Christian Pruner

Neutron optical beam splitter from holographically structured nanoparticle-polymer composites.

We report a breakthrough in the search for versatile diffractive elements for cold neutrons. Nanoparticles are spatially arranged by holographical means in a photopolymer. These grating structures show remarkably efficient diffraction of cold neutrons up to about 50% for effective thicknesses of only 200   μm. They open up a profound perspective for next generation neutron-optical devices with the capability to tune or modulate the neutron diffraction efficiency.

Photopolymerizable nanocomposite photonic materials and their holographic applications in light and neutron optics

We present an overview of recent investigations of photopolymerizable nanocomposite photonic materials in which, thanks to their high degree of material selectivity, recorded volume gratings possess high refractive index modulation amplitude and high mechanical/thermal stability at the same time, providing versatile applications in light and neutron optics. We discuss the mechanism of grating formation in holographically exposed nanocomposite materials, based on a model of the photopolymerization-driven mutual diffusion of monomer and nanoparticles. Experimental inspection of the recorded grating’s morphology by various physicochemical and optical methods is described. We then outline the holographic recording properties of volume gratings recorded in photopolymerizable nanocomposite materials consisting of inorganic/organic nanoparticles and monomers having various photopolymerization mechanisms. Finally, we show two examples of our holographic applications, holographic digital data storage and slow-neutron beam control.

Mirrors for slow neutrons from holographic nanoparticle-polymer free-standing film-gratings

We report on successful tests of holographically arranged grating-structures in nanoparticle-polymer composites in the form of 100 microns thin free-standing films, i.e. without sample containers or covers that could cause unwanted absorption/incoherent scattering of very-cold neutrons. Despite their large diameter of 2 cm, the flexible materials are of high optical quality and yield mirror-like reflectivity of about 90% for neutrons of 4.1 nm wavelength.

Nanoparticle polymer composite volume gratings incorporating chain transfer agents for holography and slow-neutron optics

We demonstrate twofold enhancement of the saturated refractive index modulation (Δn(sat)) recorded in a photopolymerizable nanoparticle-acrylate polymer composite film by incorporating thiols acting as chain transfer agents. The chain transfer reaction of thiols with (meth)acrylate monomer reduces the polymer crosslinking density and facilitates the mutual diffusion of nanoparticles and monomer during holographic exposure. These modifications provide increased density modulations of nanoparticles and the formed polymer, resulting in the enhancement of Δn(sat) as high as 1.6×10(-2) at a wavelength of 532 nm. The incorporation of thiols also leads to shrinkage suppression and to improvement of the gratings spatial frequency response. Such simultaneous improvement is very useful for holographic applications in light and neutron optics.

Mid-infrared absorptance of silicon hyperdoped with chalcogen via fs-laser irradiation

Silicon hyperdoped with heavy chalcogen atoms via femtosecond-laser irradiation exhibits strong broadband, sub-bandgap light absorption. Understanding the origin of this absorption could enable applications for hyperdoped-silicon based optoelectronic devices. In this work, we measure absorption to wavelengths up to 14 μm using Fourier transform infrared spectroscopy and study sulfur-, selenium-, and tellurium-hyperdoped Si before and after annealing. We find that absorption in the samples extends to wavelengths as far as 6 μm. After annealing, the absorption spectrum exhibits features that are consistent with free-carrier absorption. Although the surface morphology influences the shape of the absorption curves, the data permit us to place an upper bound on the position of the chalcogen dopant energy levels.

Three-port beam splitter for slow neutrons using holographic nanoparticle-polymer composite diffraction gratings

Diffraction of slow neutrons by nanoparticle-polymer composite gratings has been observed. By carefully choosing grating parameters such as grating thickness and spacing, a three-port beam splitter operation for slow neutrons—splitting the incident neutron intensity equally into the ±1st and the 0th diffraction orders—has been realized. As a possible application, a Zernike three-path interferometer is briefly discussed.

Diffraction gratings for neutrons from polymers and holographic polymer-dispersed liquid crystals

We discuss the applicability of holographically recorded gratings in photopolymers and holographic polymer-dispersed liquid crystals as neutron optical elements. An experimental investigation of their properties for light and neutrons with different grating spacings and grating thicknesses is performed. The angular dependences of the diffraction efficiencies for those gratings are interpreted in terms of a rigorous coupled wave analysis. Starting from the obtained results we work out the lines for the production of an optimized neutron optical diffraction grating, i.e. high diffraction efficiency in the Bragg diffraction regime with moderate angular selectivity.

Effects of chain-transferring thiol functionalities on the performance of nanoparticle-polymer composite volume gratings

We report influences of varying functionalities of thiols as chain transfer agents on the spatial frequency response, polymerization shrinkage, and thermal stability of a volume grating recorded in a photopolymerizable ZrO₂ nanoparticle-polymer composite film. It is shown that a substantial increase in the saturated refractive index modulation is realized at high spatial frequencies by doping with multifunctional thiols. Moreover, the incorporation of multifunctional thiols considerably suppresses polymerization shrinkage of recorded volume gratings and thermal changes in refractive index and film thickness as compared with the case of mono-thiol. These results indicate that multifunctional thiols provide effective control of the properties of nanoparticle-polymer composite volume gratings for various applications in light and neutron optics.

Holographic Gratings for Slow-Neutron Optics

Recent progress in the development of holographic gratings for neutron-optics applications is reviewed. We summarize the properties of gratings recorded in deuterated (poly)methylmethacrylate, holographic polymer-dispersed liquid crystals and nanoparticle-polymer composites revealed by diffraction experiments with slow neutrons. Existing and anticipated neutron-optical instrumentations based on holographic gratings are discussed.

Neutron-optical gratings from nanoparticle-polymer composites

Abstract The preparation of neutron-optical phase gratings with light-optical holography is reviewed. We compare the relevant concepts of: (i) Kogelniks theory for Bragg diffraction of light by thick volume gratings, which can be used to analyze holographic gratings with both light and neutrons, and (ii) the dynamical theory of neutron diffraction. Without going into mathematical detail, we intend to illuminate their correspondence. The findings are illustrated by analyzing data obtained from reconstruction of nanoparticle holographic gratings with both light and neutrons.