Laser-induced Shock Compression Research Articles

High-power laser beam shaping using a metasurface for shock excitation and focusing at the microscale.

Achieving high repeatability and efficiency in laser-induced strong shock wave excitation remains a significant technical challenge, as evidenced by the extensive efforts undertaken at large-scale national laboratories to optimize the compression of light element pellets. In this study, we propose and model a novel optical design for generating strong shocks at a tabletop scale. Our approach leverages the spatial and temporal shaping of multiple laser pulses to form concentric laser rings on condensed matter samples. Each laser ring initiates a two-dimensional focusing shock wave that overlaps and converges with preceding shock waves at a central point within the ring. We present preliminary experimental results for a single ring configuration. To enable high-power laser focusing at the micron scale, we demonstrate experimentally the feasibility of employing dielectric metasurfaces with exceptional damage threshold, experimentally determined to be 1.1 J/cm2, as replacements for conventional optics. These metasurfaces enable the creation of pristine, high-fluence laser rings essential for launching stable shock waves in materials. Herein, we showcase results obtained using a water sample, achieving shock pressures in the gigapascal (GPa) range. Our findings provide a promising pathway towards the application of laser-induced strong shock compression in condensed matter at the microscale.

Femtosecond Visualization of hcp-Iron Strength and Plasticity under Shock Compression.

Iron is a key constituent of planets and an important technological material. Here, we combine insitu ultrafast x-ray diffraction with laser-induced shock compression experiments on Fe up to 187(10)GPa and 4070(285)K at 10^{8} s^{-1} in strain rate to study the plasticity of hexagonal-close-packed (hcp)-Fe under extreme loading states. {101[over ¯]2} deformation twinning controls the polycrystalline Fe microstructures and occurs within 1ns, highlighting the fundamental role of twinning in hcp polycrystals deformation at high strain rates. The measured deviatoric stress initially increases to a significant elastic overshoot before the onset of flow, attributed to a slower defect nucleation and mobility. The initial yield strength of materials deformed at high strain rates is thus several times larger than their longer-term flow strength. These observations illustrate how time-resolved ultrafast studies can reveal distinctive plastic behavior in materials under extreme environments.

Evidence of shock-compressed stishovite above 300\u2009GPa

SiO2 is one of the most fundamental constituents in planetary bodies, being an essential building block of major mineral phases in the crust and mantle of terrestrial planets (1–10 ME). Silica at depths greater than 300 km may be present in the form of the rutile-type, high pressure polymorph stishovite (P42/mnm) and its thermodynamic stability is of great interest for understanding the seismic and dynamic structure of planetary interiors. Previous studies on stishovite via static and dynamic (shock) compression techniques are contradictory and the observed differences in the lattice-level response is still not clearly understood. Here, laser-induced shock compression experiments at the LCLS- and SACLA XFEL light-sources elucidate the high-pressure behavior of stishovite on the lattice-level under in situ conditions on the Hugoniot to pressures above 300 GPa. We find stishovite is still (meta-)stable at these conditions, and does not undergo any phase transitions. This contradicts static experiments showing structural transformations to the CaCl2, α-PbO2 and pyrite-type structures. However, rate-limited kinetic hindrance may explain our observations. These results are important to our understanding into the validity of EOS data from nanosecond experiments for geophysical applications.

Time-resolved observation of structural change of copper induced by laser shock using synchrotron radiation with dispersive XAFS

ABSTRACTWe report a single-shot nanosecond time-resolved dispersive XAFS measurement of copper foil under laser-induced shock compression. Obtained EXAFS results indicated clearly the structural evolution, though XANES spectra showed that the laser irradiation does not affect the copper electronic state. The nearest (ca. 0.22 nm) and longer (ca. 0.44 nm) Cu–Cu distances are changed at 4 and 200 ns, respectively, in the radial structure functions (RSFs). It was revealed that an average compression of 2% occurs at 4 ns and is released within 200 ns. It was found that the fragmentation of the copper begins at around 200 ns according to the increase in distance of the RSF.

Influence of strong and weak hydrogen bonds in ices on stimulated Raman scattering.

Stimulated Raman scattering (SRS) in liquid water and ice Ih using Nd:YAG laser is investigated. The spectrum of backward SRS (BSRS) in water is acquired. The spectrum shows an unexpected SRS peak at around 3453 cm(-1) besides the normal peak, which is similar to the spontaneous Raman spectrum of ice VII. The ice VII phase will be formed by laser-induced shock compression in liquid water. Simultaneously, unlike the spontaneous Raman spectrum, the pre-resonance SRS of ice Ih at around 3110 and 3210 cm(-1) is observed. The Raman peaks appeared in liquid water and ice Ih are attributed to the effect of strong and weak hydrogen bonds (H bonds), which should be ubiquitous in other ice phases.

X-Ray Diagnosis of the Pressure Induced Mott Nonmetal-Metal Transition

The evolution of the K-edge x-ray absorption near-edge spectroscopy (XANES) spectrum is investigated for an aluminum plasma expanding from the solid density down to 0.5 g/cm{3}, with temperatures lying from 5 down to 2 eV. The dense plasma is generated by nanosecond laser-induced shock compression. These conditions correspond to the density-temperature region where a metal-nonmetal transition occurs as the density decreases. This transition is directly observed in XANES spectra measurements through the progressive formation of a preedge structure for densities around 1.6 g/cm{3}. Ab initio calculations based on density functional theory and a jellium model have been efficiently tested through direct comparison with the experimental measurements and show that this preedge corresponds to the relocalization of the 3p atomic orbital as the system evolves from a dense plasma toward a partially ionized atomic fluid.

Dislocation density-based modeling of subsurface grain refinement with laser-induced shock compression

Laser shock peening (LSP) is an innovative surface treatment technique applied to improve the mechanical properties and surface microstructures of metallic components. This paper is concerned with prediction of the microstructural evolution of metallic components subjected to single or multiple LSP impacts. A numerical framework is developed to model the evolution of dislocation density and dislocation cell size using a dislocation density-based material model. It is shown that the developed model captures the essential features of the material mechanical behaviors and predicts that the total dislocation density reaches the order of 10 14 m −2 and a minimum dislocation cell size is below 250 nm for LSP of monocrystalline coppers using the laser energy density on the order of 500 GW/cm 2. It is further shown that the model is cable of predicting the material strengthening mechanism in terms of residual stress and microhardness of the LY2 aluminum alloy due to grain refinement in a LSP process with less laser energy densities on the order of several GW/cm 2.

Micro-structuring of CIGS thin-film coated on Mo back contact by ultrafast laser ‘rail-roading’ patterning

We report selective patterning process, laser 'rail-roading' scribing method, of which operating principle is based on transient force balance between the material properties including cohesion and adhesion forces subjected to underlying substrate and laser-induced shock compression and shear forces. By using dual fs-laser beam lines with an interval larger than laser spot size, we provide a proof of the concept by patterning the photovoltaic modules based on CIGS (Cu(In,Ga)Se2) coated on Mo electrode. With varying the interval between the two laser beam tracks, we can provide intact Mo back contact surface without any residues in a manner of more facile, high-speed and high scribing efficiency. We have interpreted the effect of the ambient gases and grooving width on the scribing performance in terms of the cohesion forces between the grains of CIGS thin films as well as adhesion force between underlying Mo layer and CIGS, which are mainly governed by local laser ablation and peening process followed by laser-induced shock compression, respectively.

Shock-induced lattice deformation of CdS single crystal by nanosecond time-resolved Laue diffraction

We report a single-shot nanosecond time-resolved Laue diffraction measurement of cadmium sulfide (CdS) single crystal under laser-induced shock compression. The observed Laue diffraction pattern maintains sixfolding axis of the wurtzite structure for 10ns at a shock pressure of 3.92GPa, which is above the threshold pressure of phase transition to a rocksalt structure. This result shows that a transient wurtzite structure is observed above its threshold pressure to a rocksalt structure on a nanosecond time scale. Uniaxial compression was confirmed by the c∕a value of the transient structure obtained from the (201) and (302) peaks.

On the failure of NiAl bicrystals during laser-induced shock compression

Thin NiAl bicrystals 5 mm in diameter and 150–350 μm thick were tested under laser-induced shock compression to evaluate the material behavior and the effect of localized strain at the grain boundary on the failure of these specimens. Circular NiAl bicrystal samples with random misorientation were grown using a modified Czochralski technique and samples were prepared for shock compression at moderate pressures (<10 GPa). The observed crack patterns on the drive surface as well as the free surface were examined using optical microscopy. Transmission electron microscopy (TEM) of the drive surface as well as in the bulk of one grain was performed on recovered specimens following shock compression. This revealed that a nanocrystalline region with a grain size of 15–20 nm formed on a thin layer at the drive surface following the plasma expansion phase of the laser-induced shock. TEM in the bulk of one grain showed that plastic deformation occurred in a periodic fashion through propagation of dislocation clusters. Cracking on the free surface of the samples revealed a clear grain boundary affected zone (GBAZ) due to scattering of the shock wave and variations in wave speed across the inclined boundary. Damage tended to accumulate in the grain into which the elastic wave refracted. This damage accumulation corresponds well to the regions in which the transmitted waves impinged on the free surface as predicted by elastic scattering models.

Multiscale dislocation dynamics simulations of shock compression in copper single crystal

Ultra short pulse shock wave propagation, plastic deformation and evolution of dislocations in copper single crystals with (0 0 1), (0 1 1) and (1 1 1) orientations are investigated using multiscale dislocation dynamics plasticity analyses. The effects of peak pressure, pulse duration, crystal anisotropy and the nonlinear elastic properties on the interaction between shock wave and dislocations are investigated. The results of our calculations show that the dislocation density has a power law dependence on pressure with a power of 1.70 and that the dislocation density is proportional to pulse duration and sensitive to crystal orientation. These results are in very good agreement with the analytical predications of Meyers et al. [Meyers, M.A., Gregori, F., Kad, B.K., Schneider, M.S., Kalantar, D.H., Remington, B.A., Ravichandran G., Boehly, T., Wark, J., 2003. Laser-induced shock compression of monocrystalline copper: characterization and analysis. Acta Materialia 51, 1211–1228] and the experimental results of Murr [Murr, L.E., 1981. Residual microstructure-mechanical property relationships in shock loaded metals and alloys. In: Meyers, M.A., Murr, L.E. (Eds.), Shock Waves and High Strain Rate Phenomena in Metals. Plenum, New York, pp. 607–673]. It is shown also that incorporating the effect of crystal anisotropy in the elastic properties results in orientation dependent wave speed and peak pressure. The relaxed configurations of dislocation microstructures show the formation of microbands coincident with the slip planes.

Laser-induced shock compression of copper: Orientation and pressure decay effects

Pure copper monocrystals with [001] and [\(\bar 1\)34] orientations were subjected to ultrashort shock pulses ranging in initial duration from 2.5 to 10 ns, induced by a laser at energies ranging from 10 to 70 MJ/m2. The deformation structure was significantly dependent on the crystallographic orientation and depth from the laser-impacted surface, as characterized by transmission electron microscopy (TEM). The threshold pressure for twinning in the [001] direction was observed to be in the range of 20 to 40 GPa compared with 40 to 60 GPa for the [\(\bar 1\)34] orientation. Dislocation densities were also different for the two orientations, under similar shock conditions. The [\(\bar 1\)34] dislocation density was systematically lower. This is attributed to the activation of fewer slip systems resulting in a lower rate of hardening. The different results found for [001] and [\(\bar 1\)34] copper single crystals are described and effects of pressure decay in [\(\bar 1\)34] specimens are discussed. Differences in the mechanical response between the two orientations are responsible for differences in the shear stress in the specimens at the imposed pressures and associated strains. The [\(\bar 1\)34] orientation is initially subjected to deformation by single slip, (111)[101], which has a Schmid factor of 0.4711 and a well-defined easy glide region followed by a cross-slip regime with secondary slip. The [001] orientation has eight slip systems {111}〈110〉 with identical Schmid factors of 0.4082, which lead to immediate work hardening. At an imposed and prescribed pressure (that establishes the strain), the [\(\bar 1\)34] orientation exhibits a lower shear stress. The orientation dependence of the twinning stress is much lower, as expressed by Schmidt factors. This higher stress for [001] predisposes the onset of twinning in this orientation. The results are interpreted in terms of a criterion in which slip and twinning are considered as competing mechanisms. A constitutive description using a modified mechanical threshold stress (MTS) model is applied to the two orientations, incorporating both slip and twinning. The threshold pressure for twinning is calculated, considering the effect of shock heating. The constitutive description provides a rationale for the experimental results: the calculated thresholds are 17 GPa for [001] and 25 GPa for [\(\bar 1\)34].

Equation-of-State Measurements by Laser-Induced Shock Compression: Flyer Acceleration by Laser-Induced Plasmas

Equation-of-State Measurements by Laser-Induced Shock Compression: Flyer Acceleration by Laser-Induced Plasmas

Equation-of-State Measurements by Laser-Induced Shock Compression: Measurement of Equation of State of Tantalum Under Shock-Compressed State

We performed equation of state measurements of tantalum using laser-induced shock waves. A strong shock wave (> TPa) was generated in tantalum by the direct irradiation of laser beams from the GEKKO⁄HIPER glass laser system (laser wavelength λL = 351 nm, laser pulse width τL= 2.5 ns) of the ILE of Osaka University. A two-step, two-materials target, called a double-step target, was used in this experiment. The target assembly was fabricated from a base plate (aluminum or copper), a standard step (aluminum or copper), and a sample step (tantalum). The shock velocity was measured directly by observation of the emission from high temperature material or the change of the reflectivity of the rear surface of the target resulting from the arrival of the shock wave. Particle velocity and pressure were calculated using an impedance-matching technique. The obtained EOS data showed close agreement within the limits of experimental error with the extrapolation of the shock compression curve obtained by the conventional experimental shock technique.

3. Equation-of-State Measurements by Laser-Induced Shock Compression: 3.1 High-Pressure Physics Using Laser-Driven Shocks

High power lasers are nowadays a tool that can be used to determine important parameters in the context of Warm Dense Matter. In this paper, the general issues that have been addressed in the last few years are presented. Recent results concerning water and iron experiments are exposed as a paradigm of laser driven shocks experiments.

Structural transformations in laser shock-loaded quartz

The kinetics of the phase transitions occurring in solid materials under strong compression are an issue of considerable interest, which can be studied using dynamic loading processes. Here, we investigate the phase transformation behavior of quartz under laser-induced shock compression of a very short duration (nanosecond order). Time-resolved measurements, coupled with simple computer simulations, have been used to characterize the pressure pulse induced in the samples. Recovery shots have been performed for postshock spectroscopy, that has revealed permanent structural changes of various types, depending on the experimental conditions (loading pressure, sample thickness, and initial temperature). The results, which differ notably from observations reported under quasi-static compression or longer pulsed loads (microsecond order), suggest a partial amorphization of the shocked samples, as well as the formation of a structure that can be compared to known orthorhombic high-pressure phases. They provide an insight into the early stages of the shock-induced transformation mechanisms in this widely studied material.

Laser-induced shock compression of monocrystalline copper: characterization and analysis

Controlled laser experiments were used to generate ultra-short shock pulses of approximately 5 ns duration in monocrystalline copper specimens with [001] orientation. Transmission electron microscopy revealed features consistent with previous observations of shock-compressed copper, albeit at pulse durations in the μs regime. At pressures of 12 and 20 GPa, the structure consists primarily of dislocation cells; at 40 GPa, twinning and stacking-fault bundles are the principal defect structures; and at a pressure of 55–60 GPa, the structure shows micro-twinning and the effects of thermal recovery (elongated sub-grains). The results suggest that the defect structure is generated at the shock front; the substructures observed are similar to the ones at much larger durations. The dislocation generation is discussed, providing a constitutive description of plastic deformation. It is proposed that thermally activated loop nucleation at the front is the mechanism for dislocation generation. A calculational method for dislocation densities is proposed, based on nucleation of loops at the shock front and their extension due to the residual shear stresses behind the front. Calculated dislocation densities compare favorably with experimentally observed results. It is proposed that simultaneous diffraction by Laue and Bragg of different lattice planes at the shock front can give the strain state and the associated stress level at the front. This enables the calculation of the plastic flow resistance at the imposed strain rate. An estimated strength of 435 MPa is obtained, for a strain rate of 1.3×10 7 s −1. The threshold stress for deformation twinning in shock compression is calculated from the constitutive equations for slip, twinning, and the Swegle–Grady relationship. The calculated threshold pressure for the [001] orientation is 16.3 GPa.

Laser-Induced Shock Compression of Tantalum to 1.7 TPa

An extremely high pressure (1.74±0.22 TPa) was generated in Ta by using strong shock waves driven by direct irradiation of laser beams from the GEKKO XII glass laser system. The shock velocity was measured directly and the particle velocity and pressure were obtained using an impedance-matching technique by considering the intensity profile of the laser beams.