Interaction Of Pulses Research Articles

Model of spatial energy distribution in the interaction of counter optical pulses in a fiber

This paper considers the interaction of two high-energy optical pulses of short duration, moving towards each other in the optical fiber. The expected result of the interaction is a structural change in the core, the longitudinal dimensions of which are commensurate with the pulse length. Optical fiber with such a structure can be used as a sensitive element in sensory applications. To solve the problem of pulse interaction, a system of equations describing the propagation of two opposite plane electromagnetic waves in a dielectric waveguide was composed. The calculations were performed in the numerical simulation environment COMSOL Multyphysics. The results show that the calculated spatial distribution has four pronounced centers. A comparison with experimental data is given.

Interplay Between Self-Focusing and Self-Compression of Elliptical q-Gaussian Laser Pulse Interacting with Axially Inhomogeneous Plasma

Interplay Between Self-Focusing and Self-Compression of Elliptical q-Gaussian Laser Pulse Interacting with Axially Inhomogeneous Plasma

Interactions of ultrashort laser pulses with hemoglobin: Photophysical aspects and potential applications

Hemoglobin (Hb), a life-sustaining and highly abundant erythrocyte protein, is not readily fluorescent. A few studies have already reported Two-Photon Excited Fluorescence (TPEF) of Hb, however, the mechanisms through which Hb becomes fluorescent upon interaction with ultrashort laser pulses are not completely understood. Here, we characterized photophysically this interaction on Hb thin film and erythrocytes using fluorescence spectroscopy upon single-photon/two-photon absorption, and UV-VIS single-photon absorption spectroscopy. A gradual increase of the fluorescence intensity, ending up with saturation, is observed upon prolonged exposure of Hb thin layer and erythrocytes to ultrashort laser pulses at 730 nm. When compared to protoporphyrin IX (PpIX) and oxidized Hb by H2O2, TPEF spectra from a thin Hb film and erythrocytes showed good mutual agreement, broad peaking at 550 nm, supporting hemoglobin undergoes degradation and that same fluorescent specie(s) originating from the heme moiety are generated. The uniform square shaped patterns of the fluorescent photoproduct exhibited the same level of the fluorescence intensity even after 12 weeks from the formation, indicating high photoproduct stability. We finally demonstrated the full potential of the formed Hb photoproduct with TPEF scanning microscopy towards spatiotemporally controlled micropatterning in HTF and single human erythrocyte labelling and tracking in the whole blood.

Arbitrary Time Shaping of Broadband Low-Coherence Light Based on Optical Parametric Amplification

Laser–plasma interactions (LPIs) hinder the interaction of high-energy laser pulses with targets. The use of broadband low-coherence light has been proposed to reduce the impact of LPIs. In this study, to improve the time–frequency characteristics of broadband low-coherence optical seeds, we proposed an arbitrary time-shaping technique scheme based on optical parametric amplification (OPA) that differs from traditional arbitrary time shaping. The shaping process and output characteristics were analyzed in detail. The theoretical and experimental results show that an arbitrary time-shaping pulse output with a large time-shaping contrast, fast-rising edge, and wide spectral width can be obtained. The time shaping contrast of the shaped pulse can be >300:1, and the spectral width is ~40 nm. The output time waveform is smoother than in traditional schemes, and the noise-like modulation is approximately 4% (approximately equal to the unshaped initial amplified spontaneous emission source). The arbitrary time-shaping scheme based on OPA provides a viable solution for the temporal waveform shaping of broadband low-coherence light.

Mathematical modeling of experiments on the interaction of a high-power ultraviolet laser pulse with condensed targets

Objectives. The paper aimed to review and analyze the results of works devoted to numerical modeling of experiments on the interaction of high-power ultraviolet (UV) laser pulses with condensed targets. The experiments were carried out at GARPUN, the powerful KrF-laser facility at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences (Moscow). The relevance of the research is related to the use of excimer UV lasers as a driver for a thermonuclear reactor. Physical aspects of laser-plasma interaction, including those related to the possibility of using two-sided cone target in a fission-fusion reactor, are discussed.Methods. The research is based on physico-mathematical models, including Euler and Lagrange.Results. The mathematical modeling of three types of natural experiments is presented: (1) burning through different thicknesses of Al foils by high-power UV laser; (2) studying hydrodynamic instability development at the UV laser acceleration of thin polymer films and features of turbulent zone formation; (3) interaction of high-power UV laser pulses with two-layer targets (Al + Plexiglas) and study of fine structures. Numerical modeling showed that a hybrid reactor with UV laser driver can use targets in the form of two-sided counter cones.Conclusions. Physico-mathematical models are developed along with 2D codes in Lagrangian and Eulerian coordinates as confirmed in the results of natural experiments. The models can be used to describe the physics of high-power UV laser pulses interacting with various targets and forecast the results of reactor-scale experiments.

Interaction of Finite Perturbations with the Front and Singularity of the Profile of a Nonlinear Wave in a Dissipative Medium

The interaction of a short pulse with three types of wave profiles in a nonlinear dissipative medium are described: a stationary shock front of finite width, a nonstationary forming front, and a “stationary” wave the profile of which contains a singularity. Exact solutions to the Burgers equation are used, which describe these interactions, as well as the symmetry properties of this equation.

Enhanced target normal sheath acceleration with a grooved hydrocarbon target

The interaction of a high-intensity ultrashort laser pulse with a few micrometers-thick hydrocarbon target is known to accelerate protons/ions to multi-MeV, on the rear side of the target, via the mechanism of target normal sheath acceleration. Micro-structuring the target front is one of the promising approaches to enhance the cutoff energy as well as to reduce the divergence of accelerated protons/ions. In this paper, the interaction of a normally incident intense laser pulse with targets having single micrometer-sized grooves, at their front side, of semi-circular, triangular, and rectangular shapes has been studied by using two-dimensional particle-in-cell simulations. It is observed that as compared to a flat target for targets with a rectangular groove at the front side the focused hot electron beam at the rear side results in an approximately fourfold increase in the cutoff energy of accelerated protons. For triangular and semi-circular groove targets, the cutoff energy remains comparatively lower (higher than the flat target though). The angular divergence of the accelerated protons/ions is also found to be relatively much lower in the case of a rectangular groove.

Intense laser pulse interaction with a nanofoil and generation of energetic protons in underdense upstream plasma

Intense laser pulse interaction with a nanofoil and generation of energetic protons in underdense upstream plasma

Effective Line X-ray Generation by Chirped Femtosecond Laser Pulses Interaction with Copper Target at Local Helium Flow

Effective Line X-ray Generation by Chirped Femtosecond Laser Pulses Interaction with Copper Target at Local Helium Flow

Betatron Radiation and Bremsstrahlung in the Interaction of Intense Laser Pulse with Solid Target

X-ray generation via synchrotron radiation and bremsstrahlung in the interaction of short laser pulses with a solid target is of much current interest owing to its numerous applications. The efficiency of laser to X-ray energy conversion is thus a crucial factor. We found that the energy conversion efficiency of synchrotron radiation and bremsstrahlung is mainly governed by the ratio of the laser pulse width to the preplasma width, which is in turn governed by the laser profile, intensity, and spot size. Synchrotron radiation dominates when the ratio is less than unity, otherwise bremsstrahlung dominates. The type of radiation can thus be controlled by tailoring the laser parameters.

Argonda Dairesel Polarize Yüksek Harmonikler: Dipol ve Dipol Olmayan Etki

The interaction of the intense laser pulse, which forms the basis of the strong laser field and non-linear optical physics, with atoms, molecules, and solids leads to the High Order Harmonic Generation (HHG). There are many theoretical and experimental research related to this process defined by the Semi-Classic Model which is called the Three Step Model. In this article, the dipole and non-dipole effects specified in the theoretical Lewenstein model to be used in the Argon atom interacting with the strong circular laser field (800nm) and the resulting higher order harmonic spectrum will be investigated. We compared the results obtained using the non-collinear beams with opposite circular polarizations with those obtained using a single circularly polarized beam or a linearly polarized beam. It could be said that the circular polarization can significantly affect the HHG process in an argon atom exposed to a laser field with 800 nm wavelength and 1015 W/cm2 intensity.

Quantum classical approach to spin and charge pumping and the ensuing radiation in terahertz spintronics: Example of the ultrafast light-driven Weyl antiferromagnet Mn3Sn

The interaction of a femtosecond laser pulse with magnetic materials has been intensely studied for more than two decades in order to understand ultrafast demagnetization in single magnetic layers or terahertz emission from their bilayers with nonmagnetic spin-orbit (SO) materials. However, in contrast to well-understood spin and charge pumping by dynamical magnetization in spintronic systems driven by microwaves or current injection, analogous processes in light-driven magnets and radiation emitted by them remain largely unexplained due to the multiscale nature of the problem. Here we develop a multiscale quantum-classical formalism---where conduction electrons are described by quantum master equation (QME) of the Lindblad type, classical dynamics of local magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation, and incoming light is described by classical vector potential, while outgoing electromagnetic radiation is computed using the Jefimenko equations for retarded electric and magnetic fields---and apply it to a bilayer of antiferromagnetic Weyl semimetal ${\mathrm{Mn}}_{3}\mathrm{Sn}$, hosting noncollinear local magnetization, and SO-coupled nonmagnetic material. Our $\mathrm{QME}+\mathrm{LLG}+$Jefimenko scheme makes it possible to understand how a femtosecond laser pulse directly generates spin and charge pumping and electromagnetic radiation by the ${\mathrm{Mn}}_{3}\mathrm{Sn}$ layer, including both odd and even high harmonics (of the pulse center frequency) up to order $n\ensuremath{\le}7$. The directly pumped spin current then exerts spin torque on local magnetization whose dynamics, in turn, pumps additional spin and charge currents radiating in the terahertz range. By switching on and off LLG dynamics and SO couplings, we unravel which microscopic mechanism contributes the most to emitted terahertz radiation---charge pumping by local magnetization of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ in the presence of its own SO coupling is far more important than standardly assumed (for other types of magnetic layers) spin pumping and subsequent spin-to-charge conversion within the adjacent nonmagnetic SO-coupled material.

High-intensity laser pulse interaction with a counter propagating electron beam for terahertz field generation in magnetized plasmas

High-intensity laser pulse interaction with a counter propagating electron beam for terahertz field generation in magnetized plasmas

High-Precision PCB Topologies Formation by Selective Laser Micromachining

The paper considers possibility of using laser radiation to form and correct printed circuit topology boards through micromachining. Processes arising from the interaction of ultrashort laser pulses with processed thin-film coatings are considered. The dependence of the effect of a variable sequence of laser pulses on the quality of the formed holes in coating is presented. Experimental data on the selection of optimal exposure modes of femtosecond radiation on a multilayer coating for selective ablation are presented. Femtosecond laser micromachining allows the precision formation of topological contours, regardless of treated coating type, its thermal and electric conductive properties.

Premium food for offspring? Black-backed Woodpecker (Picoides arcticus) diet during breeding season in eastern Canada

Knowledge on the diet of the Black-backed Woodpecker (Picoides arcticus Swainson, 1832) is fragmentary and relies on a limited number of studies. Gaps remain in our understanding of the plasticity of its diet, particularly in the eastern part of its range. The main objective of this study was to assess the diet of Black-backed Woodpeckers in burned and unburned habitats and among sexes and ages in Québec. We collected feces and fecal bags from unburned and burned habitats in the Central Laurentians ecoregion of the eastern boreal shield ecozone and assessed diets based on identified prey items. Buprestidae and Cerambycidae of the sub-family Lamiinae were the predominant prey for adult Black-backed Woodpeckers in burned habitats, and the Pythidae Pytho niger (Kirby, 1837) and Lamiinae were the most prevalent prey in unburned habitats. Lamiinae were the most predominant prey items provisioned to nestling in burned habitat, while P. niger was their predominant food in unburned habitat, followed by Cerambycidae (without Lamiinae) and Lamiinae. Our results present new insights into Black-backed Woodpecker diet where parents feed their offspring with the largest prey available, potentially providing higher fitness for their offspring. Furthermore, our study confirms that Black-backed Woodpeckers, at least in the eastern part of its range, are not restricted to feed on Lamiinae but are rather opportunistic in taking advantage from resource–pulse interactions provided by recently disturbed habitats, especially from recently burned habitats.

Pulsed laser-induced dewetting to fabricate Au-Pd nanoparticles supported on ZnO films and its application for the photocatalytic degradation of indigo carmine

Gold-palladium (Au-Pd) bimetallic alloy nanoparticles (NPs) were obtained by the interaction of a laser pulse with a stack of Au and Pd thin films, these films were previously and sequentially deposited on a zinc oxide (ZnO) thin films grown on a glass substrate. This method can produce, with a single laser pulse, spherical NPs of different compositions which remain attached to the surface of the ZnO film. X-ray diffraction analysis showed that the NPs are composed of a solid solution of the metals whose relative content was modified by varying the deposition time of the starting metal films. The higher amount of Pd in the NPs, the smaller particle size being the minimum around 50 nm. To demonstrate the usefulness of this method to produce Au-Pd NPs directly on surfaces, the decorated ZnO layers were tested as photocatalysts material for the decomposition of indigo carmine dye. The bimetallic NPs supported on ZnO showed to have a better photocatalytic performance to decompose the dye than their mono-metallic counterpart and bare ZnO thin film. The bimetallic NPs richer in Pd achieved a degradation of 99% of the dye while bare ZnO film reached just 32%.

A new method for predicting the morphology and surface roughness of micro grooves in aluminum alloy ablated by pulsed laser

It is challenging to predict the morphology of the grooves ablated by pulsed laser. To predict the morphology and surface roughness of aluminum alloy grooves at low laser fluence (ranging from 17.68 J/cm2–28.29 J/cm2), a method which combines analytical and simulation approaches is proposed in this research. The proposed method takes into account the evaporation and redeposition behavior, examines the impact of pulse interactions through simulations, and focuses on the influence of molten pool flow on surface roughness. Firstly, the level set method is employed to accurately track the vapor-liquid interface and predict the ablative morphology of a single pulse. Secondly, the influence of molten pool flow on surface morphology in the case of pulse interaction is quantitatively described by comparing the morphology of a two-pulse ablation simulation with scanning speed in the heat source to the morphology obtained by simple superposition of a single pulse, the resulting morphological error is attributed to flow. Finally, the flow deviation of the ablated groove is compensated for applying an analytical method, and the three-dimensional morphology of the ablated groove is calculated by using the proposed expression. The computational analysis using the new method is compared with the experimental results, demonstrating that the average prediction error for contour is less than 7 %, and the error for roughness prediction is less than 10 %. By analyzing the melt flow using the new method, it is discovered that as the laser fluence increases, the range of melt flow expands and the amplitude of vertical flow increases, which results in the increase of surface roughness. Notably, the scanning speed does not directly affect the roughness by influencing the melt flow.

Interaction of Finite Perturbations with the Front and Singularity of the Profile of a Nonlinear Wave in a Dissipative Medium

The interaction of a short pulse with three types of wave profiles in a nonlinear dissipative medium are described: a stationary shock front of finite width, a nonstationary forming front, and a “stationary” wave the profile of which contains a singularity. Exact solutions to the Burgers equation are used, which describe these interactions, as well as the symmetry properties of this equation.

Optoacoustic and optical coherence tomography guided lipid-selective ablation for atherosclerotic plaque

Atherosclerosis is a life-threatening disease of utmost clinical importance, which, despite recent progress in cardiovascular field, is still related to high morbidity and mortality. It is characterized by the accumulation of lipids within the arterial wall that is vulnerable and prone to rupture in pathological cardiovascular changes and acute events. In this paper, for the first time, we proposed a conceptually theranostics method to stabilize the atherosclerosis: Optoacoustic tomography (OAT)/optical coherence tomography (OCT) guided lipid-selective ablation for atherosclerotic plaque. To achieve this theranostics goal, the underlying pulsed laser-tissue interaction mechanisms of OA/OCT theranostics models was investigated for both OAT localization of lipid core as well as pulsed laser power titration for ablation. OCT was used to observe pre- and post-ablation result of fibrous caps and vessel wall, followed by histology validation. The feasibility of OA/OCT was first verified by plaque composition mimicking experiment. Furthermore, ex-vivo mouse aortas containing lipid-rich plaque were imaged and selectively ablated to show the intrinsically registered OA/OCT for targeting lipid core without causing adjacent tissue damage. Our results demonstrated the superiority of this theranostics technique for effective and precise removal of atherosclerotic plaque, which brings new capabilities and photonics insights to cardiovascular medicine.

On the Thermal Behavior during Spatial Anisotropic Femtoseconds Laser-DNA Interaction: The Crucial Role of Hermite Polynomials.

A novel analytical formalism based on the quantum heat transport equation is proposed for the interaction of fs-laser pulses with deoxyribonucleic acid (DNA) strands. The formalism has the intensity of the laser beam and the interaction time between the laser and the DNA as input parameters. To this end, the thermal distribution generated in the irradiated DNA strands was introduced by splitting the laser beam into transverse Hermite-Gauss modes. To achieve this goal, a new powerful mathematical model was developed and applied. Fluctuations in laser intensity were taken into account by modeling them as superpositions of Hermite-Gauss laser modes. These analyses were carried out for a laser pulse duration of 100 fs, where a tiny heat-affected zone is expected, with positive predicted effects on the stability and repeatability of this technology. The main conclusion is that the laser beam spatial distribution intensity plays an essential role in the generation of the shape and magnitude of the thermal field at the junction of the irradiated DNA strands. The model may prove useful in modeling laser beam processing under significant intensity fluctuations. There are at least two main areas of application for the present model of heat transfer from laser to DNA: (i) the study of DNA elongation without destroying the target information (for a sample temperature variation lower than 10 K; in the case of H[1,y]); and (ii) cancer treatment (especially of skin tissue), where we should obtain a temperature variation higher than 10 K (but lower than 30 K; in the case of H[2,y], H[4,y]), in order to eradicate the diseased cells.