Roadmap on holography

From its inception holography has proven an extremely productive and attractive area of research. While specific technical applications give rise to 'hot topics', and three-dimensional (3D) visualisation comes in and out of fashion, the core principals involved continue to lead to exciting innovations in a wide range of areas. We humbly submit that it is impossible, in any journal document of this type, to fully reflect current and potential activity; however, our valiant contributors have produced a series of documents that go no small way to neatly capture progress across a wide range of core activities. As editors we have attempted to spread our net wide in order to illustrate the breadth of international activity. In relation to this we believe we have been at least partially successful.This work was supported by Ministerio de Economía, Industria y Competitividad (Spain) under projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and FIS2015-66570-P (MINECO/FEDER), and by Generalitat Valenciana (Spain) under project PROMETEO II/2015/015

Photo-induced structural transformation in sol-gel derived silica-methacrylate composites

We describe our investigations into photochemical and micro-structural characteristics of sol-gel derived silica-methacrylate composites (SAC). Upon irradiation with UV light, thin SAC films undergo spatially localised increases of the index of refraction, a macroscopic property that has been used in the photo-lithography of passive integrated optics devices. Our spectroscopic studies indicate that UV initiated free-radical polymerisation of methacrylate substituents trigger further growth and densification of the silica host. This advances our molecular level understanding of photo-reactions in hybrid organo-silica networks.We examine laser-initiated organic chain growth in SAC planar waveguides. Optical modes initiate polymerisation of methacrylate substituents along the propagation path. In turn, the nascent reaction medium presents a non-uniform refractive index profile to the guided laser beam. Spatially localised and intensity-dependent refractive index changes create a lens-like profile in the medium. As a result, the beam self-focuses along its propagation axis without diffraction.We describe oriented organic chain growth in the nonlinear optical and highly anisotropic reaction field provided by a linearly polarised, self-focusing laser beam. A self-focusing laser beam induces an anisotropy in the refractive index profile of SAC waveguides. We characterise laser-induced birefringence in the hybrid network through polarised waveguide Raman spectroscopy and optical birefringence measurements.Long-range periodic self-organisation in sol-gel derived silica acrylate composites formed in the absence of external templates was observed for the first time. Significantly, the periodicity associated with this structure is approximately 200 nm, approaching the optical wavelength regime

Cicada sanguinolenta

We report that incandescent beams patterned with amplitude depressions (dips) suffer instability in a photopolymerizable system and organize into lattices of black and bright self-trapped beams propagating respectively, through self-induced black and bright waveguides. Such optochemically organized lattices emerge when beams embedded with a hexagonal or square array of dips initiate free-radical polymerization and corresponding changes in refractive index (Δ<i>n</i>) along their propagation paths. Under these nonlinear conditions, the dips evolve into a hexagonal or square lattice of black beams, while their bright interstitial regions become unstable and divide spontaneously into multiple filaments of light. These filaments have a characteristic diameter (<i>d</i>_f) and organize into a variety of geometries, which are determined by the shape and dimensions of the bright interstices. At interstitial widths > 2<i>d</i>_f, filaments are randomly positioned in space, whereas at widths < 2<i>d</i>_f, the interstices are occupied by a single file of filaments encircling each dark channel. When the interstitial width ≈ <i>d</i>_f, the filaments organize into lattices with long-range hexagonal or square symmetry. By employing anisotropic interstices such as rectangles, filamentation can be selectively elicited along the long axis, leading to a lattice of filament doublets. This work demonstrates the versatility and significant potential of optochemical organization to generate complex, optically functional polymer lattices, which cannot be constructed through conventional lithography or self-assembly. Specifically, the study introduces a new generation of waveguide lattices, in which light propagation is co-operatively managed by black and bright waveguides; the former suppress local light propagation and, in this way, enhance light confinement and guidance in proximal bright waveguides

Spontaneous Formation of Fractal Aggregates of Au Nanoparticles in Epoxy-Siloxane Films and Their Application as Substrates for NIR Surface Enhanced Raman Spectroscopy

We present a facile, inexpensive route to free-standing, thermo-mechanically robust and flexible epoxy-siloxane substrates embedded with fractal aggregates of Au nanoparticles, and demonstrate their efficiency as substrates for surface enhanced Raman spectroscopy (SERS) at NIR wavelengths. The metallodielectric films are prepared by generating Au nanoparticles through the in-situ reduction of gold (III) chloride trihydrate in epoxypropoxypropyl terminated polydimethyl siloxane (EDMS). The metal nanoparticles spontaneously aggregate into fractal structures in the colloid, which could then be drop-cast onto a substrate. Subsequent UV-initiated cationic polymerization of epoxide moieties in EDMS transforms the fluid colloid into a thin, free-standing film, which contains a dense distribution of fractal aggregates of Au nanoparticles. We used electron and optical microscopy as well as UV–Vis–NIR spectrometry to monitor the evolution of nanoparticles and to optically and structurally characterize the resulting films. Raman spectroscopy of the chromophore Eosin Y adsorbed onto the metallodielectric films showed that they are excellent SERS substrates at NIR excitation with an enhancement factor of ~9.3 × 103

Optochemical Organization in a Spatially Modulated Incandescent Field: A Single-Step Route to Black and Bright Polymer Lattices

We report that incandescent beams patterned with amplitude depressions (dips) suffer instability in a photopolymerizable system and organize into lattices of black and bright self-trapped beams propagating respectively, through self-induced black and bright waveguides. Such optochemically organized lattices emerge when beams embedded with a hexagonal or square array of dips initiate free-radical polymerization and corresponding changes in refractive index (Δ<i>n</i>) along their propagation paths. Under these nonlinear conditions, the dips evolve into a hexagonal or square lattice of black beams, while their bright interstitial regions become unstable and divide spontaneously into multiple filaments of light. These filaments have a characteristic diameter (<i>d</i>_f) and organize into a variety of geometries, which are determined by the shape and dimensions of the bright interstices. At interstitial widths > 2<i>d</i>_f, filaments are randomly positioned in space, whereas at widths < 2<i>d</i>_f, the interstices are occupied by a single file of filaments encircling each dark channel. When the interstitial width ≈ <i>d</i>_f, the filaments organize into lattices with long-range hexagonal or square symmetry. By employing anisotropic interstices such as rectangles, filamentation can be selectively elicited along the long axis, leading to a lattice of filament doublets. This work demonstrates the versatility and significant potential of optochemical organization to generate complex, optically functional polymer lattices, which cannot be constructed through conventional lithography or self-assembly. Specifically, the study introduces a new generation of waveguide lattices, in which light propagation is co-operatively managed by black and bright waveguides; the former suppress local light propagation and, in this way, enhance light confinement and guidance in proximal bright waveguides

A Black Beam Borne by an Incandescent Field Self-Traps in a Photopolymerizing Medium

We report that a self-trapped black optical beam that is spatially and temporally incoherent forms spontaneously in a nascent photopolymerization system. The black beam inscribes a permanent cylindrical channel, which prevents the propagation of visible light even under passive conditions (in the absence of polymerization). The finding opens a powerful new mechanism to manipulate light signals from incoherent sources such as LEDs through selective suppression of light propagation. This contrasts with approaches employed by photonic crystals and optical waveguides, which concentrate and guide light intensity within spatially localized regions. The self-trapped black beam forms when a broad incandescent beam bearing a negligible depression was launched into a photopolymerizable medium. Because of refractive index changes caused by polymerization, the depression narrows, deepens, and continually rejects the visible spectrum of light until it stabilizes as a black beam that propagates over long distances (≫ effective Rayleigh range) without significant divergence. As refractive index changes due to polymerization are irreversible, the cylindrical region occupied by the self-trapped black beam is inscribed as a black channel waveguide in the medium

Optochemical Organization in a Spatially Modulated Incandescent Field: A Single-Step Route to Black and Bright Polymer Lattices

We report that incandescent beams patterned with amplitude depressions (dips) suffer instability in a photopolymerizable system and organize into lattices of black and bright self-trapped beams propagating respectively, through self-induced black and bright waveguides. Such optochemically organized lattices emerge when beams embedded with a hexagonal or square array of dips initiate free-radical polymerization and corresponding changes in refractive index (Δ<i>n</i>) along their propagation paths. Under these nonlinear conditions, the dips evolve into a hexagonal or square lattice of black beams, while their bright interstitial regions become unstable and divide spontaneously into multiple filaments of light. These filaments have a characteristic diameter (<i>d</i>_f) and organize into a variety of geometries, which are determined by the shape and dimensions of the bright interstices. At interstitial widths > 2<i>d</i>_f, filaments are randomly positioned in space, whereas at widths < 2<i>d</i>_f, the interstices are occupied by a single file of filaments encircling each dark channel. When the interstitial width ≈ <i>d</i>_f, the filaments organize into lattices with long-range hexagonal or square symmetry. By employing anisotropic interstices such as rectangles, filamentation can be selectively elicited along the long axis, leading to a lattice of filament doublets. This work demonstrates the versatility and significant potential of optochemical organization to generate complex, optically functional polymer lattices, which cannot be constructed through conventional lithography or self-assembly. Specifically, the study introduces a new generation of waveguide lattices, in which light propagation is co-operatively managed by black and bright waveguides; the former suppress local light propagation and, in this way, enhance light confinement and guidance in proximal bright waveguides