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Terahertz electron paramagnetic resonance generalized spectroscopic ellipsometry : The magnetic response of the nitrogen defect in 4H-SiC

We report on terahertz (THz) electron paramagnetic resonance generalized spectroscopic ellipsometry (THz-EPR-GSE). Measurements of field and frequency dependencies of magnetic response due to spin transitions associated with nitrogen defects in 4H-SiC are shown as an example. THz-EPR-GSE dispenses with the need of a cavity, permits independently scanning field and frequency parameters, and does no

Asymmetrical Flow Field-Flow Fractionation in the Separation, Characterization and Application of Wine Particle Matter

Wine particle matter is mainly constituted by wine colloids and wine macromolecules. These wine colloidal and macromolecular compounds are barely studied, possibly due to the difficulty in facing the challenges that their study merits. These compounds are mainly formed by polyphenols, proteins and polysaccharides that come from the grape seeds, skins and pulp and even, to a lesser extent, from the

Infrared dielectric functions and Brillouin zone center phonons of

We determine the anisotropic dielectric functions of rhombohedral α-Ga2O3 by far-infrared and infrared generalized spectroscopic ellipsometry and derive all transverse optical and longitudinal optical phonon mode frequencies and broadening parameters. We also determine the high-frequency and static dielectric constants. We perform density functional theory computations and determine the phonon dis

Analysis of temperature-dependent and time-resolved ellipsometry spectra of Ge

The dielectric function of Ge measured with static and time-resolved spectroscopic ellipsometry is analyzed using linear filtering techniques to investigate the temperature dependence of the direct band gap, as well as the temporal evolvement of critical points obtained from femtosecond pumpprobe ellipsometry measurements.

Transient birefringence and dichroism in ZnO studied with fs-time-resolved spectroscopic ellipsometry

The full transient dielectric-function (DF) tensor of ZnO after UV-laser excitation in the spectral range 1.4-3.6 eV is obtained by measuring an m-plane-oriented ZnO thin film with femtosecond (fs)-time-resolved spectroscopic ellipsometry. From the merits of the method, we can distinguish between changes in the real and the imaginary part of the DF as well as changes in birefringence and dichroism

Broadband femtosecond spectroscopic ellipsometry

We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellip

ELI beamlines user oriented high-harmonic beamline

We present latest progress and experimental capabilities of user-oriented XUV beamline based on high harmonic generation (HHG). The focal length of the HHG was recently extended to 5 meters, upscaling the overall XUV photon flux.

Ultrafast dynamics of hot charge carriers in an oxide semiconductor probed by femtosecond spectroscopic ellipsometry

Many linked processes occur concurrently in strongly excited semiconductors, such as interband and intraband absorption, scattering of electrons and holes by the heated lattice, Pauli blocking, bandgap renormalization and the formation of Mahan excitons. In this work, we disentangle their dynamics and contributions to the optical response of a ZnO thin film. Using broadband pump-probe ellipsometry

Spectral and polarization properties of VUV-mirrors for experiments at a HHG beamline

For polarization-resolved reflection experiments such as ellipsometry, not only is high reflectivity in a wide spectral range required for mirrors but also the quality of their polarization response is important. Furthermore, for VUV ellipsometry, optimal angles of incidence at the sample are between 45° and 60° with respect to the surface normal. In the best case, a setup should even allow variab

Pulsed laser deposited transparent and conductive V-doped ZnO thin films

ZnO and vanadium-doped ZnO (0.7–4.1 at.%) thin films were deposited onto corning glass substrates by the pulsed laser deposition technique using a KrF excimer laser (λ = 248 nm). The films were deposited at 500 °C under an oxygen pressure of 1 Pa with a laser fluence of 2 J/cm2. The structural, morphological, optical and electrical properties as a function of the dopant atomic concentration were i

Characterization of the high harmonics source for the VUV ellipsometer at ELI Beamlines

In this paper, the authors present the characterization experiments of a 20 fs vacuum ultraviolet beam from a high harmonic generation source. The beam hits a silicon sample and passes a triple reflection gold polarizer located inside an ultrahigh vacuum chamber. The polarizer's Malus curve was obtained; the total acquisition time for each point of the curve was 30 s. This aims to be the first vac

Voigt Exceptional Points in an Anisotropic ZnO-Based Planar Microcavity : Square-Root Topology, Polarization Vortices, and Circularity

Voigt points represent propagation directions in anisotropic crystals along which optical modes degenerate, leading to a single circularly polarized eigenmode. They are a particular class of exceptional points. Here, we report the fabrication and characterization of a dielectric, anisotropic optical microcavity based on nonpolar ZnO that implements a non-Hermitian system and mimics the behavior of

Pilot-Scale Protein Recovery from Cold-Pressed Rapeseed Press Cake : Influence of Solids Recirculation

The agricultural sector is responsible for about 30% of greenhouse gas emissions, and thus there is a need to develop new plant-based proteins with lower climate impact. Rapeseed press cake, a by-product from rapeseed oil production, contains 30% high-quality protein. The purpose of this study was to recover protein from cold-pressed rapeseed press cakes on a pilot scale using a decanter and inves

Progress on laser-driven X-ray sources at ELI Beamlines

Three main paths are being developed within the ELI research program for transforming driving laser pulses into bursts of bright short wavelength radiation: high-order harmonic generation in gases, plasma X-ray sources and sources based on relativistic electron beams accelerated in laser plasma. For each of these research areas, dedicated beamlines are built to provide a unique combination of X-ra

Transient dielectric functions of Ge, Si, and InP from femtosecond pump-probe ellipsometry

Transient dielectric functions with a 120 fs time resolution of Ge, Si, and InP were acquired from 1.7 to 3.5 eV with a femtosecond pump-probe rotating-compensator ellipsometer. The intensity of the pump laser (with 1.55, 3.10, or 4.65 eV photon energy) was adjusted to create an initial near-surface carrier density of 1020 cm-3. In Ge, there is a significant (∼15%) decrease in the E1 and E1 + Δ1 c

On the Optical Properties of Thin-Film Vanadium Dioxide from the Visible to the Far Infrared

The insulator-to-metal transition (IMT) in vanadium dioxide (VO2) can enable a variety of optics applications, including switching and modulation, optical limiting, and tuning of optical resonators. Despite the widespread interest in VO2 for optics, the wavelength-dependent optical properties across its IMT are scattered throughout the literature, are sometimes contradictory, and are not available

Exceptional Points in the Dispersion of Optically Anisotropic Planar Microcavities

When incorporating anisotropic materials, planar microcavities can give rise to exceptional points, i.e. propagation directions along which two otherwise polarization-split photonic modes degenerate in energy and broadening. They are non-Hermitian degeneracies revealing complex-square-root topology and chiral eigenstates. We show computations and experiments on ZnO-based microcavities.

Epsilon-Near-Zero Substrate Engineering for Ultrathin-Film Perfect Absorbers

Efficient suppression of reflection is a key requirement for perfect absorption of light. Recently, it has been shown that reflection can be effectively suppressed utilizing a single ultrathin film deposited on metals or polar materials featuring phonon resonances. The wavelength at which reflection can be fully suppressed is primarily determined by the nature of these substrates and is pinned to

Exceptional points in anisotropic photonic structures : From non-Hermitian physics to possible device applications

We demonstrate that exceptional points exist in fully transparent, optically "effectively" biaxial, anisotropic micro-cavities, fabricated using an uniaxial cavity material with its axis inclined to the Bragg mirror growth direction. This is similar to the existence of singular (optic) axes in absorbing biaxial crystals, but the lack of time reversal symmetry is mediated by the mode broadening, i.

Exceptional points in anisotropic planar microcavities

Planar microcavities allow the control and manipulation of spin polarization, manifested in phenomena like the optical spin Hall effect due to the intrinsic polarization mode splitting. Here, we study a transparent microcavity with broken rotational symmetry, realized by aligning the optic axis of a uniaxial cavity material in the cavity plane, giving rise to exceptional points in the dispersion r