Optics and Spectroscopy最新文献

A method is proposed for separately determining the concentrations of “light” and “heavy” electrons in n-GaSb. It is based on the analysis of reflection spectra in the far infrared region, taking into account the plasmon-phonon coupling. Calibration curves have been calculated that allow one to determine the concentrations of “light” and “heavy” electrons in GaSb using the frequency of high-energy coupled plasmon-phonon mode. For a series of n-GaSb samples the reflection spectra were measured and the concentrations of “light” and “heavy” electrons were determined at room temperature. Electrophysical Van der Paw measurements have been performed on the same samples at room temperature. By comparing the optical and Hall data, the ratios of the mobilities of “light” and “heavy” electrons (parameter b) were determined. This method of determining the value of the parameter b is used for the first time.

The analytical structure and absolute values of the doubly differential cross section of the Compton scattering of two X-ray photons by a multicharged neon-like atomic ion are theoretically predicted.

The features of photoluminescence (PL) of hybrid nanostructures based on InP/InAsP/InP nanowires array with deposited colloidal CdSe/ZnS-trioctylphosphine oxide quantum dots at increasing pump power have been studied. Pumping was carried out by 10 ps laser pulses duration with 1 MHz repetition rate at 532 nm wavelength in the quasi-resonant region of QDs absorption. It has been established, that PL maximum of the nanostructure shifts hypsochromically with increasing of laser power, revealing a gradual dominance of the bands of its components. This PL manifestation is explained by the cascade filling of excited excitonic states, accompanied by the Auger recombination processes and light quenching. The role of free carriers absorption and energy exchange between excitonic states at high pump intensities is noted, as well as a sharp PL duration reduction associated with an increase of stimulated processes in absorption.

The transformation of the graphene-containing optical spectra photonic-crystal structure with a change in the chemical potential (μ) of graphene is studied. In the period of the structure, one layer is a graphene-containing periodic medium (SiO₂/Gr)ⁿ, and the second layer is assumed to be made of pure silicon. In the case of unexcited graphene (μ = 0), the absorption in the structure exceeds the reflection and transmission for frequencies outside the photonic band gaps. Within these zones, most of the incident radiation is reflected, and there is no transmission at all. As μ increases outside the band gaps, the absorption decreases in the low-frequency region, and the transmission increases the stronger, the greater μ. In a structure with an inversion defect inside the band gaps, either suppression or significant rearrangement of the defect mode takes place.

The luminescence spectra of the K₂YF₅:Er³⁺ (0.5 at %) were recorded in the spectral regions of the intermultiplet transitions ⁴I_13/2 → ⁴I_15/2 (region of about 1.5 μm, falling within the transparency window of a standard optical fiber) and ⁴I_11/2 → ⁴I_15/2 (region of about 0.98 μm) with high spectral resolution at different temperatures. Pairs of spectral lines are proposed for the implementation of a Boltzmann luminescent ratiometric cryothermometer in the temperature ranges of about 20, 40, and 60 K with a relative sensitivity of 8 to 3% K^–1. It is shown that measuring the half-width of a luminescence line with a wavelength of 1.538 μm (6500 cm^–1) provides a simple and reliable method for recording temperatures in the range from 20 to 90 K with a relative sensitivity of 3 to 2% K^–1.

A theoretical analysis of a radiation amplifier based on metastable noble gas atoms excited by laser diodes in transverse pumping mode is presented. In the case when the amplified radiation reaches a sufficiently high intensity, the original equations allow a simple analytical solution, from which all the most important characteristics of the amplifier and the optimal parameters of both the working environment and the pump radiation, which ensure the most efficient operation of the amplifier, are easily found.

In this work, the spectra of optical constants of epitaxial layers of cadmium telluride near the fundamental absorption edge are studied. For this purpose, ellipsometric measurements of the layers under study were carried out in a vacuum chamber in the temperature range from T = 38–275°C. A numerical algorithm has been developed for solving the inverse ellipsometry problem for the structures under consideration, with the help of which the spectral dependences of the refractive index n(λ) and absorption index k(λ) are determined in the wavelength range from 700 to 1000 nm. The parametric dependences of k(λ, T) in the fundamental absorption region and in the transparency region are presented. The presence of an extended absorption tail in the transparency region was established, presumably associated with imperfections in the crystal structure.

An experiment was set up to study the afterglow of an extended barrier discharge in low-pressure neon containing Ne⁺, Ne²⁺, and Ne⁺⁺ ions by kinetic spectroscopy. Observation conditions: neon pressure ~0.8–1.7 Torr, electron density in the afterglow stage [e] ~ 10¹¹ cm^–3. In order to compare the rates of collisional-radiative recombination of Ne⁺ and Ne⁺⁺ ions, the effect of pulsed “heating” of decaying plasma electrons by a weak high-frequency field on the intensities of atomic and ion lines was observed. The presented data show that in such a plasma, short-term suppression of recombination processes by electron heating leads to an increase in the brightness of spectral lines in the atomic and ion afterglow spectra, and the reaction of the lines of the latter turns out to be much stronger. Based on simple estimates, it is shown that this effect is due to the difference in the recombination rates of the Ne⁺ and Ne⁺⁺ ions, and this difference turns out to be beyond the scope of theoretical concepts.

Systematic quantum chemical calculations were performed for the ground and a number of low-lying electronically excited doublet and quartet states of the rubidium trimer molecule. The obtained potential energy surfaces (PES), spin-orbit couplings (SOC) and electronic transition dipole moments (ETDM) can be useful for optimizing paths for laser synthesis, cooling and manipulation of stable ensembles of Rb₃ molecules at ultralow temperatures. Ab initio calculations of the electronic structure of the homonuclear Rb₃ molecule, in linear, isosceles triangle and equilateral triangle geometries, were performed using the multi-reference configuration interaction method, taking into account single and double excitations (M-R‑CISD) and with explicit dynamic correlation of only the three valence electrons. The structure of each atom was approximated using a nine-electron effective core potential (ECP28MDF), and molecular orbitals (MOs) were optimized using the spin averaged (over doublet and quartet states) multi-configuration self-consistent field (SA-CASSCF) method. Core–valence correlations between twenty-four subvalence electrons located on doubly occupied MOs and three valence electrons were implicitly taken into account using a one-electron angular momentum-independent Müller–Mayer core polarization potential (CPP). As a result of topological investigations at over 35 000 points, two dimensional PES, SOC, and ETDM functions were obtained and the geometric parameters Rb₃ were found at which the most intense vertical transitions and the maximum influence of the SOC are expected.

In this paper, the possibility of detecting viruses, specifically influenza A virus, based on changes in the spectra of total reflection from macroporous silicon (macro-pSi) films, is demonstrated for the first time. Macro-pSi films with a pore diameter of about 100 nm were produced by electrochemical etching of crystalline silicon substrates. The porosity of the macro-pSi, calculated using the Bruggeman effective medium model, was 75%. Electron microscopy showed that such highly porous films adsorb of 50–100 nm in size viruses on their surface and inside the pores, but the efficiency of adsorption significantly increases when the surface of the nanostructures is functionalized with monoclonal antibodies, providing specific binding of viruses. The reflection spectra of macro-pSi films demonstrate a series of interference fringes, the intensity of which dramatically changes upon virus adsorption. The results obtained demonstrate the possibility of a simple and effective optical method for virus diagnostics using Fabry–Pérot interference in macro‑pSi films.