Yu. G. Selivanov

Multicomponent fiber-optical gas sensor based on MIR tunable diode lasers

Abstract The presented multichannel system is intended for simultaneous analysis of several components of a gas mixture by using a set of tunable diode lasers (TDL). The design and schematic solution of the sensor is based on the integration of MIR fibers with TDLs and photodetectors kept cold at temperatures from 80 to 120 K. Optical fibers are used in the system for transmitting radiation from the lasers to the multipass analytical cell and then to the IR detectors. The key components of the system are: MBE lead salt heterolasers for the spectral range 3 to 16 μm, A3B5 heterolasers for the spectral range 0.75 to 3.6 μm, polycrystalline fibers from silver halides for the spectral range 4 to 16 μm, chalcogenide glass fibers for the spectral range 1 to 7 μm, and super dry silica fibers for the near IR region 0.75 to 2.5 μm. The presented solution gives a set of new advantages and capabilities: simplicity and dependability of cryogenic systems; ability of using IR laser radiation in areas difficult to access; ability to remote measurements in extreme sterile and clean conditions; correcting for absorption signal of atmospheric air as a contaminant in analysis; smaller in size and lighter multichannel TDL systems.

Molecular beam epitaxy of Pb1 − xEuxTe and Pb1 − xSnxTe layers and related periodic structures

Layers and periodic Bragg structures based on Pb1 − xEuxTe (0 < x < 1) and Pb1 − xSnxTe (0 < x < 0.1) ternary solid solutions have been grown on (111) BaF2 and (111) Si substrates by molecular beam epitaxy. X-ray diffraction measurements show that the layers in three-period EuTe/Pb0.94Eu0.06Te structures maintain the [111] crystallographic orientation normal to the substrate plane. In the interface plane, the [110] directions of the layers and substrate are parallel to each other. The full width at half maximum of the rocking curve of each layer of both the binary and ternary compounds is about 20′. The large optical contrast (40%) in such structures allowed us to reach 99.9% mid-IR reflectivity.

Magnetotransport in thin epitaxial Bi2Se3 films

The magnetoconductivity of thin Bi2Se3 films covered by a protective Se layer and grown at (111) BaF2 substrates is studied. It is shown that the negative magnetoconductivity observed at low magnetic fields and caused by the effect of weak antilocalization, as well as the Shubnikov−de Haas oscillations at higher fields, is determined only by the magnetic field component perpendicular to the film plane. The obtained experimental results can be reasonably interpreted under the assumption that the studied films exhibit two-dimensional topologically protected electron states. Moreover, the contribution of these states to the total conductivity turns out to be the dominant one.

Dispersion of the refractive index of epitaxial Pb1 − xEuxTe (0 ≤ x ≤ 1) alloy layers below the absorption edge

The transmittance spectra of epitaxial Pb1 − xEuxTe (0 ≤x ≤ 0.1) alloy layers are exploited to study the dispersion of their refractive index in the spectral range from 650 to 8000 cm−1 (below the absorption edge). The refractive index and the position of the absorption edge as functions of the composition parameter of the alloys are determined at two temperatures, 80 and 295 K. The refractive index is calculated in the context of the classic wave concepts of propagation of electromagnetic radiation. The experimentally determined dispersion dependences are described by the empiric Sellmeier expression of the second order. From analysis of the transmittance of the layers, it follows that the band gap of the epitaxial Pb1 − xEuxTe alloys increases with increasing temperature at x < 0.5 and decreases at x > 0.5.

Transmission spectra of epitaxial layers of Pb1 − xEuxTe (0 ≤ x ≤ 0.37) solid solutions in the frequency range 7–4000 cm−1

The spectra of epitaxial Pb1 − xEuxTe (0 ≤ x ≤ 0.37) solid solution layers grown on BaF2 and Si substrates have been investigated over a wide frequency range 7–4000 cm−1 at temperatures of 5–300 K. Apart from the phonon and impurity absorption lines, the absorption in a local mode in PbEuTe layers of substrates and buffer layers has been observed in the frequency range 110–114 cm−1. As the temperature decreases from 300 to 5 K, the transverse phonon mode softens from 33.0 to 19.5 cm−1.

Radiative transitions to localized Eu states in Pb1−xEuxTe solid solutions

Two types of radiative transitions were observed in the low-temperature photoluminescence spectra of Pb1−xEuxTe (0 ≤ x ≤ 0.09) solid solutions: an intense line corresponding to the transitions from the conduction to the valence band and a series (up to 15) of narrow lines corresponding to the transitions from the hybridized conduction band to the split Eu3+ levels. The intensity of the discrete lines increases with x, and their energies (and intensities) weakly depend on the temperature. The absorption and emission of the discrete lines are caused by the 4f7(8S7/2) ↔ 4f6(7FJ)[L6− + 5dt2g] transitions.

Structural distortion behind the nematic superconductivity in Sr x Bi2Se3

An archetypical layered topological insulator Bi

Quantum corrections to the conductivity and anisotropy of the magnetoresistance in Eu-doped Bi 2 Se 3 thin films

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Pb1–xEuxTe alloys (0 ⩽ x ⩽ 1) as materials for vertical-cavity surface-emitting lasers in the mid-infrared spectral range of 4–5 μm

Se

Infrared spectroscopy of Bi2Te2Se

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