Recent research and development into the formation of nanoscale channels as a central component of nanofluidic biochip systems revolutionized the biological and chemical fields. Exploration of new pathways to form nanochannels is increasingly necessary to provide a new generation of analytical tools with accurate control of liquid fluid flow, high selectivity and increased mass flow rate. Here, we demonstrate that a single 9-keV pulse from X-ray free-electron-laser can form a nanoscale mm-long cavity in LiF. The laser-generated shock pressure results in channel formation with >1,000 length-to-diameter aspect ratio. The development of void is analyzed via continuum and atomistic simulations revealing a sequence of processes leading to the final long cavity structure. This work presents the study of mm-long nanochannel formation by a single high-brilliance X-ray free-electron laser pulse. With MHz repetition rate X-ray free electron laser opens a new avenue for the development of lab-on-chip applications in any material, including those non-transparent to optical lasers.

Studies of the laser-induced ultrafast processes in thin films are of significant importance for the development of microelectronics. These processes include the heating of an electron subsystem, relaxation and transport of the absorbed energy, and generation and propagation of picosecond acoustic waves. In view of this circumstance, to study the dynamics of variation of the differential reflection coefficient ΔR(t)/R0 of a 73-nm-thick Ni film on a glass substrate, pump–probe measurements have been performed in this work with the synchronous detection of a ΔR(t)/R0 signal. High absorbed fluences up to 11 mJ/cm2 have been reached by increasing the pulse-repetition interval tcool of heating (pump) pulses. An increase in tcool makes it possible to better cool the film after heating. As a result, record temperatures Te ≈ 3 kK and Ti ≈ 1 kK and stresses up to 7 GPa have been reached for the first time to the best of our knowledge. These high values have allowed the observation of nonlinear effects for the first time in experiments with synchronous detection.

Sub-picosecond optical laser processing of metals is actively utilized for modification of a heated surface layer. But for deeper modification of different materials a laser in the hard x-ray range is required. Here, we demonstrate that a single 9-keV x-ray pulse from a free-electron laser can form a um-diameter cylindrical cavity with length of ~1 mm in LiF surrounded by shock-transformed material. The plasma-generated shock wave with TPa-level pressure results in damage, melting and polymorphic transformations of any material, including transparent and non-transparent to conventional optical lasers. Moreover, cylindrical shocks can be utilized to obtain a considerable amount of exotic high-pressure polymorphs. Pressure wave propagation in LiF, radial material flow, formation of cracks and voids are analyzed via continuum and atomistic simulations revealing a sequence of processes leading to the final structure with the long cavity. Similar results can be produced with semiconductors and ceramics, which opens a new pathway for development of laser material processing with hard x-ray pulses.

Modification of titanium microstructure after propagation of a melting shock wave (SW) generated by a femtosecond laser pulse is investigated experimentally and analyzed using hydrodynamic and atomistic simulations. Scanning and transmission electron microscopy with analysis of microdiffraction is used to determine the microstructure of modified subsurface layers of titanium. We found that two layers are modified beneath the surface. A top surface polycrystalline layer of nanoscale grains is formed from shock-molten material via rapid crystallization. In a deeper subsurface layer, where the shock-induced melting changes into plastic deformation due to attenuation of SW, the grain structure of solid is considerably affected, which results in a grain size distribution differing from that in the intact titanium. Molecular dynamics simulation of single-crystal titanium reveals that the SW front continues to melt even after its temperature drops below the melting curve Tm(P). The enormous shear stress of ∼12 GPa generated in a narrow SW front leads to free slip of atomic planes, collapse of the crystal lattice, and formation of a supercooled metastable melt. Such melt crystallizes in an unloading tail of SW. The mechanical melting ceases after drop in the shear stress giving rise to the shock-induced plastic deformation. The last process triggers a long-term rearrangement of atomic structures in solid. The overall depth of modified layers is limited by SW attenuation to the Hugoniot elastic limit and can reach several micrometers. The obtained results reveal the basic physical mechanisms of surface hardening of metals by ultrashort laser pulses.

Ultrashort laser pulses with a duration from several to about a thousand optical cycles have significant importance in modern science and engineering. Such a pulse transfers a metal to an excited two-temperature state with hot electrons where the temperature of the electron subsystem T e is much higher than the temperature of the ion subsystem T i . The thermal conductivity in such systems differs from well-known reference values. The thermal conductivity κ and the energy exchange rate between the electron and ion subsystems α are the key parameters of the two-temperature model, which are still poorly studied, although studies of these parameters, particularly α, are numerous. New theoretical and experimental results that make it possible to determine the parameters κ and α for gold have been reported in this work.

Laser-assisted nanostructuring of silicon interfaces provides a unique procedure for leading-edge technologies. We report on a new embossing technique with tightly focused Gaussian-shaped ultrashort laser pulses near the ablation threshold in liquid. We take advantage of a primary microbubble for controllable spatial-modulation of light intensity of succeeding pulses. Such a bubble, generated in liquid near the molten silicon surface by the first pulse, serves as an obstacle for the second pulse following with a sub-millisecond time delay, to produce a diffraction ring pattern. Variation of laser intensity can be utilized to guide the diffraction patterns. Thus the various annular patterns deeply embossed up to hundreds nanometers on the surface are produced with high reproducibility. Morphology of modified surface layer is investigated in detail using atomic-force microscopy, as well as scanning and transmission electron microscopies. Full-wave EM modeling of laser beam diffraction by the bubbles with various radii and shapes shows that the peak intensity in silicon is up to 1.7 times higher than in bubble-free liquid. Atomistic simulation of ultrafast heating with such a diffraction peak reveals that an annular microdimple surrounded by rims is formed by high-gradient pressure in molten silicon to be frozen after several nanoseconds.

Ультракороткие лазерные воздействия с длительностью от нескольких до порядка 1000 световых осцилляций имеют огромное значение в современных науке и технике. Такой импульс переводит металл в возбужденное состояние с горячими электронами: двухтемпературное состояние Te ≫ Ti, где Te, Ti - это температуры электронной и ионной подсистем. При этом меняется коэффициент теплопроводностипо сравнению с хорошо известными справочными значениями. Теплопроводность κ и темп обмена энергией между электронной и ионной подсистемами α - это ключевые параметры 2T модели. До сих пор они остаются плохо изученными. Хотя работ, направленных на их исследование, особенно это касается α, много. В настоящей статье представлены новые теоретико-экспериментальные данные, позволяющие определить κ и α на примере с золотом.

Here we demonstrate the results of investigating the damage threshold of a LiF crystal after irradiating it with a sequence of coherent femtosecond pulses using the European X-ray Free Electron Laser (EuXFEL). The laser fluxes on the crystal surface varied in the range ∼ 0.015-13 kJ/cm2 per pulse when irradiated with a sequence of 1-100 pulses (tpulse ∼ 20 fs, Eph = 9 keV). Analysis of the surface of the irradiated crystal using different reading systems allowed the damage areas and the topology of the craters formed to be accurately determined. It was found that the ablation threshold decreases with increasing number of X-ray pulses, while the depth of the formed craters increases non-linearly and reaches several hundred nanometers. The obtained results have been compared with data already available in the literature for nano- and picosecond pulses from lasers in the soft X-ray/VUV and optical ranges. A failure model of lithium fluoride is developed and verified with simulation of material damage under single-pulse irradiation. The obtained damage threshold is in reasonably good agreement with the experimentally measured one.

The temporal dynamics of the change in the thermally-induced induced reflection coefficient of polycrystalline gold, aluminum, and molybdenum at a wavelength of 800 nm as a result of exposure to a femtosecond laser pulse (at a wavelength of 400 nm) with an intensity of up to 0.2 TW in the in the picosecond time range is studied using pump-probe optical scheme with phase-sensitive detection. New experimental data are obtained on the change in the reflection coefficient under strongly nonequilibrium conditions when the electron subsystem is heated to temperatures of 10 kK, which are relevant for the development of the experimental base for numerical simulation.

Understanding the behavior of matter at extreme pressures of the order of a megabar (Mbar) is essential to gain insight into various physical phenomena at macroscales—the formation of planets, young stars, and the cores of super-Earths, and at microscales—damage to ceramic materials and high-pressure plastic transformation and phase transitions in solids. Under dynamic compression of solids up to Mbar pressures, even a solid with high strength exhibits plastic properties, causing the induced shock wave to split in two: an elastic precursor and a plastic shock wave. This phenomenon is described by theoretical models based on indirect measurements of material response. The advent of x-ray free-electron lasers (XFELs) has made it possible to use their ultrashort pulses for direct observations of the propagation of shock waves in solid materials by the method of phase-contrast radiography. However, there is still a lack of comprehensive data for verification of theoretical models of different solids. Here, we present the results of an experiment in which the evolution of the coupled elastic–plastic wave structure in diamond was directly observed and studied with submicrometer spatial resolution, using the unique capabilities of the x-ray free-electron laser (XFEL). The direct measurements allowed, for the first time, the fitting and validation of the 2D failure model for diamond in the range of several Mbar. Our experimental approach opens new possibilities for the direct verification and construction of equations of state of matter in the ultra-high-stress range, which are relevant to solving a variety of problems in high-energy-density physics.

Evolution of wavefront geometry during propagation and attenuation of initially planar shock waves generated by femtosecond laser pulses in aluminum is studied. We demonstrate that three stages of shock front inflection take place in consistent hydrodynamics and molecular dynamics simulations. During the first stage, the distance traveled by a near-planar wave D-SW(sic)R-L is smaller than the radius of heated laser spot RL. Wave attenuation is associated with one-dimensional plane (1D) rarefaction wave coming from the free surface. Such rarefaction wave shapes the shock wave to a 1D triangular pressure profile along direction normal to target surface with a shock front followed by an unloading tail. The second transitional stage starts after propagation of D-SW ~ R-L, at which the unloading lateral waves begin to arrive to a symmetry axis of flow and initiate inflection of the initially planar shock front. Next at the third stage, the wavefront geometry is finally rounded and rapid attenuation of shock pressure begins at D-SW?R-L. It is shown that such divergent shock wave cannot generate plastic deformations in aluminum shortly after propagation of D-SW ~ R-L. Thus, we may estimate the maximal peening depth as a radius of focal spot, which sets an upper limit for the laser shock peening. The cessation of plastic deformation is caused by the fall of the shockwave amplitude below the elastic limit. In this case, the elastic-plastic wave transitions to a purely elastic mode of propagation. For large-sized light spots, this transition ends in the 1D mode of propagation.

The results of experimental studies of the laser shock waves initiated by a picosecond pulse in iron are presented. Experimental measurements are processed and analyzed using theoretical approaches and numerical simulation. Interest in picosecond actions is caused by uniquely high strain rates, in particular, the dependence of the thresholds of elastoplastic and polymorphic transformations on the strain rate. Investigations are necessary for the development of the field of laser hardening of metals. The first steps in this direction have been taken, although this kind of approach to laser forging hardening is already widely used in practice. Modern developments in the field of shock wave generation and their experimental diagnostics are used, and the related methods of theoretical interpretation of experimental data are being developed. The difficulty lies in the picosecond time scale, since the diagnostics of experiments is limited by kinematics, namely, measuring the coordinates of the free surface. To elucidate the polymorphic transformation kinetics on picosecond time scales, the technique of inverse analysis of the free surface velocity is used for the first time. This technique is validated using the results of hydrodynamic and molecular dynamics simulation with direct extraction of mechanical stresses and strains. A theoretical study of reconstructed free surface velocity profiles by traditional methods confirms the results obtained in the field of their applicability, specifically, on elastic and plastic shock wave fronts. The transformation of iron into the ε phase takes place in the initial region of shock wave propagation, as long as a shock wave has a sufficient amplitude. The cause is a pressure limitation of 40 GPa because of optical breakdown in glass and shock wave attenuation during wave propagation.

Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.

Intense laser radiation leads to irreversible changes in the crystal structure of a target, which are used in laser shock peening technologies. Processes determining the thickness of the residual deformation layer and related residual stresses are studied in this work. It is known that the end of peening is caused by the decaying of the laser shock wave. New information on the transformation of the wave from the elastoplastic to elastic propagation mode under a picosecond impact is obtained. The elastic shock wave is inefficient for peening. The classical configuration with a plastic jump and an elastic precursor ahead of it turns out to disappear during transformation. In this case, the leading edge of the expanding plastic layer gradually decreases its velocity below the bulk velocity of sound, is smeared inside the rarefaction wave, and stops.

Ablation in liquid is numerically simulated with molecular dynamics and hydrodynamics codes. Laser radiation passes through a transparent liquid, illuminates a metal target, and is absorbed in it and reflected from it. The range of absorbed fluences F abs about 1 J/cm 2 is considered, which is of technological interest: the number of nanoparticles formed per laser pulse below these values is small, whereas the optical breakdown of the liquid occurs above them. A theory is developed to estimate the mass and composition of nanoparticles formed by laser radiation using simulation data and thermodynamic information (equation of state of matter).

Elastic-plastic transformations together with or separately of polymorphic phase transitions are important for the theory of shock waves. Here we discuss changing a classification consisting from elastic, split elastic-plastic, and pure plastic shocks. The split shocks means that there are two jumps: the elastic precursor and plastic shock, and that the elastic jump is independent relative to plastic one. In the split regime the precursor moves with elastic speed of sound overrunning the plastic jump and going further and further ahead relative to plastic jump as time proceeds and becoming weaker and weaker. We oppose the split shock to the one-wave (1W) two zones (elastic and plastic—2Z) shock (1W2Z shock). The 1W2Z wave propagates as whole (therefore one-wave), the plastic shock dynamically supports the elastic one, and the average distance between the jumps does not change in time. The powerful elastic shocks (their amplitudes are much higher than are usually suggested for elastic shocks) were found in experiments with femtosecond laser pulses and confirmed in large scale molecular dynamics (MD) simulations. The observation of the 1W2Z shocks is another important finding coming from MD. The report is devoted to lasers, shocks, and applications. In the second part of the report the generation and propagation of the shocks created for laser shock peening by lasers with ultrashort or nanosecond pulses are considered.

Abstract Analytical expressions for the electron thermal conductivity of nickel and aluminum are presented. The thermal conductivity depends on the electronic and ionic temperatures, density and phase of the substance (solid or liquid). The expressions obtained can be used in hydrodynamic calculations of the ablation of these metals or multilayer targets made from them. We consider the case when ablation is caused by the action of ultrashort laser pulses.