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Recent progress in nanofabrication has redrawn the boundaries of the applicability of chiroptical (chiral optical) effects. Chirality, often expressed as a twist in biomolecules, is crucial for pharmaceuticals, where it can result in extremely different chemical properties. Because chiroptical effects are typically very weak in molecules, plasmonic nanomaterials are often proposed as a promising platform to significantly enhance these effects. Unfortunately, the ideal plasmonic nanomaterial has conflicting requirements: its chirality should enhance that of the chiral molecules and yet it should have no chiroptical response on its own. Here, we propose a unique reconciliation to satisfy the requirements: a racemic plasmonic nanomaterial, consisting of equal amounts of opposite chiral unit cells. We show how diffraction spectroscopy can be used to unveil the presence of chirality in such racemic nanogratings in the far-field. Our experiments are supported by numerical simulations and yield a circular intensity difference of up to 15%. The physical origin is demonstrated by full wave simulations in combination with a Green's function – group-theory-based analysis. Contributions from Circular Dichroism in the Angular Distribution of Photoelectrons (CDAD) and pseudo/extrinsic chirality are ruled out. Our findings enable the far-field measurement and tuning of racemic nanomaterials, which is crucial for hyper-sensitive chiral molecular characterization.

Based on the authors’ computations of cross-sections of the basic processes which form continuous absorption in the photospheres of solar-type stars, the spectral dependence of the solar radiation intensity in the continuous spectrum in the visible and infrared regions has been investigated. It is shown that the depression observed in the continuous spectrum of solar radiation in the region (6500 − 8200) ˚A is caused by the processes of photoionization of neutral hydrogen atoms excited up to the energy levels with the principal quantum number n = 3. The results of computation are in good agreement with the data observed.

In this work is examined a new modeling way of describing the continuous absorption of electromagnetic (EM) radiation in a dense partially ionized hydrogen plasmas with electron densities about $5\cdot10^{18}$ cm$^{-3}$ - $1.5\cdot10^{19}$cm$^{-3}$ and temperatures about $1.6 \cdot10^{4}$ K - $2.5 \cdot 10^{4}$ K in the wavelength region $300 \textrm{nm} < \lambda < 500 \textrm{nm}$. The obtained results can be applied to the plasmas of the partially ionized layers of different stellar atmospheres.

International audience; Measurements of circular dichroism in the angular dependence (CDAD) of photoemission from core levels and valence bands of the ZnSe(001)-c(2x2) surface are presented. Due to the lowering of the surface symmetry compared to the bulk, the CDAD of surface-related spectral components and of bulk components exhibit different polar variations. We propose a way to identify experimentally surface-related bands in the valence-band photoemission spectra based on these symmetry considerations.