Search

Nanoscale periodical chemical composition modification of different two-component compound materials GaAs, CdTe, W0.5C and TiC was realized for the first time through multi-shot femtosecond laser irradiation of their surfaces. The resulting surface modification represents periodical nanoscale ripples with different chemical composition in valleys and ridges. The underlying mechanism is related to a sequence of elementary processes, such as laser excitation surface plasmon-polariton, their interference with the incident laser radiation, inhomogeneous surface heating and incongruent cavitation-like material removal. The latter mechanism is responsible for higher evaporation rate of the components with higher volatility, resulting in growth of surface concentration of low-volatility components.

The NUCLEON satellite experiment is designed to directly investigate the energy spectra of cosmic-ray nuclei and the chemical composition (Z = 1–30) in the energy range of 2–500 TeV. The experimental results are presented, including the energy spectra of different abundant nuclei measured using the new Kinematic Lightweight Energy Meter (KLEM) technique. The primary energy is reconstructed by registration of spatial density of the secondary particles. The particles are generated by the first hadronic inelastic interaction in a carbon target. Then additional particles are produced in a thin tungsten converter, by electromagnetic and hadronic interactions. The deconvolution of spectra was performed. Statistical errors were presented.

The laser-induced damage threshold (LIDT) was measured for a Z n G e P 2 crystal exposed to 0.3–9.5 ps 1030-nm laser pulses. Single-pulse LIDT fluence was ∼ 0.22 J / c m 2 for the laser pulse widths of 0.3–3.5 ps and increased until 0.76 J / c m 2 for 9.5-ps pulses. Multi-pulse LIDT fluence for 0.3-ps pulses at repetition frequencies in the range of 100 Hz–1 kHz was ∼ 0.053 J / c m 2 and decreased further at higher, multi-kHz, pulse repetition frequencies. The coating of the Z n G e P 2 crystal surface with an anti-reflection multi-layer thin film increased the multi-pulse LIDT by one order of magnitude, up to 0.62 J / c m 2 (about 2 T W / c m 2 ). The significant increase in LIDT coupled with a decrease in reflection losses provides a way to cardinally improve efficiency of frequency conversion of popular 1-µm ultrashort pulses into mid- and far-IR ranges with a thin AR-coated Z n G e P 2 crystal sample.

The description of the inhomogeneity of the cosmic ray spectrum in the region of 10 TV, which is observed in experimental data, in terms of isotropic diffusion from a single close source is considered. It is shown that such a description is possible, and the area of possible localization of the source in space and time and its energy are found. The method of penalty functions is used to account for the data on the spectrum of all particles.

The description of the inhomogeneity of the cosmic ray spectrum in the region of 10 TV, which is observed in experimental data, in terms of isotropic diffusion from a single close source is considered. It is shown that such a description is possible, the area of possible localization of the source in space and time, its energy is found. The method of penalty functions is used to account for the data on the spectrum of all particles.The calculation of the anisotropy of the diffusion tensor for the energy range of interest in the galactic magnetic field is also shown.

A correction to this paper has been published: 10.1140/epjd/s10053-021-00234-0

A typical food industry material (stainless steel) was laser-textured to evaluate biofouling of model surface relief. Both initial and laser-textured surfaces were characterized by scanning electron microscopy, energy-dispersive x-ray radiation, Raman spectroscopy, and scanning probe microscopy to reveal the most important pre-requisites for their biofouling by food pathogen bacteria.

Abstract The article discusses the implementation of ultrafast broadband excitation of A-band luminescence of natural diamond by femtosecond-laser pulses with low-energy near-IR photons. Such regime provides A-band luminescence yield with the fourth-power nonlinearity at low laser intensities and second-power nonlinearity at higher laser intensities. These nonlinear dependences of A-band intensity on laser intensity can be related to quasi-resonant four-photon excitation at lower laser intensities and impact excitation of corresponding optical centers at higher intensities, or to similar nonlinear processes in electron–hole plasma relaxing to trapping donor-acceptor centers. Graphic abstract

The NUCLEON experiment is aimed to investigate the composition and energy spectra of high energy cosmic rays. Direct measurements of the energy spectra of cosmic ray protons and nuclei over the range of 1–100 TeV are very important for the solution of a general astrophysical problem of origin of cosmic rays. The satellite was launched on 26 December 2014. The measured charge composition is analyzed and compared with data obtained by other experiments at lower energies. The proton to helium ratio is close to constant over the wide magnetic rigidity area (3–100 TV). The charge composition dependence on magnetic rigidity can be explained by means of the single source model.

Tightly focused, highly spatially multiplexed femtosecond laser pulses, coming at sub-MHz repetition rates, were used to mask-less pattern thin plasmonic films film at ultrafast rates, approaching 25 million of microelements per second. For this purpose, the initial pulses were multiplexed by fused silica diffractive optical elements into linear arrays of 31, 51 and 101 circular light spot and then scanned over the films by a galvanometric scanner through a long-focus objective or high-NA aspherical lens. These optical scheme and 5-μJ pulse energy supported the only 31- and 51-beam micro-patterning, with the corresponding aperture, field-of-view and sub-100 nJ energetic limitations for the laser processing of the film. The resulting large (~105–106 holes per array) arrays of micro-holes of variable diameters and periods in thin films of different thickness and diverse plasmonic materials - Ag, Cu, Al and Au-Pd alloy (80%/20%) - were for the first time systematically characterized in the broad IR-range (1.5–25 μm) in terms of plasmonic effects in extraordinary optical transmission, indicating for the increasing wavenumber a smooth transition from the common Bethe-Bouwkamp transmission to its plasmon-enhanced analogue, ending up with common geometrical (wave-guide-like) transmission. Finally, promising label- and luminescence-free laboratory-scale, robust and high-sensitivity sampling of chemicals and biosamples via plasmonic and chemical contributions, uneven and structurally-sensitive regarding different functional groups of the model analyte molecules and band structure of the plasmonic metal, was demonstrated for the large IR-sensing arrays of micro-holes in plasmonic films, with the obvious perspectives for down-scaling of sensing elements for vis-IR surface-enhanced spectroscopies.

The transmission of near infrared femtosecond laser pulses (wavelength of 800 nm) and supercontinuum radiation (300–750 nm) generated by them through a 50-nm gold film immersed in water has been experimentally studied at the power of focused laser radiation in the range of 1–10 GW. An increase in the excitation intensity is accompanied by the blueshift of the edge of the extinction band of the film, which is attributed to the filling of electronic states of the s band with a low density of states caused by two-photon interband transitions from d bands with a high density of states.

A 50-nm-thick alloyed gold-palladium film on a silica substrate was dewetted by 1060-nm/ns laser pulses and characterized by scanning electron microscopy. Optical transmission spectroscopy of the millimeter-sized spot of the dewetted film demonstrates pronounced Fano resonances, typical for large regular arrays of oligomers of plasmonic nanoparticles. The oligomer configuration and almost pure gold composition of the nanoparticles, underlying the spectral Fano resonances, were revealed via numerical simulations with the input electron microscopy visualization and hydrogen absorption tests. The promising application of Fano resonance for simple optical characterization of ordering or packaging parameters in large-scale arrays of deeply sub-wavelength plasmonic and/or dielectric nano-oligomers was proposed.

Femtosecond low-energy Laguerre – Gaussian pulses of tightly focused visible laser radiation were employed for single-pulse ablative nanostructuring of a 50-nm thick gold film. Similar pulses of lower energy were employed for the efficient plasmonic photoluminescence excitation of a rhodamine 6G dye monolayer in the fabricated nanostructures. The consistency between the shape and polarisation symmetries of the low-energy laser beam, on the one hand, and the gold nanostructures produced by the same beam at a high radiation energy, on the other hand, opens the way to consistent nanostructuring and surface-enhanced analytical spectroscopy with the use of nanostructures.

The experimental study of the single-shot 1030-nm femtosecond laser ablation of bulk silicon and silver in air and liquid media (deionized water, isopropyl alcohol) is reported. The main laser ablation mechanisms were studied via analysis of the resulting microcrater surface morphology and elemental composition in single- and multi-shot (number of pulses N = 10, 100) regimes by scanning electron microscopy with a built-in module for energy-dispersive X-ray spectroscopy. It was concluded, that multi-shot ablation in liquids leads to the lesser extent of the processed surface oxidation, than in dry conditions. The monitoring of the ablative plumes dynamics was implemented with the use of time-resolved emission spectroscopy in the non-filamentation regime, corresponding to the formation of nanoparticles without fragmentation of the ablation products. It was demonstrated, that the lifetime of the plume emission in liquid is significantly shorter, than in air: 5 and 15 ns, correspondingly, for silicon, and 10 and 30 ns for silver.

The introduction of a small amount of subwavelength gold nanoparticles (extinction coefficient ∼0.01–1 cm−1) to water allows the efficient control of filamentation owing to nonlinear dissipative losses of a primary ultrashort pump laser pulse and secondary broadband radiation (supercontinuum), because the intrinsic extinction coefficient in the multiple filamentation regime is below 0.04 cm−1. Optical emission and photoacoustic spectroscopy studies have shown that an increase in losses in a colloidal solution sublinearly increases the power of an ultrashort laser pulse for the nonlinear generation of supercontinuum with the same intensity, and it also increases the filamentation threshold near the supercontinuum generation threshold. At the same time, supercontinuum emission is significantly enhanced in the region of plasmon resonance of nanoparticles against the background of broadband nonlinear absorption. The results demonstrate new possibilities of controlling the nonlinear optical characteristics of media for the generation and filamentation of ultrashort light pulses in various spectral ranges.

Metal nanoparticles have attracted much attention due to their unique properties. One of the important aspects is particle size control for the use of their colloids in various applications. Colloidal solutions of silver nanoparticles were generated in water from silver films of variable thickness at different intensities of a nanosecond fiber laser marker (Bulat) on Yb3+ ions and its scanning speeds over the film surfaces in the laser-plasma ablation regime. The obtained colloidal nanoparticles were characterized by scanning electron microscopy, optical transmission spectroscopy, and dynamic light scattering. A monotonic increase in the extinction coefficient and in the size of the colloidal particles was observed as a function of laser intensity and exposure.

The effect of laser pulsewidth, tuned in the range τ = 0.3–10 ps, on infrared (IR) laser ablation (LA) thresholds of bulk gold, silver and silicon in air and in liquid environments (deionized water, isopropyl alcohol (IPA)) was studied in this work. The influence of laser pulsewidth on the morphology and yield of the ejected nanoparticles (NPs), as well as its impact on the efficiency of NP generation, was studied by UV–vis spectral measurement of the extinction coefficient spectra of NP colloids, fabricated by multi-pass ablation of bulk targets in both solvents at different pulse duration values, by analytical disc centrifuge and by high-resolution scanning electron microscopy. The ablation thresholds are raising with the increase of laser pulsewidth, exhibiting sublinear dependences. The extinction coefficient dependence on τ exhibited a non-monotonous character in case of water medium for all materials, and was gradually descending in case of LA in IPA. Additional MD-TTM (molecular dynamics- two-temperature model) modeling was performed for single-shot laser exposition of bulk Au target in air with τ = 0.3 ps and 4 ps, which allowed distinguishing the main mechanisms of the material removal, the formation of NPs, and the observed crater topography. The performed simulations supported the trend on the ablation threshold increase with the increase of laser pulse duration.

Selenium and silicon nanoparticles were obtained by nanosecond laser ablation in distilled water and characterized by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy. The antibacterial properties of their coatings regarding Gram-positive and Gram-negative bacteria were demonstrated. The presence of singlet oxygen and other reactive oxygen species on the surface of the silicon nanoparticles, leading to oxidative damage to bacterial membranes and further death of the bacteria, was considered a possible mechanism of their antibacterial modality.

The transmission of femtosecond laser pulses of the near-infrared range (wavelength of 1030 nm) through nanocrystalline gold films with a variable thickness (15–90 nm) has been experimentally studied for various intensities of laser radiation in the range of 1–10 TW/cm2. A dip in the transmission coefficient at the wave-length of pump pulses at moderate radiation intensities is due to two-photon transitions from d bands with a high density of states to s and p bands with a low density of states and their saturation at higher intensities. The cross section is estimated for two-photon absorption in gold films enhanced by plasmon resonance of gold nanocrystallites at the wavelength of the second harmonic of exciting radiation, which is compared to values for gold films and various plasmon nanostructures known for other spectral ranges.

Using aluminum as an example, ultrafast sub-ablative broad-range (EUV-IR) spectral tuning of surface plasmon resonance in metals by IR femtosecond laser pulses was demonstrated by theoretical modeling of prompt surface optics for strongly photoexcited materials and of their surface plasmon-polariton (SPP) dispersion curves, as well as by experimental multi-shot laser imprinting of surface plasmon-polaritons as large-scale regular surface ripples with minimal sub-diffraction periods down to 200 nm. According to laser-pump self-reflection and charge emission experiments, the key issue in the prompt optical tuning (spectral red-shifting) of EUV surface plasmon resonance in aluminum by the IR laser pulses is related to ultrafast surface charging of its surface via intense electron emission during the laser pump pulse, depleting its surface electron density and simultaneously decreasing its surface/bulk plasma frequencies, at the corresponding negligible surface ablative etching.

The emission of X-ray quanta, neutrons, and charged particles from deuterated structures under X-ray irradiation is studied. Targets (deuterated chemical-vapor-deposited (CVD)-diamond, palladium, zirconium, and titanium) are irradiated with the use of an X-ray tube equipped with a polycapillary lens with an energy of up to 30 keV and an X-ray tube equipped with a collimator with an energy of up to 25 keV. Different types of detectors, such as a multichannel neutron detector based on He-3 counters, a CR-39 plastic track detector, and silicon surface barrier detectors, are used. The emission of neutrons with an energy of above 10 MeV and alpha particles with an energy range of 7–15 MeV is revealed. This result indicates the possibility of stimulating multiparticle fusion reactions between deuterium nuclei in solid deuterated structures. The analysis of X-ray fluorescence spectra demonstrate the existence of “additional” peaks, which cannot be identified by any characteristic X-ray fluorescence line. Their appearance cannot be associated with any known element or diffraction process. The nature of the origination of the “additional” peaks requires special study.

The generation of supercontinuum radiation at the filamentation of femtosecond laser pulses (800 nm) with a supercritical gigawatt peak power in pure water and colloidal solutions of plasmon gold nanoparticles (perturbative regime) has been studied experimentally. After correction to the extinction of the fluid behind a filament, the supercontinuum radiation yields from the active filamentation zone in water (broadband radiation source) and in colloidal solution (broadband radiation source modified by various in situ interactions with nanoparticles) have been compared and analyzed for various peak radiation powers. As a result, the proposed method of ultrafast broadband nonlinear spectroscopy has allowed the observation of effects of the saturated two-photon interband absorption of gold nanoparticles in the spectral range of supercontinuum generation and the enhancement of this generation in the range of plasmon resonance of nanoparticles.

We report on the application of direct femtosecond laser printing for manufacturing periodic nanoantenna structures with various geometry and period, printed on pure or alloyed noble metal films over a silica substrate. By varying applied pulse energy, we have realised a wide range of possible morphologies, from smooth nano-bumps to protruding nanojets with up to 1 μm height, and finally to through microholes. Using several pulse energy levels, we have printed periodic nanojet arrays with periods from 1.75 to 4 μm, and measured their IR reflection spectra. The resonance frequency and magnitude of the resulting absorbance were found to essentially depend on both the periodicity of the arrays and nanojet geometry. We explain these observations by considering nanojet-assisted plasmon excitation running along the nanojets and along the surface, and found a convincing agreement to the experiments. To this end, we have shown that the reported approach is suitable for designing structures with distinct IR resonances, tunable over a range of at least 2–6 μm. Finally, we have also applied direct laser printing to a variety of noble metal alloys, involving gold, silver and palladium in various combinations and compositions, and showed that nanojets can be reliably printed for such alloys, preserving their chemical composition and its homogeneous volumetric distribution.

We report on fabrication of Ag nanoneedles with tailored chirality via direct ns-laser printing with “structured” laser beams, zero-optical-angular momentum spiral-shaped beams with variable intensity profiles as well as the perfect optical vortex (POV) beams having fixed donut-shaped intensity pattern and variable topological charge. The chirality of the laser-printed nanoneedles was found to be efficiently tailored via optimization of the corresponding intensity pattern of the zero-OAM spiral-shaped beam, while the increase of the topological charge of the POV beam was shown to weakly affect the nanoneedle geometry. Our comparative study reveals the key role of the initial surface intensity (temperature) distribution driving the helical movement of the transiently molten metal and directing formation of the nanoneedles with pronounced chirality on the surface of the noble-metal films. The obtained results pave the way toward realization of easy-to-implement scalable technology for the direct laser printing of plasmonic nanoneedles with pronounced and tailored chirality suited for various nanophotonic, chemical and biosensing applications.

We for the first time theoretically predict and experimentally demonstrate that selective, low-threshold excitation and interference between short-wavelength plasmons on silicon surfaces photoexcited by infrared femtosecond laser pulses give rise to appearance of permanent sub-diffraction surface gratings with their periods down to 100 nm, dramatically differing from near-wavelength surface gratings succeeding the common “laser photon-surface polariton” interference. Such selectivity was provided in this work by in situ white-light (supercontinuum) femtosecond source generated in a multi-filamentation regime in a thin water layer atop the silicon surface, supporting high-efficiency excitation and dynamic tracking of the transiently tunable plasmon resonance on silicon surface for its easy, robust and ultimate surface nanopatterning.

Some results of studies of cosmic rays obtained during the NUCLEON space experiment in 2015–2017 are presented. This experiment was intended for direct measurements of the energy spectra and chemical composition of cosmic rays (Z = 1−30) in the energy range 2–500 TeV. Results presented include energy spectra for various abundant nuclei measured using the new Kinematic Lightweight Energy Meter (KLEM). The primary energies are established using the spatial densities of secondary particles produced in inelastic interactions with a carbon target.

Thin nanostructured metal (Au, Ag) films, magnetron-sputtered on semiconductor (n-type Si) substrate under 6 V voltage exposure for 15 min, exhibit high antibacterial effect against the food pathogens S. aureus and P. aeruginosa. Nanostructures were formed by femtosecond laser ablation, resulting in an array of microspots. The observed effect is caused by the emergence of submicron, laterally periodical static electric and magnetic fields, adjacent to the metal film, causing the abrupt voltage drops, which induce the hyperpolarization of the cell membrane and increase its permeability, resulting in the formation of pores (electroporation) in the membrane and the subsequent apoptosis of the bacterial cell. Additional factors, which enhance the antibacterial effect of the studied materials, are the volume convection in the liquid drop with bacterial culture, caused by the moderate heating of the substrate to 45 °C–50 °C during the electric current flow and electro-taxis of bacteria to the charged nanostructured metal film.

Single-shot nanosecond laser ablation of stainless steel and copper surfaces in ambient air and liquid water environment was studied by contact broadband ultrasonics in the important laser intensity range of 6–450 GW/cm2, covering both regimes of surface phase explosion and formation of sub-critical ablative plasma via optical breakdown in the corresponding dense ablative plume. Similar dependences of ablative plasma pressure were obtained for the dry and wet ablation conditions, differing in their ultrasonic pulse amplitudes by the factor ∼5 and in their pulsewidths by the factor of 1.3 (copper) and 1.6 (steel) for the wet ablation because of the dynamic water-confinement effect. Excepting the confinement effect, these results indicate the similar conditions for pressure generation via sub-critical plasma formation both for the air and water environments, enlightening promising applications of laser ablation for liquid-assisted laser peening and generation of nanoparticles in liquids.

Ultrafast heating of photoionized free electrons by high-numerical-aperture (0.25–0.65) focused visible-range ultrashort laser pulses provides their resonant impact trapping into intra-gap electronic states of point defect centers in a natural IaA/B diamond with a high concentration of poorly aggregated nitrogen impurity atoms. This excites fine-structured, broadband (UV-near-infrared) polychromatic luminescence of the centers over the entire bandgap. The observed luminescence spectra revealed substitutional nitrogen interaction with non-equilibrium intrinsic carbon vacancies, produced simultaneously as Frenkel “vacancy-interstitial” pairs during the laser exposure.

In the present work, we studied the catalytic performance of an oil-soluble nickel-based catalyst during aquathermolysis of oil-saturated crushed cores from Boca de Jaruco extra-heavy oil field. The decomposition of nickel tallate and some aspects of in-situ transformation of the given catalyst precursor under the steam injection conditions were investigated in a high-pressure batch reactor using XRD and SEM analysis methods. The changes in physical and chemical properties of core extracts after the catalytic aquathermolysis process with various duration were studied using gas chromatography for analyzing gas products, SARA analysis, GC-MS of saturated and aromatic fractions, FT-IR spectrometer, elemental analysis, and matrix-activated laser desorption/ionization (MALDI). The results showed that nickel tallate in the presence of oil-saturated crushed core under the injection of steam at 300 °C transforms mainly into nonstoichiometric forms of nickel sulfide. According to the SEM images, the size of nickel sulfide particles was in the range of 80–100 nm. The behavior of main catalytic aquathermolysis gas products such as CH4, CO2, H2S, and H2 depending on the duration of the process was analyzed. The catalytic upgrading at 300 °C provided decrease in the content of resins and asphaltenes, and increase in saturated hydrocarbon content. Moreover, the content of low-molecular alkanes, which were not detected before the catalytic aquathermolysis process, dramatically increased in saturates fraction after catalytic aquathermolysis reactions. In addition, the aromatics hydrocarbons saturated with high molecular weight polycyclic aromatic compounds—isomers of benzo(a)fluorine, which were initially concentrated in resins and asphaltenes. Nickel sulfide showed a good performance in desulfurization of high-molecular components of extra-heavy oil. The cracking of the weak C–S bonds, which mainly concentrated in resins and asphaltenes, ring-opening reactions, detachment of alkyl substitutes from asphaltenes and inhibition of polymerization reactions in the presence of catalytic complex reduced the average molecular mass of resins (from 871.7 to 523.3 a.m.u.) and asphaltenes (from 1572.7 to 1072.3 a.m.u.). Thus, nickel tallate is a promising catalyst to promote the in-situ upgrading of extra-heavy oil during steam injection techniques.

Abstract Results regarding morphological and compositional changes of bimetallic thin film (BMTF), composed of aluminium (Al) and titanium (Ti) nano-layers, by single fs laser pulses, are presented. Laser irradiation was conducted in the air with focused, linearly polarized laser pulses, the duration being 300 fs, wavelength 515 nm, and pulse energy up to $$1.2~\upmu \hbox {J}$$ 1.2 μ J . Effects of the variations of the pulse energy on the changes were studied. In the experiment, single pulse energy values from 0.03 to 0.08 $$\upmu \hbox {J}$$ μ J caused ablation–photomechanical spallation of the upper part of BMTF layer from the Si substrate, without ablation of the whole film. Irradiation at higher pulse energies gradually removed the whole BMTF and even a part of the Si substrate. We explained the influence of different electron–phonon dynamics, in the case of multilayered thin films composed of Al and Ti, on BMTF ablation. Damage/ablation threshold, which is minimal pulse energy/fluence sufficient for starting ablation, was calculated. Graphic abstract

Surface processing of titanium alloy Ti6Al4V samples with nanosecond laser pulses (λ = 1060 nm, τ = 120 ns) under a thin layer of water has been carried out. Changes in the surface topography and structural-phase state of the near-surface layers of the Ti6Al4V alloy are studied by scanning electron microscopy and X-ray diffraction analysis. It is shown that such treatment leads to a refinement of the structure of the surface layer and the formation of tensile residual macrostresses in the near-surface layers.

Results concerning the controllable ablation of nano-layered thin films (NLTF) by femtosecond laser pulses are presented. Investigated samples were titanium-aluminum bilayers, deposited on a silicon substrate, with the top titanium or aluminum layer of variable thickness on the surface. Irradiation was done in ambient air with single femtosecond laser pulses under standard laboratory conditions. The samples were analyzed by complementary methods of optical and scanning electron microscopy and optical profilometry, exhibiting laser-fluence-dependent ablative removal either of the top layer or the entire bilayer or even partial ablation of the underlying silicon substrate. The removal (spallation) threshold fluences for the topmost layer are scalable versus its thickness almost irrespectively of its material, being rather selective for the Ti-coated samples and much less selective for the Al-coated samples. The removal of the entire bilayers was found to be strongly influenced by electronic properties of the underlying metallic layer, dictating the NLTF-Si adhesion, heat conduction, and capacity in the NLTFs toward the NLTF-Si interface and beyond, as well as by their thermophysical characteristics, e.g., almost twice higher melting temperature and enthalpy for Ti. As a result, precise fs-laser machining of the entire NLTFs is pronounced and selective for the samples with the fusible Al at the low-adhesion Al-Si interfaces, compared with the incomplete NLTF removal from the high-adhesion and refractory Ti-Si interfaces.

The aim of the NUCLEON space was to measure spectra of high-energy cosmic rays. The cosmic ray acceleration and propagation processes are determined by the magnetic rigidities of the particles. Thus the magnetic rigidity spectra of cosmic ray carbon and oxygen nuclei obtained by the NUCLEON experiment are analyzed and compared to some other experimental results. The spectral indices calculated for different thresholds with regard to magnetic rigidity are presented. The carbon and oxygen nuclei spectra are steeper than helium nuclei spectra in the 400-10000 GV area. The spectra of carbon and oxygen nuclei are similar to the proton spectrum before the “knee”.

A development of a method for measuring the refractive index of optical media based on the transport-of-intensity equation (TIE) is proposed. The method requires only a complementary metal-oxide semiconductor (CMOS) camera, which registers intensity distributions in several planes. The obtained intensity distributions are used to solve the TIE, known as a non-interferometric and deterministic method of measuring the phase of a light wave. Simple physical relations connecting the phase of the light wave that has passed through an optical medium and its refractive index allows to determine the latter. The results of the experiment confirm the applicability of the proposed method to the problems of optical refractometry.

Laser inscription of form-birefringent nanograting layers inside fused silica by ultrashort (femto-picosecond) laser pulses at 515 nm was studied as a function of laser, average power and pulsewidth in terms of fabrication regimes. Retardance magnitudes were acquired for single birefringent layers inscribed at different laser parameters, enabling fabrication of polarization-based spectral micro-filters in the form of few-layer microdevices and of microfluidic multi-color refractive-index chemo/biosensor.

The formation of alloyed Au/Pd nanoparticles (NPs) from thin magnetron-deposited Au–Pd films by nanosecond laser ablation in water is investigated. The films weight loss dependence is studied by thickness, intensity and laser pulses per point. Prepared NPs are transferred onto the silica wafer and characterized by scanning and transmission electron microscopy as well as optical and energy-dispersive x-ray spectroscopies. NPs size distribution was obtained using the dynamic light scattering (DLS) method.

An exhaustive review on the application of different metal-based nanoparticles for the upgrading of heavy oils has been performed. Particular emphasis has been put on those catalysts used for in-situ upgrading using various thermal treatment methods aiming at extracting heavy oils in a more effective manner. Different types of catalysts have been identified, such as monometallic (Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Ce, and W), non-supported bimetallic (Ti/Zr), non-supported polymetallic (various mixtures of Co, Mo, Ni, W, Al, Zn, Cu), and supported (various metals on silica, alumina, carbon, zeolite, biogenic particles, complex inorganic and organic). Due to the great diversity of nanoparticulated catalysts (type, metal content, synthesis procedure, particle size) and evaluation conditions (experimental setup, reaction conditions, type of feed), it is not possible to make a direct comparison on their performance. Some results are highlighted on the effectiveness of the catalysts for heavy oil upgrading in terms of asphaltene adsorption, viscosity reduction, increase of API gravity, and coke formation. The reviewed literature indicates the need for more research on this topic as to develop more effective catalysts not only for increasing the recovery factor but also for permanent upgrading of the quality of heavy and extra-heavy oil., The work is carried out under the support of the Russian Science Foundation related to the Project N◦ 21-73-30023 dated 17.03.202

This paper investigated the diffraction of a Gaussian laser beam on a binary mask and a refractive axicon. The principles of the formation of a zero-order Bessel beam with sharp drops of the axial field intensity edges were discussed. A laser optical system based on an axicon for the formation of a Bessel beam with quasi-uniform distribution of axial field intensity was proposed. In the laser optical system, the influence of the axicon apex did not affect the output beam. The results of theoretical and experimental studies are presented. It is expected that the research results will have practical application in optical tweezers, imaging systems, as well as laser technologies using high-power radiation.

The interaction of an ultrashort laser pulse of sub-relativistic intensity with an innovative high-average-density targets consisting of numerous sub-microwires or sheets was examined. The research demonstrates the stochastic nature of high-energy electron production in complicated EM field in such targets where volumetric laser energy absorption occurs. The considered laser-target design has a potential for use in compact laser-based neutron sources and warm dense matter research.

A design of high-efficient solid-state source of sub-picosecond ~10-μm wavelength laser pulse is presented. It is based on difference frequency generation in LiGaS 2 nonlinear crystal of ~0.5 μm wavelength laser pulse and its Raman-shifted pulse produced in BaWO 4 crystal. Numerical efficiency of the laser system was estimated to be ~1-2% at experimentally demonstrated efficiency of the Raman shifter ~20%.

A novel, successful method of bactericidal treatment of pathogenic bacterial biofilms in vitro by laser-induced forward transfer of metallic nanoparticles from a polyethylene terephthalate polymeric substrate was suggested. Transferred nanoparticles were characterized by scanning and transmission electron microscopy, energy-dispersive X-ray and Raman spectroscopy. The antibacterial modality of the method was tested on Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas Aeruginosa) bacterial biofilms in vitro, revealing their complete destruction. The proposed simple, cost-effective and potentially mobile biofilm treatment method demonstrated its high and broad bactericidal efficiency.

Here, we report on formation of nanoprotrusions on the surface of a bulk crystalline silicon wafer under femtosecond-laser ablation with a donut-shaped laser beam. By breaking circular symmetry of the irradiating donut-shaped fs-pulse beam, a switch in geometry of the formed surface nanoprotrusions from regular to chiral was demonstrated. The chirality of the obtained Si nanostructures was promoted with an asymmetry degree of the laser beam. An uneven helical flow of laser-melted Si caused by asymmetry of the initial intensity and temperature pattern on the laser-irradiated Si surface explains this phenomenon. Chirality of the formed protrusions was confirmed by visualizing cross-sectional cuts produced by focused ion beam milling as well as Raman activity of these structures probed by circularly polarized light with opposite handedness. Our results open a pathway towards easy-to-implement inexpensive fabrication of chiral all-dielectric nanostructures for advanced nanophotonic applications and sensing of chiral molecules.

Transient stimulated Raman scattering (SRS) of 0.3 ps 515 nm laser pulses in ${\rm BaWO_4}$BaWO

Single microscale filaments were produced in monocrystalline Ia-type diamond by 1030 nm, 300 fs laser pulses tightly focused at NA = 0.3 and different peak powers, visualized by transverse imaging and spectrally characterized by longitudinal micro-spectroscopy, using intrinsic UV A-band photoluminescence (PL) with its peak at about 430 nm. Power-dependent scaling relationships for the local PL yield and diameters of the accompanying luminous micro-channels of recombining electron-hole plasma indicate a transition from three-photon absorption to free-carrier plasma absorption, as the consequent energy deposition mechanisms at increasing peak laser power. Power-dependent elongation of the luminous micro-channels versus peak laser power fitted by a Marburger formula yields, on average a diffraction-based estimate of 0.6 MW critical power for self-focusing within the diamond at the pump laser wavelength of 1030 nm.

We report the possibility of a time-resolved bacterial live/dead dynamics observation with the use of plasmonic nanospikes. Sharp nanospikes, fabricated on a 500-nm thick gold film by laser ablation with the use of 1030-nm femtosecond pulses, were tested as potential elements for antibacterial surfaces and plasmonic luminescence sensors. Staphylococcus aureus bacteria were stained by a live/dead viability kit, with the dead microorganisms acquiring the red colour, caused by the penetration of the luminescent dye propidium iodide through the damaged cell membrane. Photoluminescence was pumped by 515-nm femtosecond laser pulses with linear (Gaussian beam), circular, azimuthal and radial (Laguerre&ndash, Gaussian beam) polarizations, exciting the transverse plasmon resonance of the nanospikes and their apex lightning-rod near-field. According to the numerical electrodynamic modeling, the observed strong increase in the photoluminescence yield for radial polarization, while slightly lower for circular and azimuthal polarizations, compared with the low luminescence intensities for the linear laser polarization, was related to their different laser&ndash, nanospike coupling efficiencies.

In this work, single-shot craters were produced by femtosecond laser ablation using an objective with a numerical aperture NA = 0.25 and laser pulses with the 0.3-ps width and the central wavelength of 515 nm. Ablation was performed in air and distilled water. A sample, 65-nm thick silver film, was prepared by magnetron sputtering onto silica glass and crystalline silicon substrates. Craters were visualized by a scanning electron microscope. Some differences were found in the morphology of craters, depending on the substrate and on the ambient medium. A drastic increase in the crater size was observed during the ablation in water, which is explained by filamentation that occurs when the peak pulse power exceeds 1.3 MW.

Peculiarities of supercontinuum emission generated by sub-picosecond near-IR laser pulses in BaWO4 crystal was experimentally studied. Nonlinear effects contributing to the output spectrum are discussed. Stimulated Raman scattering self-seeded by self-phase modulation emission was observed.