Volume 81, Nº 12 (2017)

A technique for the laser coloration of precious metals is described that is based on the oxidation of a titanium film deposited on the surface of a metal. When laser radiation acts on the film, it is heated and oxidizes. Depending on the radiation parameters, the resulting oxide films have different thicknesses and, due to light interference, they acquire different colors. The visible color of the surface depends on the angle of viewing after imaging. The aim of this work is to identify the color palette of a gold plate’s surface with a thin film of titanium deposited on it. The titanium film is oxidized via fiber laser irradiation with a wavelength of 1.064 μm. Samples of color palettes are examined spectrophotometrically, and the chemical and mechanical stability of the resulting oxide coatings are tested.

Gold nanoparticles are synthesized via laser ablation of a gold target in a liquid. The constants that characterize the efficiency of porphyrins and fullerenes bonding with gold nanoparticles are determined using a modified Stern–Volmer equation. The results from luminescence quenching measurements are presented. It is found that the efficiency of bonding depends on whether there are functional groups in the molecular fragments. Porphyrin containing para-bromphenyl groups at the meso positions of the porphyrin core has the highest affinity for the surfaces of gold nanoparticles.

The possibility of controlling the functional properties of nanostructured thin films deposited on solid substrates using lasers stems from the different topology and elemental composition of the deposited materials. Quantum-correlated states that emerge in the deposited granular nanocluster semiconductor/ metal structures lead to hopping/tunneling conductivity. The possibility of high-temperature superconductivity in such nanocluster structures that are both stable and can give rise to different (nonphonon) electron pairing mechanisms is discussed. An increase in electrical conductivity (by several orders of magnitude) is observed in experiments, depending on the surface and boundary conditions in various topologically organized cluster systems. The problem is to find the optimum numerical relations between the topological parameters in order to obtain the patterns of directivity (such as the Bragg resonance) needed for a sharp increase in electrical conductivity in selective directions.

The current-voltage relationships of deposited structures are measured for cluster structures consisting of nanoparticles of lead telluride. Variation in the value of the tunnel current is shown. Optimum conditions for the possible emergence of quantum-hopping conductivity due to carrier tunneling (the characteristic sizes of the nanoclusters and the distances between them) are determined.

Tungsten surface nanostructuring is performed using the radiation of a Yb:KGW femtosecond laser in air and in liquid nitrogen. Arrays of linear nanostructures and nanorods of tungsten and tungsten nitride are fabricated on the surfaces of targets. Possible scenarios of transforming surface nanostructures of one type into another and the formation of network-like relief are considered.

Results are presented from experimental studies of the filamentation of femtosecond laser radiation in a transparent medium. Schemes for registering plasma channels of filaments, conical emission, and the spatial distribution of radiation intensity are provided. The results from laser action on a target of stainless steel in the multiple filamentation mode.

Using the atomic density matrix formalism, we investigate the dynamic regime of formation of the error signal for resonances of coherent population trapping excited in a three-level Λ-system by a bichromatic field. The optimal parameters of harmonic modulation used in the frequency locked loop are determined with allowance for low-frequency noise.

The interaction between two-level media and a polychromatic field is considered in the limit of small field amplitudes. The obtained third-order corrections allow us to describe a nonlinear response to the field and intermodal interaction. The obtained polarization spectra are compared to numerical solutions to the density matrix equation in the rotating wave approximation. The results can be used in nonlinear comb spectroscopy.

A means of nonlinear interferential comb spectroscopy with increased sensitivity is propsed. Radiation from the comb-generator of a femtosecond laser is focused at the center of a cell with vapors of rubidium atoms, mounted in an arm of a Michelson interferometer. This technique is an improvement of Rozhdestvenski hooks method, with digital registration by the detectors on a CCD array being substituted for the photographic registration of interferograms, resulting in increased interferometric sensitivity (holographic interferometry). A primary spectrogram is processed in digital form on a dual-beam interferometer equipped with a phase modulator to improve sensitivity with the possibility of an a posteriori increase in interferometric sensitivity. Dispersive signals appear in the interferogram spectrogram on two-photon absorption lines when the pumping radiation is focused at the center of a cell with Rb vapors. Nonlinear processes of coherent radiation due to nonlinear interference effects are studied. Numerical simulations are performed that confirm the proposed theoretical model.

An experimental and theoretical study is performed for features of the electronic spectrum of CdSe/CdS/ZnS quantum dots incorporated into Langmuir–Blodgett films. Analysis of the investigated samples assesses the state of the first three levels of the electron spectrum for a quantum object. Good qualitative and quantitative agreement is achieved between the experimental results and theoretical estimates. It is shown that the mechanism of the observed field emission current through a quantum dot is described satisfactorily by the Morgulis–Stratton theory under the considered experimental conditions.

Reflectance spectroscopy is used to study exciton scattering caused by phonons, nonradiative excitons, and free carriers in a heterostructure with a wide (In,Ga)As/GaAs quantum well. Nonradiative excitons and free carriers are created via additional monochromatic illumination by a tunable laser. Constants of exciton–acoustic phonon and exciton–LO phonon scattering are determined from the temperature variations in the nonradiative broadening of exciton resonances. The excitation spectra of nonradiative broadening reveal sharp resonances associated with exciton–exciton scattering and a smooth background caused by exciton–free carrier scattering.

One of the most important features of lead chalcogenides is the narrowing of the energy band gap as the temperature of the crystalline lattice falls, since the energy band gap widens upon cooling for most known semiconductors. For the quantum dots of lead sulfide studied in this work, the point of the first optical transition, which depends on the sample temperature, changes as the size of quantum dots is varied. Such temperature dependences are shown using samples grown in silicate glass with different average sizes of quantum dots.

Terahertz wave propagation in thin semi-insulating GaAs plates is studied by means of timedomain terahertz spectroscopy. It is found that when terahertz radiation is focused on the edge of a crystal plate, a series of several additional pulses is detected ahead of the pulse transmitted through the plate. It is assumed the additional pulses correspond to the surface waves created by radiation reflected once or several times from the side surfaces of the plate. Additional illumination of the sample in the spectral range of impurity-related absorption weakens the terahertz radiation in the crystal, which is experimentally observed as the attenuation of additional pulses.

The formation of surface plasmon–polariton pulses excited in a waveguide spaser during the collective decay of quantum dot excitons distributed in a dielectric layer near a metallic surface is considered. The waveguide spaser’s physical parameters and regimes of generation suitable for the formation of sub-picosecond plasmon–polariton pulses are determined with allowance for dissipative effects in the considered system.

A new approach is proposed for the nondestructive piezoresponse measuring of soft, loose, and fragile nanostructures with simultaneous characterization of their mechanical properties. The new mode is based on HybriD mode atomic force microscopy (fast force–distance curve measurements with real-time processing of the obtained data). The piezoelectric and mechanical properties of diphenylalanine peptide tubes with diameters of less than 100 nm are measured for the first time.