holographic gratings in a corona discharge initiated in a Ni-As2S3 structure is studied. It is shown that a corona discharge used for recording holographic gratings in this structure improves its holographic sensitivity and the diffraction efficiency of recorded gratings by several times. It is found that when two superimposed gratings are recorded in a corona discharge, a surface relief due to chemical etching is more uniform and the modulation depth of its thickness is larger.

A study of the effect of a corona discharge on recording of holographic diffraction gratings in the Cu-As2S3 structure

Improvement of the optical recording process in the Cu-As2S3 structure in the whole visible band was observed when the structure is simultaneously exposed and charged in the field of a negative corona discharge as compared to the standard direct recording in the above-mentioned structure. It was shown that using the negative corona discharge for recording in these structures allows the holographic sensitivity and diffraction efficiency of the recorded holographic diffraction gratings to be increased several-fold compared to gratings obtained by the standard approach. The results are discussed using the known photoelectrical model.

Information media based on electron donor oligomers with different structures.

Information properties of recording media for photothermoplastic techniques were investigated. The films consisted of oligomer composites based on carbazole containing co-oligomers of linear and radial structures with branching centers on silicon and germanium atoms. It was ascertained that the media based on the radial oligomers possessed high holographic sensitivity because of the high plasticity and its ability to accumulate volume electric charge during the exposure. Examples of practical applications of the investigated recording media are presented.

Peculiarities of holographic media based on electron donor oligomers of linear and radial structures

The information properties of holographic recording media for photothermoplastic recording with films of oligomer composites based on carbazolyl-containing linear and star co-oligomers with branching centers on silicon and germanium atoms have been studied. The media based on the star oligomers possess higher holographic sensitivity due to greater plasticity and ability to accumulate space electrical charge during exposure. The buildup of space electrical charge results from the capture of photogenerated holes by energy traps created by dimers formed from terminal carbazolyl groups, whose amount is larger in macromolecules of radial oligomers than in linear oligomers.

Sensitization of Photosemiconducting Properties of Holographic Recording Media Based on Glycidylcarbazole Cooligomers by Organic Dyes

Photophysical and information properties of the holographic recording media (HRM) based on films of ferrocenyl-containing siloxane oligomer, glycidylcarbazole-butylglycidylic ether cooligomer, ferrocenemethylated oligoglycidylcarbazole, and cooligomer of o-carboxybenzoilferrocene glycidylic ether doped with squarilic dye and(or) with merocyanine dye based on ferrocene and tetranitrofluorene are investigated. It is found that the holographic sensitivity is absent for the media based on ferrocenyl-containing siloxane oligomer, and that the holographic sensitivity is present for the films based on glycidylcarbazole. It has been found that the holographic sensitivity and the photoconductivity of the media based on glycidylcarbazole cooligomers increases with the ferrocene content. This effect has been explained by the influence of iron ions on the rate of singlet–triplet conversion in photogenerated pairs of charges.

Influence of the sensitizer reduction potential on the sensitivity of photorefractive polymer composites

We report on a series of near infrared (NIR)-sensitive photorefractive polymer composites (PPCs) based on the hole-conducting polymer PF6-TPD, which are sensitized by soluble fullerene-derivatives as electron-accepting agents. We demonstrate a direct correlation between the electron accepting capability of the sensitizer and the holographic response time. The holographic recording speed is found to improve by one order of magnitude when lowering the reduction potential of the sensitizer by approx. 400 mV, while all other physical parameters of the materials remain essentially identical. Furthermore, the lifetime of the mobile charge carriers is found to correlate linearly with the reduction potential, thus indicating a decrease in recombination rates for stronger accepting capability of the sensitizer. Finally, we found that pre-illumination enhanced the holographic sensitivity. The effect is found to be most pronounced for the strongest acceptor due to reduced recombination of the preformed carriers. Overall, the PPCs reported here feature the currently highest sensitivity in the NIR spectral region.

Holographic Recording with Polymer Nanocomposites Containing Silver Nanoparticles Photogenerated in Situ by the Interference Pattern

A process allowing in situ photochemically assisted synthesis of silver nanoparticles (NPs) in a polymerizable acrylic formulation was developed and the photopolymerization of this formulation was studied. It has been found that the presence of NPs does not perturb the polymerization process in the least, making it possible to fabricate metal/polymer nanocomposites by a one-step, one-pot photochemical process. The size distribution of NPs was very narrow and their size could be controlled by the chemical parameters of the reactive formulation. This system was used to record holographic gratings, and it was observed that both the holographic sensitivity and the diffraction efficiency at maximum were significantly improved in the presence of particles. Moreover, AFM analysis revealed a clear-cut segregation of photochemically generated NPs between dark and bright regions of the incident pattern, thus demonstrating the possibility to manipulate nascent particles with light gradients.

Photosemiconducting properties of holographic media based on ferrocenyl-containing cooligomers of glycidyl carbazole with these oligomers sensitized by organic dye

Spectral, photosemiconducting, and information properties of holographic recording media with films of glycidyl carbazole-butyl glycidyl ether cooligomer, methylated ferrocenyl oligoglycidyl carbazole, and o-carboxybenzoyl ferrocene glycidyl ether cooligomer with squaryl dye additives were studied. An increase in the holographic sensitivity and photoconductivity of recording media with ferrocenyl-containing cooligomer films in comparison with media based on a glycidyl carbazole cooligomer was found. This phenomenon was attributed to the effect of iron ions on the singlet-triplet conversion rate in photogenerated charge pairs, which was validated by analyzing the dependence of the photocurrent on the external magnetic field. A phenomenological model of the effect of ferrocene on the photoconductivity of studied films was proposed.

Two-photon induced photorefraction in undoped lithium tantalate crystals with different compositions

Two-photon interband photorefraction in undoped lithium tantalate crystals with composition ranging from 47.95 to 49.6 mol% of lithium oxide was demonstrated at the wavelength of 532 nm. The photorefractive properties were examined with holographic method. Two-photon holograms were recorded with high holographic sensitivity, large refractive index change, and fast hologram writing time. Permanent changes of the refractive index have been obtained. These holograms can be read nondestructively at the wavelength of 660 nm using heterodyne method. Holographic characteristics strongly depend on composition.

Charging of glassy chalcogenide semiconductors in corona discharge and its effect on holographic grating formation

Recording of optical holographic gratings based on photostructural transformations in thin (≈ 1 μm) As2S3 and As2S3 semiconductor layers in the presence and absence of a corona discharge and also chemical etching of these gratings are studied. Initiation of a corona at the stage of interference grating recording is shown to improve the exposure contrast of metal-glassy chalcogenide semiconductor thin-film structures. The holographic sensitivity, diffraction efficiency, dynamic range, and contrast are also improved severalfold. When phase relief gratings formed in these layers are selectively etched in a chemical etchant in the presence of a corona, their profile becomes more regular and deeper by 25–30% and the diffraction efficiency increases by 30–50%.

Sensitivity of volume holographic media

This paper discusses an informational criterion for determining the input energy needed for recording in volume holographic media. A definition of the informational holographic sensitivity is given. The threshold informational holographic sensitivity in the case of binary and half-tone recording is defined. The connection of the informational sensitivity with the dynamic range of the medium in a volume medium is taken into account. A comparison is made of the informational holographic and ordinary sensitivities for certain thin and volume media used in holography.

Croconium dye as a sensitizer of photothermoplastic holographic media for the near-IR region

This paper discusses the spectral and photoconductive properties of films based on a co-oligomer of glycidylcarbazole with additives of croconium dye in comparison with similar films with squarylium, merocyanine, and cationic polymethine dyes. It is concluded that croconium dye, like merocyanine dye, belongs to the electron-nonsymmetric organic dyes. The possibility of using croconines as sensitizers of photothermoplastic holographic recording media for the near-IR region is demonstrated for the first time. The lower holographic sensitivity of recording media with croconium dye by comparison with squarylium and merocyanine dyes is associated with the presence of deep traps for charge carriers, which are formed by the molecules of an intraionic dye and are liberated when heated in the process of development of the holograms.

Two-photon recording of microholograms in undoped lithium tantalate

Two-photon recording of microholograms was demonstrated in undoped congruent lithium tantalate crystal with high holographic sensitivity, large refractive index change, and fast hologram writing time. Nonvolatile heterodyne readout was carried out at a wavelength of 660 nm. Recording of a 3 x 3 x 3 matrix of microholograms was realized and it showed the cross-talk effect was negligibly small.