Photochromic materials are a family of compounds which can undergo reversible photo-switches between two different states or isomers with remarkably different properties. Inspired by their smart photo-switchable characteristics, a variety of light-driven functional materials have been exploited, such as ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, optic/electronic devices, sensors, bio-imaging and so on. This review commences with a brief description of exciting progress in this field, from systems in solution to modified functional surfaces. Further development of these photo-switchable systems into practical applications as well as existing challenges are also discussed and put in prospect.

Photochromic Materials: More Than Meets The Eye

Azopolymers comprise a unique materials platform, in which the photoisomerization reaction of azobenzene mole- cules can induce substantial material motions at molecular, mesoscopic, and even macroscopic length scales. In particular, amorphous azopolymer films can form stable surface relief pat- terns upon exposure to interfering light. This allows obtaining large-area periodic micro- and nanostructures in a remarkably simple way. Herein, recent progress in the development of azopolymer-based surface-patterning techniques for photonic applications is reviewed. Starting with a thin azopolymer layer, one can create a variety of photonic elements, such as diffrac- tion gratings, microlens arrays, plasmonic sensors, antireflec- tion coatings, and nanostructured light-polarization converters, either by using the azopolymer surface patterns themselves as optical elements or by utilizing them to microstructure or nanostructure other materials. Both of these domains are cov- ered, with the aim of triggering further research in this fasci- nating field of science and technology that is far from being harnessed. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 00, 000-000

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/polb.23390

Azopolymer‐based micro‐ and nanopatterning for photonic applications

The development of solid materials that can be reversibly interconverted by light between forms with different physico-chemical properties is of great interest for separation, catalysis, optoelectronics, holography, mechanical actuation and solar energy conversion. Here, we describe a series of shape-persistent azobenzene tetramers that form porous molecular crystals in their E-configuration, the porosity of which can be tuned by changing the peripheral substituents on the molecule. Efficient E→Z photoisomerization of the azobenzene units takes place in the solid state and converts the crystals into a non-porous amorphous melt phase. Crystallinity and porosity are restored upon Z→E isomerization promoted by visible light irradiation or heating. We demonstrate that the photoisomerization enables reversible on/off switching of optical properties such as birefringence as well as the capture of CO2 from the gas phase. The linear design, structural versatility and synthetic accessibility make this new family of materials potentially interesting for technological applications.

/pdf/photoinduced-reversible-switching-of-porosity-in-molecular-3bgs1chkot.pdf

Photoinduced reversible switching of porosity in molecular crystals based on star-shaped azobenzene tetramers

A holographic display system for realizing a three-dimensional optical see-through augmented reality (AR) is proposed. A multi-functional holographic optical element (HOE), which simultaneously performs the optical functions of a mirror and a lens, is adopted in the system. In the proposed method, a mirror that is used to guide the light source into a reflection type spatial light modulator (SLM) and a lens that functions as Fourier transforming optics are recorded on a single holographic recording material by utilizing an angular multiplexing technique of volume hologram. The HOE is transparent and performs the optical functions just for Bragg matched condition. Therefore, the real-world scenes that are usually distorted by a Fourier lens or an SLM in the conventional holographic display can be observed without visual disturbance by using the proposed mirror-lens HOE (MLHOE). Furthermore, to achieve an optimized optical recording condition of the MLHOE, the optical characteristics of the holographic material are measured. The proposed holographic AR display system is verified experimentally.

Holographic display for see-through augmented reality using mirror-lens holographic optical element.

A novel system of optical see-through augmented reality (AR) is proposed by making use of a holographic optical element (HOE) with full-color and lens-array functions. The full-color lens-array HOE provides see-through property with three-dimensional (3D) virtual images, for it functions as a conventional lens array only for Bragg-matched lights. An HOE recording setup was built, and it recorded a 30 mm × 60 mm sized full-color lens-array HOE by using the techniques of spatial multiplexing for large-area recording and wavelength multiplexing for full-color imaging. The experimental results confirm that the suggested full-color lens-array HOE can provide the full-color 3D virtual images in the optical see-through AR system.

Full-color lens-array holographic optical element for three-dimensional optical see-through augmented reality

Optical data storage has had a major impact on daily life since its introduction to the market in 1982. Compact discs (CDs), digital versatile discs (DVDs), and Blu-ray discs (BDs) are universal data-storage formats with the advantage that the reading and writing of the digital data does not require contact and is therefore wear-free. These formats allow convenient and fast data access, high transfer rates, and electricity-free data storage with low overall archiving costs. The driving force for development in this area is the constant need for increased data-storage capacity and transfer rate. The use of holographic principles for optical data storage is an elegant way to increase the storage capacity and the transfer rate, because by this technique the data can be stored in the volume of the storage material and, moreover, it can be optically processed in parallel. This Review describes the fundamental requirements for holographic data-storage materials and compares the general concepts for the materials used. An overview of the performance of current read-write devices shows how far holographic data storage has already been developed.

From the surface to volume: concepts for the next generation of optical-holographic data-storage materials.

This paper describes a new class of recording materials for volume holographic applications suitable to meet commercial
manufacturing needs. These next-generation holographic photopolymers have the ability to satisfy the unmet demand
for color and depth tuning that is only possible with volume holograms. Unlike earlier holographic photopolymers, these
new materials offer the advantages of no chemical or thermal processing combined with low shrinkage and detuning.
Furthermore, these materials exhibit high transparency, a high resolution of more than 5000 lines/mm and are
environmentally robust. Bayer MaterialScience plans to commercialize these materials, which combine excellent
holographic characteristics with compatibility to mass-production processes. In this paper, we will briefly discuss the
potential markets and applications for a new photopolymer, describe the attributes of this new class of photopolymers,
relate their ease of use in holographic recording, and discuss potential applications of such materials..

http://www2.engr.arizona.edu/~ece527/Bayer%20SPIE.pdf

New recording materials for the holographic industry

We have been developing a new class of recording materials for volume holography, offering the advantages for full
color recording and depth tuning without any chemical or thermal processing, combined with low shrinkage and
detuning. These photopolymers are based on the two chemistry concept in which the writing chemistry is dissolved in a
preformed polymeric network. This network gives the necessary mechanical stability to the material prior to recording.
In this paper we show that the recording process in these materials can be successfully described within a reactiondiffusion
model. For the first time the combination of plane-wave recording data in transmission and reflection geometry
was used to extract the model parameters. This was achieved via a master curve construction of the respective power
density response functions of the photopolymer at saturation recording conditions. Within that model, power density
response, spatial frequency response, non-locality effects, beam ratio effects and even dosage response can be predicted
and explained for a wide range of CW recording conditions which are important for various holographic applications of
these new materials.

Reaction-diffusion model applied to high resolution Bayfol HX photopolymer

We have been developing a new class of recording materials for volume holography, offering the advantages of full
color recording and depth tuning without any chemical or thermal processing, combined with low shrinkage and
detuning. These photopolymers are based on the two-chemistry concept in which the writing chemistry is dissolved in a
preformed polymeric network. This network gives the necessary mechanical stability to the material prior to recording.
In this paper we describe several aspects of holographic recording into Bayfol® HX which are beneficial for its effective
use and discuss them within a more elaborate reaction-diffusion model. Inhibition phenomena and the influence of precure
are studied within this model and are investigated experimentally for single hologram recording and angular
multiplexed hologram recordings. Also the dark reaction after the exposure period and the minimum allowable waiting
time for full hologram formation are addressed. The proper understanding of these phenomena is important for the
optimal usage of these new materials, in for example step-and-repeat mass production of holograms.

Holographic recording aspects of high-resolution Bayfol HX photopolymer

The invention relates to a method for producing holographic films, in which a photopolymer formulation is provided which comprises as constituents matrix polymers, writing monomers, a photoinitiatior system, optionally a non-photopolymerizable component and optionally catalysts, radical stabilizers, solvents, additives and other auxiliaries and/or additives. The photopolymer formulation is applied in a planar manner and in the form of a film on a support film and the photopolymer formulation is dried on the support film at a temperature 60 100 DEG C and are above the temperature T by at least 30 DEG C, and a photopolymer formulation having a plateau module of =0.030 MPa is used.

Marc-Stephan Weiser

Papers

From the surface to volume: concepts for the next generation of optical-holographic data-storage materials.

New recording materials for the holographic industry

Reaction-diffusion model applied to high resolution Bayfol HX photopolymer

Holographic recording aspects of high-resolution Bayfol HX photopolymer

Method for producing a holographic film