High-intensity Laser Radiation Research Articles

Surface behavior of 16Cr3Al ODS steel—Effects of high laser intensity 1014 W/cm2 in ambiences of air, helium and vacuum

The behavior of 16Cr3Al ODS steel (oxide dispersion strengthened steel), widely employed structural fusion material, under high-intensity laser radiation with intensity up to 1014 W/cm2 was investigated in air, helium and vacuum surrounding. Employed system was 65 fs laser at 804 nm, with applied pulse energy up to 5.25 mJ. Morphological effects were studied – cracking, crater parameters (depth, cross-section), LIPSS (laser-induced periodic surface structures) formation at the crater periphery, hydrodynamic effects, as well as chemical variations on the surface. Ablation thresholds were also determined for all three ambiences (for 100 applied pulses), and they were 0.30 J/cm2, 0.23 J/cm2 and 0.39 J/cm2 in air, helium and vacuum, respectively. Plasma occurred in all experiments and it was most prominent in vacuum due to strongest laser-material coupling.

Tensile strength prediction of orthogonal CFRP under high intensity CW laser irradiation

Considering the two most important factors, delamination and tensile strength temperature dependence, a tensile strength prediction model for orthogonal carbon fiber reinforced polymer (CFRP) under continuous wave (CW) laser irradiation is proposed. In the prediction model, delamination was judged by the thermal data recorded by a thermal imager. In order to eliminate the influence of heating rate on the tensile strength temperature dependence parameters, a two-sided laser irradiation method was proposed to test the tensile strength temperature dependence of CFRP. Furthermore, according to the temperature distribution in the thickness direction of the T700/E44 CFRP specimen and the tensile strength temperature dependence, the tensile strength for orthogonal CFRP under CW laser irradiation was calculated. The results show that the prediction model can reflect the decreasing process of tensile strength with laser irradiation, especially in the cases of high intensity laser irradiation and high tensile load. This research can make a reference for the tensile strength prediction of composite materials in high intensity CW laser irradiation and pre-tension loading conditions.

Ultra-broad band and tunable optical limiting based on photo-refraction of PbSe quantum dots

Optical limiting devices are critical in protecting optical sensors and the human eye from irreversible damage, which block high-intensity laser radiation while allowing low-intensity laser radiation. Basically, there are three types of optical limiters based on absorption, refraction and scattering. Absorption-based optical limiters may be more easily damaged than refraction-based ones due to absorbing high energy. Scattering-based optical limiting effect is relatively weak when the particle size is small. In this paper we report a PbSe quantum dots-based optical limiter, which refracts lights off the transmission path to achieve optical limiting. The nonlinear refractive indices and thermo-optic coefficients of PbSe quantum dots-doped films with different doping concentrations at 405 nm were obtained by using the Z-scan technique. As increasing the input light radiation the refractive index of the doping sample decreases, which makes light beam more divergent and keeps the remaining light intensity stable. As of that PbSe quantum dot has wide-band absorption, the PbSe quantum dot-based optical limiter works from blue to near-infrared. By changing the doping concentration the optical limiting effect could also be adjusted.

Modulating non-linear optical absorption through controlled graphitization of carbon nanostructures containing Fe3C-graphite core-shell nanoparticles

Carbonaceous materials containing Fe/Fe3C(core)-graphite(shell) nanoparticles-embedded carbon globules and carbon nanotubes are synthesized using pyrolysis. The thickness of the graphitic shell on the Fe/Fe3C nanoparticles was varied by exposing Fe-acetylacetonate and toluene precursors to different initial temperatures (reaction tube insertion temperatures) Tin. Furthermore, the thickness of the graphitic layer and the degree of graphitization along with the defect concentration in the graphitic layer was controlled by this process. A proposed mechanism for the formation of such carbonaceous nanostructures due to variation of Tin is provided. Non-linear absorption (NLA) experiments were carried out to explore the effect of graphitization and the role of defects on the laser intensity dependent NLA behaviour of these samples. We demonstrate that degree of graphitization and defect concentration in the highly graphitized layers considerably enhances the NLA behaviour of high intensity laser radiation in the material. The enhancement of NLA coefficient is mainly attributed to the excited state absorption (ESA) and free carrier absorption (FCA) processes. Our results emphasize that the reported carbonaceous materials with optimum amount of defects in the graphitized framework are attractive for optical limiting in laser safety applications.

Surface-Plasmon-Assisted Cooper Pair Formation in Ordered Gold Films at Room Temperature

Electron emission induced by surface plasmon polaritons (SPPs) or simply surface plasmons excited by high-intensity femtosecond laser irradiation of an ordered Au surface has been studied by time-of-flight (TOF) analysis of the emitted electrons. Significant differences have been found compared to the same analysis of smooth surfaces. The SPP field enhancement has been significantly increased in hot spots which have the same periodicity as the surface. In addition to the increased field enhancement, periodic narrow peaks have been detected in the TOF spectrum. In the laser intensity range, where the high-energy peak is present, some of (also periodic in time) less frequent narrow peaks are about twice as large as the remaining ones, indicating the detection of two electrons (Cooper pairs) at about the same time, namely within the resolution of the TOF spectrometer.

The lower limits of the fast ionization waves velocity in a high-intensity laser radiation field

The kinetic processes before the front of an ionizing wave in a gas are investigated. The lower limits of the propagation velocity of a plane ionization wave in the field of high-intensity laser radiation are determined. The results of calculations of the lower boundaries of the velocity of fast ionization waves in argon in the field of a CO2-laser are given. The calculation results are compared with experimental data and other theories.

The Possibility of Obtaining Products from Melted Hafnium Carbide by Treating a Hafnium/Carbon Mechanical Composite with a High-Intensity Photon Flux

A study is performed on the possibility of obtaining products from molten hafnium carbide, the most refractory material known so far, by heating a hafnium/carbon mechanocomposite with high-intensity laser radiation.

Status of laser transformation hardening of steel and its alloys: a review

The state of laser transformation hardening in surface modification of steel and its alloys is reported in this review paper. The laser hardening process involves the use of high-intensity laser radiation to heat the surface of steel into the austenitic region rapidly. Due to high rates of heat transfer, steep temperature gradients result in rapid cooling by conduction. This causes the transformation from an austenite to a martensite microstructure without the need for external quenching and generates a hard wear-resistant surface. The introduction of high-power lasers, such as neodymium-doped yttrium aluminum garnet (Nd:YAG), diode and fiber lasers, has made laser-assisted hardening an attractive candidate for surface hardening processes. Recently, fiber lasers appeared as a competitor to Nd:YAG and diode lasers for material processing. This review paper is a synopsis of the fundamentals of laser hardening, outlining some of its benefits compared with those of conventional hardening techniques and its industrial applications. A selective review of the experimental and numerical research carried out on steel in this area is also presented. Finally, it is concluded that the overall state of research on laser hardening in surface engineering of steel is well developed, and a still-growing industrial application is observed.

Ultrashort and short pulse nonlinear optical investigations in thiolated nine-atom silver quantum clusters embedded in one-dimensional TiO2 nanotube matrix

Nanostructured materials employed as passive nonlinear absorptive limiters offer protection to the human eyes and optical sensors from damage by pulsed laser radiation. However, such materials are prone to laser induced damage, which can be avoided or minimized by employing a robust shell layer. Here, we report the optical limiting properties of nine-atom silver quantum clusters grafted in TiO2 nanotube matrix (Ag9QCs-TNT). Nonlinear absorption revealed from open-aperture Z-scan measurements on Ag9QCs-TNT using both 5 ns (532 nm) and 100 fs (800 nm) laser pulses is larger than those observed from its pristine counterparts (Ag9QCs and TNT). The optical limiting threshold value obtained for Ag9QCs-TNT under fs excitation is smaller by a factor of five compared to that under ns excitation, indicating its ability to passively limit high intensity laser radiation for potential device applications.

A gatling-gun target delivery system for high-intensity laser irradiation experiments

Abstract Intense laser irradiation experiments of sub-micrometer scale targets are currently performed at slow shot rates. This limitation is the result of the inability to place such targets quickly and accurately in the focus of the laser. Here we present a target setup that enables irradiation at a high rate and sub-wavelength positioning accuracy. Three hundred targets were micro-machined and mounted on a single Si wafer. The system implements a closed feedback loop between a triangulation displacement sensor and a motorized manipulator. Using this setup, we demonstrate repeatable stable proton acceleration from 600 nm thick Au foils at a rate of 0.2 Hz. This system will enable studies that require a large overall dose, high statistical significance, or a fine scan of target geometric attributes.

Modulational Instability, Ion-Acoustic Envelope Solitons, and Rogue Waves in Four-Component Plasmas

Modulational instability (MI) of ion-acoustic waves (IAWs) has been theoretically investigated in a plasma system which is composed of inertial warm adiabatic ions, isothermal positrons, and two-temperature super-thermal electrons (cool and hot). A nonlinear Schrodinger equation (NLSE) is derived by using reductive perturbation method that governs the MI of the IAWs. The numerical analysis of the solution of NLSE shows the existence of both stable (dark envelope solitons) and unstable (bright envelope solitons and rogue waves) regimes of IAWs. It is observed that the basic features (viz., stability of the wave profile and MI growth rate) of the IAWs are significantly modified by the superthermality of electrons and related plasma parameters. The results of our present investigation should be useful for understanding different nonlinear phenomena in both space (viz., Saturn’s magnetosphere and interplanetary medium) and laboratory plasmas (viz., hot-cathode discharge and high-intensity laser irradiation).

Formation of channels with changed refractive index at the filamentation of femtosecond laser radiation in quartz glass

The paper considers the phenomenon of filamentation during the propagation of femtosecond laser radiation in transparent solid media as a tool for structuring quartz glasses, contributing to the formation of channels with a modified refractive index. This approach allows changing the intensity distribution in the transverse profile of the laser beam as it passes through the sample. The spatial intensity distribution is determined by the geometry of the formed channels. The use of high-intensity femtosecond laser radiation contributes to the formation of intensity distribution channels.

Study of the potassium bromide surface after laser effects using x-ray photoelectron spectroscopy

The surface of KBr crystals outside and in the crater was examined using an x-ray photoelectron spectrometer (XPS). The comparative analysis of the XPS spectra showed that high-intensity laser irradiation has a significant impact on state and composition of the ionic crystal surface.

First-principles electron dynamics simulation study of high intensity laser irradiation on crystal systems: Photon energy dependent energy transfer

Nonlinear interaction between femtosecond laser pulse and simple dielectric solid, silicon, at an intensity range around the damage threshold has been investigated by first-principles calculations based on time-dependent density functional theory (TDDFT). Intensity and frequency dependences are discussed making comparison with the Keldysh theory.

Laser surface modification of metallic implant materials

Metallic biomaterials are most commonly used as hard-tissue replacements because of their favorable mechanical features and excellent biocompatibility. The objective of this paper is to present an overview of diverse surface modification techniques, with a special emphasis on the laser surface modification method, as well as diverse characterization techniques used for investigating the impact of the surface modification process on metallic implant materials? properties. Moreover, the effect of laser radiation on the surface its and mechanical characteristics, as well as on the structure of metallic bioimplants, is presented. The study of influence of high-intensity laser radiation on metallic materials? surface includes primarily investigations of the surface morphology modifications and specific surface structure formation since their presence enables enhanced osseointegration.

Modulational instability, rogue waves, and envelope solitons in opposite polarity dusty plasmas

Dust-acoustic (DA) waves (DAWs) and their modulational instability (MI) have been investigated theoretically in a plasma system consisting of inertial opposite polarity (positively and negatively) warm adiabatic charged dust grains as well as inertialess non-extensive q−distributed electrons and non-thermal ions. A nonlinear Schrödinger equation (NLSE) is derived by using the reductive perturbation method. It has been observed from the analysis of NLSE that the modulationally stable solitary DAWs give rise to the existence of dark envelope solitons, and that the modulationally unstable solitary DAWs give rise to the existence of bright envelope solitons or rogue structures. It is also observed for the fast mode of DAWs that the basic features (viz. stability of the DAWs, MI, growth rate, amplitude, and width of the DA rogue waves, etc.) are significantly modified by the related plasma parameters (viz. dust masses, dust charge state, non-extensive parameter q, and non-thermal parameter α). The results of our present investigation might be useful for understanding different nonlinear electrostatic phenomena in both space (viz. ionosphere and mesosphere) and laboratory plasmas (viz. high intensity laser irradiation and hot cathode discharge).

Observation of Ultrafast Solid-Density Plasma Dynamics Using Femtosecond X-Ray Pulses from a Free-Electron Laser

The complex physics of the interaction between short pulse high intensity lasers and solids is so far hardly accessible by experiments. As a result of missing experimental capabilities to probe the complex electron dynamics and competing instabilities, this impedes the development of compact laser-based next generation secondary radiation sources, e.g. for tumor therapy [Bulanov2002,ledingham2007], laboratory-astrophysics [Remington1999,Bulanov2015], and fusion [Tabak2014]. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small angle X-ray scattering of femtosecond X-ray free-electron laser pulses facilitates new capabilities for direct in-situ characterization of intense short-pulse laser plasma interaction at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short pulse high intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the pre-inscribed grating, due to plasma expansion, which is an hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.

New approach to the problem of THz generation by intense two-color laser fields

In this paper we propose a new approach to the problem of the generation of electromagnetic radiation of the terahertz bandwidth in nonequilibrium plasma channels created by high-intensity laser radiation in gases. The key idea of the proposed approach consists in superimposing additional amplification to the laser-induced generated THz pulse due to the specific properties of the nonequilibrium plasma channel. We perform a self-consistent analysis of the processes of terahertz pulse formation by the four-wave mixing process and its further propagation and amplification in a nonequilibrium plasma medium in a wakefield of the laser pulse. Optimal parameters for the pump laser pulse and gaseous medium are found for the most efficient conversion of its energy into a terahertz pulse.

Energy transfer dynamics in strongly inhomogeneous hot-dense-matter systems.

Direct measurements of energy transfer across steep density and temperature gradients in a hot-dense-matter system are presented. Hot-dense-plasma conditions were generated by high-intensity laser irradiation of a thin-foil target containing a buried metal layer. Energy transfer to the layer was measured using picosecond time-resolved x-ray emission spectroscopy. The data show two x-ray flashes in time. Fully explicit, coupled particle-in-cell and collisional-radiative atomic kinetics model predictions reproduce these observations, connecting the two x-ray flashes with staged radial energy transfer within the target.

Thermal effect in laser perforation of liver

One of the trends in the development of modern regeneration medicine is the application of high-intensity laser radiation for deep perforation of biological tissues, stimulating the regeneration of structure and functions of the pathologically changed tissues. In the paper, the possibility to control the location and parameters of the biotissue thermal stimulation zones is studied theoretically and experimentally, depending on the conditions of laser perforation in application to the liver laser-induced regeneration problem. The results of numerical simulation revealed the basic trends in the behaviour of the thermal stimulation zone, which are in good agreement with the experimental data on laser perforation of soft biotissues ex vivo using an optical fibre.