Long-wavelength neutron interferometry using discrete optical elements is notoriously challenging due to stringent alignment and stability requirements. Here, we introduce a monolithic double-Laue neutron interferometer fabricated from a stack of commercial Bayfol HX photopolymer films. By recording holographic gratings simultaneously in multiple layers, we create a robust device that is inherently aligned, bypassing traditional stability problems. We demonstrate the device's function by observing the characteristic interference fringes in the diffracted intensity of both light and very cold neutrons. The interferometer is then used to perform in-situ characterization of the neutron beam's spectral profile, demonstrating its utility as a compact spectrometer. Our work establishes stacked holographic gratings as a simple, versatile, and powerful platform for matter-wave interferometry and metrology.

Over the past decade, holographic nanodiamond-polymer composite gratings have been developed and optimized as high-efficiency diffractive elements for very cold neutrons (VCN), for use as mirrors and beam splitters in a triple-Laue (LLL) interferometer. We report their optical characterization and, crucially, their neutron-optical performance, including diffraction efficiency and angular selectivity under VCN conditions. We further demonstrate their integration into a VCN interferometer. The layout of the interferometer and its first implementation at the beamline are described, highlighting practical considerations for long-term operation. We discuss avenues for performance improvement, in particular grating fabrication refinements. These results establish nanodiamond-polymer composite gratings as viable components for VCN interferometry and pave a way toward precision neutron phase measurements in the very cold regime.

In recent decades, photosensitive materials have been used for the development of optical devices not only for light, but also for cold and very cold neutrons. We show that holographically recorded gratings in nanodiamond-polymer composites (nDPC) form ideal diffraction elements for very cold neutrons. Their advantage of high diffraction efficiency, combined with low angular selectivity as a two-port beam splitter, meets the necessary conditions for application in a very cold neutron interferometer. We provide an overview of the latest achievements in the construction of such a triple Laue interferometer. A first operational test of the interferometer is planned immediately after this conference in May 2025.

Photosensitive materials with ever-improving properties are of great importance for optical and photonics applications. Additionally, they are extremely useful for designing components for neutron optical devices. We provide an overview on materials that have been tested and successfully used to control beams of cold and very cold neutrons based on diffractive elements. Artificial gratings are generated and optimized for the specific application in mind. We discuss the needs of the neutron optics community and highlight the progress obtained during the last decade. Materials that have been employed so far along with their properties are summarized, outlining the most promising candidates for the construction of an interferometer for very cold neutrons.

During the last decade a number of volume holographic media have been investigated that could serve not only as diffractive optical elements (DOEs) for light but also for slow neutrons. In this contribution we discuss the light optical properties of a stack of two gratings separated by an optically inert slice recorded in a Bayfol HX photopolymer. While the refractive-index modulation of the gratings for light is remarkable, the corresponding neutron optical analogue is, so far, in the medium range of other materials investigated. We therefore aim at possible improvements which are discussed in this manuscript.

Poly(methyl methacrylate) (PMMA) is a very versatile polymer which is used as a glass substitute or as an economical alternative to polycarbonate for many types of important applications, due to its particular physical properties. In this study we deal with the Raman spectroscopic characterization of the glass transition of PMMA, the value of the glass transition temperature being generally a decisive parameter for determining the application of polymers. The information obtained by two-dimensional correlation spectroscopy (2DCOS) analysis and perturbation-correlation moving-windows spectroscopy (PCMW2D) analysis of the temperature dependent depolarized Raman spectra enabled us to recognize that the glass transition of PMMA is ruled by intermolecular interactions which influence the vibrational modes of the molecular groups associated with ν(C[double bond, length as m-dash]O), δa(C-H) of α-CH3 and/or O-CH3, ν(C-O-C), ν(C-COO), and ν(C-C-O). This information was employed for the temperature dependent study of the Raman shift and of the full width at half maximum of the Raman peaks obtained through anisotropic and isotropic Raman spectra, of the depolarization ratio, of the Raman spectroscopic noncoincidence effect, and of the Raman peak intensities represented by Arrhenius-type plots, all results supporting the outcomes of this work. The comparison with results obtained by differential scanning calorimetry and with published results in molecular dynamics studies was also part of this work. As the main result, one can highlight the peak associated with the ν(C-O-C) stretching mode at around 812 cm-1 as the one which presents the better outcome for explaining the glass transition from the molecular point of view.

In the second part of our presentations we discuss the results of diffraction experiments from nanodiamond-polymer composite gratings performed with slow neutrons, i.e., at wavelengths longer than a nanometer. One goal of our investigations is to develop flexible, handy, low cost neutron diffractive optical elements (gratings) which can be tailored to serve as mirrors, two-port beamsplitters, multiport beamsplitters, polarizing beamsplitters or even can be assembled to form an interferometer. Basically three adjustable multiplicative parameters are decisive for the performance, i.e., the reflectivity or diffraction efficiency, of such gratings: the wavelength of the neutrons, the thickness and the neutron scattering density modulation of the grating. While the _rst is solely determined by the application one has in mind, the second parameter can be adjusted during the production process of the sample or by tilting the grating about an axis parallel to the grating vector, thus increasing the effective thickness. The third parameter, however, can only be tuned via the production process of the gratings but offers an enormous flexibility due to a variety of nanoparticles and the polymeric host materials at hand. For neutrons the important criteria are to design gratings having high coherent scattering length density modulation while avoiding incoherent scattering and absorption at the same time. For interferometric purposes an ideal grating will have high reflectivity and low angular selectivity. Here, we show first results obtained with nanodiamond-polymer composite gratings and outline potential ways to improvements.

We demonstrate the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive-index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. Nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. We describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the construction of transmission gratings in nanodiamond-polymer composite films, and light optical diffraction experiments. Results of slow-neutron diffraction from such gratings are also presented.

We investigate the applicability of polymer-ionic liquid composites as optical elements for light, as well as for slow neutrons. The gratings are recorded using two-beam mixing and are characterized experimentally based on their diffraction properties. We produced a set of samples differing in their thickness, ranging from 10 m - 100 m . We demonstrate that it is possible to prepare transmission gratings with a lattice constant of Λ = 480 n m , resulting in thick gratings for light, as well as neutrons. The presented samples show low optical losses in the Vis-UV spectrum and exhibit refractive index modulations of about 10 - 3 at λ = 543 n m . However, further improvements have to be made to obtain efficient neutron optical components.

Nanocomposites enable us to tune parameters that are crucial for use of such materials for neutron-optics applications. By careful choice of properties such as species (isotope) and concentration of contained nanoparticles, diffractive optical elements for long-wavelength neutrons are feasible. Nanocomposites for neutron optics have so far been tested successfully in protonated form, containing high amounts of 1H atoms, which exhibits rather strong neutron absorption and incoherent scattering. At a future stage of development, chemicals containing 1H could be replaced by components containing more favorable isotopes, such as 2H or 19F. In this note, we present results of Monte-Carlo simulations of the transmissivity of various nanocomposite materials for thermal and very-cold neutron spectra. Our simulation results for deuterated and fluorinated nanocomposite materials predict the losses due to absorption and scattering to be as low as 2%, as well as the broadening of the beam cross section to be negligible.

Photopolymerizable nanoparticle-polymer composite (NPC) is a photonic nanocomposite material consisting of photopolymer uniformly dispersed with nanoparticles (e.g., SiO 2 and ZrO 2 ). The distribution of dispersed nanoparticles can be manipulated holographically by light. This technique, the so-called holographic assembly of nanoparticles in polymer, enables us to perform the single step formation of large area photonic lattice structures for photonic applications such as holographic data storage, holographic diffractive elements and nonlinear optics. Furthermore, we showed that holographic NPC gratings could control slow-neutron (cold and very cold neutron) beams for neutron interferometer. Here we demonstrate for the first time the use of nanodiamonds (NDs), an intriguing allotrope of carbon, in NPCs to construct holographic NPC gratings with very large refractive index modulation amplitudes (Δn) and thus to efficiently control light and slow-neutron beams. This is possible because NDs have very high bulk refractive index at optical wavelengths and very large coherent and very small incoherent scattering cross sections with low absorption at slow-neutron wavelengths.

We report on the fabrication of novel nanocomposite gratings for holographic control of slow neutron beams. Plane-wave transmission gratings are recorded in photopolymerizable nanocomposite materials where nanoparticles are holographically assembled by visible light in a photopolymerizable monomer host. This all-optical assembling method provides the single step formation of large scale and multi-dimensional photonic lattice structures. Because nanoparticles and monomer can be selected for suitable applications, this nanocomposite material can be used not only for light beams but also for neutron beams. Here we show the use of surface-treated nanodiamonds and superparamagnetic Fe3O4 nanoparticles to record holographic transmission gratings for controlling a slow-neutron beam and selecting its spin states.

s – Invited talks Location: Ernst-Mach Lecture Hall 2 floor Cholesteric liquid crystal shells: from unique photonic crystal properties to applications in nonbiometric secure authentication tags Jan Lagerwall Physics & Materials Science Research Unit, University of Luxembourg, 1511 Luxembourg, Luxembourg, E­mail: jan.lagerwall@lcsoftmatter.com The colorful circularly polarized iridescence of short­pitch cholesteric liquid crystals (CLCs), arising due to Bragg reflection by the periodic internal helix structure, has fascinated scientists and laymen alike for more than a century. Recently, the peculiar effects arising when cholesterics are confined in samples with curved interfaces, such as droplets, shells and fibers, have received increasing attention [1]. Cholesteric shells are particularly interesting thanks to the rich optics arising when the axis of periodicity rotates continuously around the shell, with the added option of varying the shell thickness between top and bottom. The shell reflects light straight back to the observer regardless of viewing direction, and if a cluster of cholesteric shells in a plane is illuminated by white light, an intricate photonic cross communication pattern arises (left photo), with colourful spots arranged in a symmetry that reflects the arrangement of the shells [2­3]. If the shell is asymmetric with a thin top, light enters into the shell interior. The CLC inside then acts as a selective optical echo chamber that creates a colourful pattern of concentric rings (right photo) [4]. By changing the focus one can accentuate the internal reflection ring pattern or the external cross communication pattern, which is still present. The shells can be made durable and mechanically robust by polymerizing or polymer­stabilizing them, making large­scale application of the shells viable. For instance, by incorporating a cluster of CLC shells within an index matched solid matrix, a tag can be produced that generates the CLC shell patterns upon illumination, changing dynamically in response to which sample area is illuminated, to the focus, to the angle of illumination, and to the polarization and spectral content of the illuminating light. Moreover, since the spheres are arranged in a random fashion each tag is unique in a way that is out of control of the producer: not even the manufacturer of the original would be able to make a copy. In an interdisciplinary research thrust at the University of Luxembourg, involving computer and materials scientists, we are exploring the potential of using such CLC shell­based tags for secure authentication [5]. The tags could identify persons or be integrated in objects prone to counterfeiting, to prove the authenticity of the original product. Left: Patterns arising from communication between cholesteric shells, mediated by reflections on the sphere outsides. Right: A change in focus reveals that light enters through the thin top of these asymmetric shells, giving rise to different pattern of concentric colourful rings. [1] Urbanski, M. et al. Liquid crystals in micron­scale droplets, shells and fibers. J. Phys.: Condens. Matter

Yasuo Tomita , Akihisa Kageyama , Toshi Aoi , Yuko Iso , Koichi Umemoto , Jürgen Klepp , Christian Pruner 4 and Martin Fally 3 1 Department of Engineering. Science, University of Electro-Communication, Chofu, Tokyo 182-8585, Japan 2 Central Research Center, Daicel Corp., Himeji, Hyogo 671-1283, Japan 3 Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria 4 Department of Materials Science and Physics, University of Salzburg, A-5020 Salzburg, Austria Tel.: +81-424435164, fax: +81-424435208 E-mail: ytomita@uec.ac.jp

We fabricated a superparamagnetic ordered structure via self-assembly of a colloidal crystal from a suspension of maghemite nanoparticles and polystyrene beads. Such crystals are potential candidates for novel polarizing beam-splitters for cold neutrons, complementing the available methods of neutron polarization. Different bead sizes and nanoparticle concentrations were tested to obtain a crystal of reasonable quality. Neutron diffraction experiments in the presence of an external magnetic field were performed on the most promising sample. We demonstrate that the diffraction efficiency of such crystals can be controlled by the magnetic field. Our measurements also indicate that the Bragg diffraction regime can be reached with colloidal crystals.