Optics and Spectroscopy最新文献

The possibility of complete absorption of an incident electromagnetic wave in a narrow frequency band by a two-dimensional array of metal nanoparticles placed in the surface layer of a one-dimensional photonic crystal structure is demonstrated. The nature of the influence of the parameters of an array of nanoparticles (particle shape, interparticle distance) on the reflection and absorption spectra of the photonic structure in the photonic band gap is determined.

In this work, laser spectroscopy was used to study reverse microemulsions, in which the reaction of ZnS nanoparticle synthesis was carried out. The sizes of the synthesized nanoparticles do not exceed 5 nm. As a result of studying the processes in the reaction medium, it was found that the band of stretching vibrations of HS^– ions in the region of 2568 cm^–1 is an identification sign of the synthesis of nanoparticles: by its intensity it is possible to determine the stage and completion of the ZnS synthesis.

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.