Crossing the light line

We ask the question “what happens to Bloch waves in gratings synthetically moving at near the speed of light?”. First we define a constant refractive index (CRI) model in which Bloch waves remain well defined as they break the light barrier, then show their dispersion rotating through 360° from negative to positive and back again. Next we introduce the effective medium approximation (EMA) then refine it into a 4-wave model which proves to be highly accurate. Finally using the Bloch waves to expand a pulse of light we demonstrate sudden inflation of pulse amplitude combined with reversal of propagation direction as a luminal grating is turned on.

Terahertz Radiation Generation Process In The Medium Based On The Array of The Elongated Nanoparticles

We conduct a theoretical study and numerical simulations of terahertz radiation generation in the medium based on armchair-edge nanoribbons and zigzag nanotubes with metallic conductivity. The multicascade mechanism of radiation generation is considered in the task of terahertz radiation generation. The level of the injection current in nanoparticle arrays has been estimated. The task expands to the similar medium where radiation current is generated with the use of infrared radiation stimulated absorption, for example, radiation of a CO2 laser. Numerical results for the effective dielectric function have been obtained with the use of the effective medium-approximation, the Maxwell-Garnett’s theory and the Maxwell-Garnett model with the Clausius-Mossotti correction (geometrical model arrays).

Optical properties of Gobi dust and its pure compounds: experimental extinction spectra and complex refractive indices determination.

<p>Spectrometers are powerful instruments to detect atmospheric aerosols, especially on satellites since they allow measurements at a global scale and over different spectral ranges with high spectral resolution. However, to fully exploit their capabilities and to link optical properties, chemical composition and mass concentration, it is essential to have reference optical properties of various particles and mainly the complex refractive indices (CRI). The CRI of a natural aerosol source can be determined from a real sample of it or applying the effective medium approximation using the CRI of the pure compounds present in the natural sample. But in that case, it is necessary to know the mass fraction of each individual compound and above all their CRI. Nevertheless, the literature and CRI databases provide only reflectance measurements on bulk materials or pressed pellets and over a limited wavelength range (Querry <em>et al.</em>, 1987).</p><p>In the present work, dust from the Gobi desert is studied as it is the second most active dust source, after the Sahara desert, in terms of mass emissions (Querol <em>et al.</em>, 2019). For that extinction spectra have been recorded for natural Gobi dust sample and for its major compounds (Illite, Calcite and Quartz). Particles as a powder in a vessel are generated thanks to a magnetic stirring and a flow of nitrogen (Hubert <em>et al.</em>, 2017). The continuous flow of aerosols is directed into a 10-meters multipass cell fitted to a Fourier transform infrared spectrometer and a 1-meter singlepass cell within a UV-Visible spectrometer which cover a continuous spectral range from 650 cm<sup>-1</sup> to 40000 cm<sup>-1</sup>. Moreover, at the exit of the spectrometers the size distribution is recorded by an aerodynamic particle sizer and a scanning mobility particle sizer which allow to measure size particles from 14 nm to 20 µm. An inversion algorithm is carried out using experimental extinction spectra and the size distribution as input data (Herbin <em>et al.</em>, 2017). Applying the Mie theory and the single subtractive Kramers-Kröning integral, the real and the imaginary part of the CRI are retrieved at each wavelength with an optimal estimation method.</p><p>For the first time, CRI of Illite has been retrieved with a high spectral resolution (1 cm<sup>-1</sup>) and over a wide spectral range for suspended particles. For calcite and quartz particles, the crystalline phase has to be considered by introducing the ordinary and extraordinary indices. These pure compound sets of CRI will be used for testing effective medium approximation on Gobi dust for which effective CRI have been also retrieved.</p>

A comparison of modeling approaches for current transport in polysilicon-channel nanowire and macaroni GAA MOSFETs

In this paper, we compare quantitatively the results obtained from the numerical simulation of current transport in polysilicon-channel MOSFETs under different modeling assumptions typically adopted to reproduce the basic physics of the devices, including the effective medium approximation and the description of polysilicon as the haphazard ensemble of monocrystalline silicon grains separated by highly defective grain boundaries. In the latter case, both pure drift-diffusion transport and a mix of intra-grain drift-diffusion and inter-grain thermionic emission are considered. Interest is focused on cylindrical nanowire and macaroni gate-all-around structures, due to their relevance in the field of 3-Dimensional NAND Flash memories, focusing not only on the average behavior but also on the variability in the electrical characteristics of the devices.