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Laser ablation propulsion and orbit cleaning are developing areas of research. The general aim of laser-based techniques applied to this field is to maximize the momentum transfer produced by a laser shot. This work presents results from ballistic pendulum experiments under vacuum on aluminum, copper, tin, gold, and porous graphite targets. The work has focused on the metrology of the laser experiments to ensure good stability over a wide range of laser parameters (laser intensity ranging from 4 GW/cm 2 to 8.7 TW/cm 2 , pulse duration from 80 ps to 15 ns, and wavelengths of 528 or 1057 nm). The results presented compile data from three experimental campaigns spanning from 2018 to 2021 on two different laser platforms and using different pulse durations, energies, and wavelengths. The study is complemented by the simulation of the momentum from the mono-dimensional Lagrangian code ESTHER. The first part of this work gives a detailed description of the experimental setup used, the ESTHER code, and the treatment of the simulations. The second part focuses on the experimental results. The third part describes the simulation results and provides a comparison with the experimental data. The last part presents possible improvements for future work on the subject. [ABSTRACT FROM AUTHOR]

Laser-driven shock experiments were conducted at a synchrotron facility to investigate the dynamic response of polyurethane foam. These experiments were coupled to in situ x-ray imaging to radiograph foam deformations and to determine the propagation velocity of stress waves. To increase the amplitude and the duration of the pressure load generated by the laser–matter interaction, the front surface of the target was covered with a confining layer (water and BK7 glass). Preliminary calibration tests involving time-resolved velocity measurements were performed to calculate the ablation pressure on the front surface of foam samples. The calculated pressure loads were used as input data for hydrodynamic simulations, in which the foam is modeled using a homogeneous porous macroscopic model, and model predictions were compared with experimental results. A fair consistency was found for most experiments, while for the others, an overestimation of the applied pressure is suspected, likely due to a laser breakdown within the confining medium. Finally, post-shot x-ray tomography of the recovered samples showed permanent deformation of the foam, unlike what was observed under quasi-static compression, and revealed heavy damage in the vicinity of the loaded zone. [ABSTRACT FROM AUTHOR]

When a shock wave of several tens of GPa breaks out at a free surface, a material is ejected ahead of this surface. The amount and velocity of such ejecta depend on the breakout pressure, state of the released material (solid, liquid, or mixed), whether the shockwave is supported or unsupported, and the initial geometrical perturbation (or roughness) of the free surface. If surface defects consist of small grooves, pits, or scratches, material ejection occurs in the form of jets breaking up into tiny particles (so-called microjetting), with jet tip velocities up to several times higher than the free surface velocity. The laser-based experiments presented in this paper focus on microjetting in shock-melted tin with periodic surface perturbations. Several complementary diagnostics are combined to measure the velocity and mass of ejecta during the early stages of the jetting process. One relevant advancement is the use of ps-laser x-ray radiography to probe the density of the ejecta in distinct jets a few tens of μ m -wide. The effects of the depth and wavelength of the initial perturbation are investigated in both linear and near-linear growth regimes. The results are compared with predictions derived from the Richtmyer–Meshkov Instability theory. [ABSTRACT FROM AUTHOR]

We present a series of shock-wave measurements on aluminum based on the use of a simultaneous Photon Doppler Velocimetry (PDV) and triature velocity interferometer system for any reflector. Our dual setup can accurately measure shock velocities, especially in the low-speed range (<100 m s−1) and fast dynamics (<10 ns) where measurements are critical in terms of resolution and unfolding techniques. Especially, the direct comparison of both techniques at the same measurement point helps the physicist in determining coherent settings for the short time Fourier transform analysis of the PDV, providing increased reliability of the velocity measurement with a global resolution of few m s−1 in velocity and few ns FWHM in time. The advantages of such coupled velocimetry measurements are discussed, as well as new opportunities in dynamic materials science and applications. [ABSTRACT FROM AUTHOR]

Material ejection upon the breakout of a shock wave at a rough surface is a key safety issue for various applications, including pyrotechnics and inertial confinement fusion. For a few years, we have used laser driven compression to investigate microjetting from calibrated grooves in the free surface of shock-loaded specimens. Fast transverse optical shadowgraphy, time-resolved measurements of planar surface and jet tip velocities, and post-shock analysis of some recovered material have provided data over ranges of small spatial and temporal scales, short loading pulses (ns-order), and extremely high strain rates. In the new experiment reported here, picosecond laser irradiation of a thin copper wire generates an ultrashort x-ray burst which is used to radiograph the microjets expanding from plane wedged-shape grooves in tin and copper samples shock-loaded by a longer, nanosecond laser pulse. Such ultrafast radiography provides estimates of the density gradients along the jets and of the total ejected mass at different times after shock breakout. Furthermore, it reveals regions of low density inside the samples deep beneath the grooves, associated with subsurface damage due to tension induced by the interaction of rarefaction waves. Thus, combining this x-ray probe with our former experimental techniques provides a more complete insight into the physics of microjetting at very high loading rates and the ballistic properties of the resulting ejecta. [ABSTRACT FROM AUTHOR]

In a material subjected to high dynamic compression, the breakout of a shock wave at a rough free surface can lead to the ejection of high velocity debris. Anticipating the ballistic properties of such debris is a key safety issue in many applications involving shock loading, including pyrotechnics and inertial confinement fusion experiments. In this paper, we use laser driven shocks to investigate particle ejection from calibrated grooves of micrometric dimensions and approximately sinusoidal profile in tin samples, with various boundary conditions at the groove edges, including single groove and periodic patterns. Fast transverse shadowgraphy provides ejection velocities after shock breakout. They are found to depend not only on the groove depth and wavelength, as predicted theoretically and already observed in the past, but also, unexpectedly, on the edge conditions, with a jet tip velocity significantly lower in the case of a single groove than behind a periodic pattern. [ABSTRACT FROM AUTHOR]

Laser driven shocks allow studying the dynamic behaviour of condensed matter over small spatial (∼μm to mm-order) and temporal (∼ps to ns-order) scales, at extremely high strain rates (∼107 s−1). They can be used to test the predictive capability of constitutive models over wide ranges of loading pressures and pulse durations. We present experimental results in laser shock-loaded metals (iron, gold, tin), based on various, complementary techniques including time-resolved velocity measurements, transverse shadowgraphy and post-shock analyses of recovered samples. The data are used to investigate several shock wave processes such as yielding and polymorphic transformations, melting, spall fracture and dynamic fragmentation in both solid and melted states. On the basis of comparisons with numerical simulations, the abilities and limitations of several models are briefly discussed.

The breakout and reflection of a strong shock-wave upon the free surface of a metallic sample may lead to ejecta production of many types. Spall fracture is due to tensile stresses which result from the interaction of the incident and the reflected release waves. When the sample remains in solid state, one or several layers of finite thickness, called spalls, can be created and ejected. When melting is initiated during shock-wave propagation, tensile stresses are generated in a liquid medium and lead to the creation of an expanding cloud of liquid debris. This phenomenon, sometimes referred to as microspalling, consists in a dynamic fragmentation process in the melted material. The present paper is devoted to the experimental investigation of the transition from spall fracture in solid state to the micro-spalling process in molten metals. This study, realized on tin and on iron, involves different shock generators (gas gun, pulsed laser…) and diagnostics (velocimetry, high-speed optical shadowgraphy, fragments recovery).

Although shock-induced fracture and fragmentation of materials at low temperatures are issues of considerable interest for many applications, such as the protection from hypervelocity impacts in outer space or the ongoing development of high energy laser facilities aiming at inertial confinement fusion, little data can be found on the subject yet. In this paper, laser driven shock experiments are performed on gold and aluminum samples at both ambient and cryogenic (down to about 30 K) temperatures. Complementary techniques including transverse optical shadowgraphy, time-resolved velocity measurements, and post-recovery analyses are combined to assess the effects of target temperature upon the processes of microjetting, spallation, and dynamic punching, which are expected to govern fragments generation and ejection. The results indicate that cryogenic temperature tends to reduce the resistance to tensile and shear stresses, promotes brittle fracture, and leads to slightly higher fragments ejection velocities. [ABSTRACT FROM AUTHOR]

Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as inertial confinement fusion, which involves high energy laser irradiation of thin metallic shells. In this context, we present an experimental and numerical study of debris ejection in laser shock-loaded metallic targets (aluminum, gold, and iron) where fragmentation is mainly governed by spall fracture occurring upon tensile loading due to wave interactions inside the sample. Experimental results consist of time-resolved velocity measurements, transverse optical shadowgraphy of ejected debris, and postshock observations of targets and fragments recovered within a transparent gel of low density. They are compared to numerical computations performed with a hydrodynamic code. A correct overall consistency is obtained. [ABSTRACT FROM AUTHOR]

Phase transition in an interacting triad system equivalent to the Heisenberg stacked triangular antiferromagnet (STA) was analyzed assess to determine whether the renormalization group with a 4 - epsilon expansion indicates a new universality class while that with a 2 + epsilon expansion using a nonlinear sigma (NLS) model is of the known O(4) universality class. The observed critical exponent 0.48 plus or minus .05 is different from the original STA in the absence of local rigidity, suggesting that local rigidity alters the nature of transition. The transition is also different from that of O(4), implying that the O(4) universality class is obtained by future transformations that enable the development of the NLS model from the original STA.

Phase transition in antiferromagnetic stacked traingular lattices with vector spins was characterized using Monte Carlo simulations. The simulation confirmed that transition in the lattices was first-order. The close proximity of the controversy point indicated that the exponents determined by the model were influenced by the first-order region and gave it a tricritical character.