arXiv subjects

Jürgen Klepp

Publications and source records attributed to Jürgen Klepp.

4 recordsLinked to original sources

arXiv2026

Commissioning measurements for a very cold neutron interferometer based on nanodiamond-polymer composite gratings

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.

physics.optics↗

arXiv2025

Holographic hyperbranched polymer nanocomposite grating with exceptionally large neutron scattering length density modulation amplitudes

Nanoparticle-polymer composite gratings incorporating ultrahigh-refractive-index hyperbranched polymers as organic nanoparticles have demonstrated exceptional light optical properties, yet their potential for neutron diffraction applications remains unexplored. We report on the neutron optical properties of a holographically structured hyperbranched-polymer-dispersed nanocomposite grating at a quasi-monochromatic neutron wavelength of 2 nm. We show that neutron diffraction measurements performed at the SANS-I instrument of the Paul Scherrer Institute (Switzerland) reveal exceptionally high neutron scattering length density modulation amplitudes. These scattering length density modulation amplitudes are the highest reported to date. Very high neutron diffraction efficiency is expected with the use of thicker uniform gratings and longer neutron wavelengths, with low angular and wavelength selectivity constraints.

physics.optics↗

arXiv2019

Evolution of nematic and ferromagnetic ordering in suspensions of magnetic nanoplatelets

Suspensions of magnetic nanoplatelets in isotropic solvents are very interesting examples of ferrofluids. It has been shown that above a certain concentration ΦNI such suspensions form a ferromagnetic nematic phase, which makes this system a unique example of a dipolar fluid. The formation of a nematic phase is driven by anisotropic electrostatic and long-range dipolar magnetic interactions. Here, we present studies of the evolution of short range positional and orientational magnetic order in the suspensions with volume fractions below and above ΦNI, using small angle neutron scattering (SANS). The results show that in the absence of an external magnetic field, short range positional and orientational order already exist at relatively low volume fractions. Polarized SANS revealed that the contribution of ferromagnetic ordering to the formation of the nematic phase is significant. The ferromagnetic correlations can be qualitatively explained by a simple model, which takes into account anisotropic screened electrostatic and dipolar magnetic interactions.

cond-mat.soft↗

arXiv2013

Far off-Bragg reconstruction of volume holographic gratings: A comparison of experiment and theories

We performed light optical diffraction experiments on a nanoparticle-polymer volume holographic grating in an angular range including also far off-Bragg replay. A comparison of three diffraction theories - on the same level of complexity - with our experimental results shows that the dynamical theory of diffraction and the first-order two-wave coupling theory using the beta-value method fit the data very well. In contrast, the prevalent two-wave coupling theory using the K-vector closure method yields a poor fit with an order of magnitude worse mean squared error. These findings must be considered for accurate determination of coupling strength and grating thickness.

physics.optics↗