Photorefractive response and real-time holographic application of a poly(4-(diphenylamino)benzyl acrylate)-based composite

Photorefractivity and photocurrent dynamics of triphenylamine-based polymer composites

The photorefractive properties of triphenylamine polymer-based composites with various composition ratios were investigated via optical diffraction, response time, asymmetric energy transfer, and transient photocurrent. The composite consisted of a photoconductive polymer of poly((4-diphenylamino)benzyl acrylate), a photoconductive plasticizer of (4-diphenylamino)phenyl)methanol, a sensitizer of [6,6]-phenyl-C61-butyric acid methyl ester, and a nonlinear optical dye of (4-(azepan-1-yl)-benzylidene)malononitrile. The photorefractive properties and related quantities were dependent on the composition, which was related to the glass transition temperature of the photorefractive polymers. The quantum efficiency (QE) of photocarrier generation was evaluated from the initial slope of the transient photocurrent. Transient photocurrents were measured and showed two unique peaks: one in the range of 10-4 to 10-3 s and the other in the range of 10-1 to 1 s. The transient photocurrents was well simulated (or reproduced) by the expanded two-trapping site model with two kinds of photocarrier generation and recombination processes and two different trapping sites. The obtained photorefractive quantity of trap density was significantly related to the photoconductive parameters of QE.

3D optical illusion as visualisation tools in spatial planning and development

Spatial planning and development use various visualisation methods. Technological advancements in visualisation techniques have allowed imaging to shift from 2 to 3D dimensions. 3D optical illusion, which converts information recorded in the digital form into a three-dimensional presentation, can be a new tool for presenting spatial development solutions. Since a optical illusion is a direct spatial presentation, it requires neither specialist preparation nor spatial imagination. For this reason, it can become an effective means of visual communication with the public in the area of spatial planning and development. This article shows an example of the imaging of a model element of spatial development (a building) using the 3D illusion technique. Collected opinions of the test group of viewers confirm the usefulness of this tool. The presented 3D visualisation effect evoked positive reactions among the viewers. The use of the hologram technique in spatial planning and development appears to be justified and is an interesting research trend.

Photorefractive Response Enhancement in Poly(triarylamine)-Based Polymer Composites by a Second Electron Trap Chromophore

Photorefractive (PR) performances are affected by the components of the photoconductor, sensitizer, nonlinear optical dye, and plasticizer. A photoconductor with high hole mobility promises a faster response time, whereas it induces higher photoconductivity, which leads to easy dielectric breakdown. Adding a second electron trap is effective in controlling photoconductivity. In this study, the role of a second electron trap 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (TmPyPB) was investigated in a PR composite consisting of a photoconductor of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] with a high hole mobility, a nonlinear optical chromophore of piperidinodicyanostyrene, a plasticizer of (2,4,6-trimethylphenyl)diphenylamine, and a sensitizer of [6,6]-phenyl C₆₁ butyric acid-methyl ester. The minimum time response with the maximum optical diffraction efficiency and sensitivity was measured at a 1 wt % content of TmPyPB. These results were consistent with the number of charge carriers trapped per unit volume and per unit time N _c (cm^-3 s^-1), which is defined as the ratio between the initial trap density T _i (cm^-3) and response time τ (s), at a 1 wt % content of TmPyPB. A faster response time of 149 μs, optical diffraction of 24.1% (external diffraction of 4.8%), and a sensitivity of 2746 cm² J^-1 were measured at 50 V μm^-1 for the sample with 1 wt % TmPyPB. High loading of 5 wt % TmPyPB led to a large decrease in photoconductivity and effectively suppressed the dielectric breakdown under a stronger electric field, whereas a slower response time with lower diffraction efficiency was observed for optical diffraction.

Review of Organic Photorefractive Materials and Their Use for Updateable 3D Display

Photorefractive materials are capable of reversibly changing their index of refraction upon illumination. That property allows them to dynamically record holograms, which is a key function for developing an updateable holographic 3D display. The transition from inorganic photorefractive crystals to organic polymers meant that large display screens could be made. However, one essential figure of merit that needed to be worked out first was the sensitivity of the material that enables to record bright images in a short amount of time. In this review article, we describe how polymer engineering was able to overcome the problem of the material sensitivity. We highlight the importance of understanding the energy levels of the different species in order to optimize the efficiency and recording speed. We then discuss different photorefractive compounds and the reason for their particular figures of merit. Finally, we consider the technical choices taken to obtain an updateable 3D display using photorefractive polymer. By leveraging the unique properties of this holographic recording material, full color holograms were demonstrated, as well as refreshing rate of 100 hogels/second.

Enhancement of Photorefraction in Vanadium-Doped Lithium Niobate through Iron and Zirconium Co-Doping

A series of mono-, double-, and tri-doped LiNbO3 crystals with vanadium were grown by Czochralski method, and their photorefractive properties were investigated. The response time for 0.1 mol% vanadium, 4.0 mol% zirconium, and 0.03 wt.% iron co-doped lithium niobate crystal at 488 nm was shortened to 0.53 s, which is three orders of magnitude shorter than the mono-iron-doped lithium niobate, with a maintained high diffraction efficiency of 57% and an excellent sensitivity of 9.2 cm/J. The Ultraviolet-visible (UV-Vis) and OH- absorption spectra were studied for all crystals tested. The defect structure is discussed, and a defect energy level diagram is proposed. The results show that vanadium, zirconium, and iron co-doped lithium niobate crystals with fast response and a moderately large diffraction efficiency can become another good candidate material for 3D-holographic storage and dynamic holography applications.

The Island CGH, a new coding scheme: concept and demonstration

Computer generated holograms (CGHs) are powerful optical elements used in many fields, such as wavefront shaping, quality testing of complex optics, and anti-counterfeiting devices. The Lee algorithm is the most used to generate binary amplitude Fourier holograms. Grayscale CGHs are known to give a higher reconstruction quality than binary holograms, but they usually require a cumbersome production process. A very simple and straightforward method of manufacturing rewritable grayscale CGHs is proposed here by taking advantage of two key components: a digital micro-mirror device (DMDs) and a photochromic plate. An innovative algorithm, named Island algorithm, able to generate grayscale amplitude Fourier CGHs, is reported and compared with the standard Lee approach, based on 9 levels. A crucial advantage lies on the fact that the increase or decrease of the quantification does not affect the spatial resolution. In other words, the new coding leads to a higher spatial resolution (for a given CGH size) and a reconstructed image with an order of magnitude higher contrast with respect to the classical Lee-coded hologram. In order to show the huge potential of our approach, a 201 level Island hologram is designed, produced and reconstructed, pushing the contrast to values higher than10⁴. These results reveal the potential of our process as well as our algorithm for generating programmable grayscale CGHs.

Organic Optoelectronic Materials: Mechanisms and Applications

Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjugated polymers are considered, and their applications in organic solar cells, photodetectors, and photorefractive devices are discussed.

Realization of real-time interactive 3D image holographic display [Invited]

Realization of a 3D image holographic display supporting real-time interaction requires fast actions in data uploading, hologram calculation, and image projection. These three key elements will be reviewed and discussed, while algorithms of rapid hologram calculation will be presented with the corresponding results. Our vision of interactive holographic 3D displays will be discussed.