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In this work, the time development of plasmas produced by interaction of laser pulses, with a nitrogen gas, was investigated. The interaction took place inside a small portion of dense nitrogen gas injected temporarily into a chamber filled with the gas under low pressure. High-temperature plasmas produced directly by the laser pulse were a source of soft x rays and charged particles, ionizing and exciting the surrounding gas. In this way, low-temperature plasmas were produced. The formation of high-temperature plasmas was studied using soft x-ray spectroscopy and x-ray streak imaging. Low-temperature plasmas formed at various distances from the laser focus were investigated using an optical streak camera. Interpretation of the experimental data was supported by numerical modeling of the laser-produced plasma hydrodynamics. It was concluded that depending on the distance from the focal spot, the formation of the low-temperature plasmas was dominated by ion streams or by soft x-ray radiation.

The paper shows the estimations of maximal penetration depths of shaped charge jets in a steel armour as a function of stand-off distance to the liner base. The data – in-stantaneous coordinates of positions, masses, and velocities of jet elements were received as results of numerical calculations for selected examples of designs of shaped charges. It was shown that the crater’s depth is a function of acceptable maximal extension of jet elements and their minimal velocity. The results were compared with experimental data.

W artykule zaprezentowano zbadane procesy zbiegania się elementów stożkowej wkładki kumulacyjnej do osi symetrii i podziału na części wewnętrzną wchodzącą do strumienia i zewnętrzną pozostającą w zbitku. Element wkładki miał długość komórki numerycznej i był podzielony na 18 warstw prostopadle do tworzącej wkładki. Pokazano występowanie gradientów prędkości wzdłuż części elementów wkładki tworzących strumień – pierwsze wewnętrzne warstwy elementów wkładki uzyskują maksymalne prędkości. W konsekwencji strumień kumulacyjny ma strukturę warstwo-wą, podobnie jak strumień powstający podczas kumulacji wkładek półsferycznych. Jednorodność osiowa strumienia jest funkcją ziarnistości materiału wkładki, w naszym przypadku rozmiarów komórek numerycznych. Wyniki rozwiązań numerycznych zostały porównane z wynikami obliczeń metodą analityczną opartą na modelu PER.

The earlier papers of the team presented the results of theoretical analyses concerning the interaction of CW laser radiation with metal targets. Laser power ranged from 1 to 10 kW and the thickness of targets ranged between 0.1 and 1 cm. It was also assumed that the beam diameter at an Al target was around 1 cm. The present paper describes another variant of similar interaction, with simultaneous blowing of air on the object surface. Like before, the mathematicalphysical model of the phenomenon was based on the equation of conservation of energy (spatially one-dimensional model – (z,t)), taking into account: radiation absorption and transport inside the target, heat conduction, reflection of part of radiation from the target’s surface and heat losses in the processes of melting and evaporation. Coefficients of light absorption and reflection from the target’s surface were described with semi-empirical expressions which took into account their dependence on temperature and density. Calculations were performed for conditions with and without the removal of melted layers and for two variants of laser radiation pulses: (1) 1 kJ of energy with a duration of 2x10-4 s, and (2) 10 kJ of energy with a duration of 1 s. The most interesting result of the calculations is the effect of significant impact of the blowing out of melted layers to the thickness of melting only in the case of shorter pulses with higher peak power.

Numerical model of 12.7 mm type B-32 projectile and high-strength samples of NANOSBA bainitic steel with hardness of 47 HRC were developed, tested and verified with experiment. Computer codes were adapted and modified using the free points method in version with so-called markers. It referred to a new method of maintaining of the calculation stability and proper selection of weighting factors for calculation of velocity gradients and stresses in the contact areas of materials with different properties. The basic criterion of the numerical model correctness was the shape and depth of penetration of the Armox 500T armor plate on which the bainitic steel samples were placed and fired with the 12.7 mm type B-32 projectile with velocity of 850 m/s. A satisfactory agreement was obtained of the theoretical results with firing tests of the samples, i.e. size and shape of craters in the Armox 500T plate.

The paper presents numerical modeling of interaction of strong laser radiation with conventional aluminum sheets, similar to those used in military technology. The theoretical model uses equations of continuum mechanics (equations of hydrodynamics and the equations of mechanics of solid bodies in a cylindrical coordinates r, z), enriched with equations describing the typical effects of high temperature, such as absorption of laser radiation within the Al shield, electronic and radiative thermal conductivity, and energy loss on phase transitions (melting, evaporation, ionization). Semiempirical equations of state were used to describe the properties of material in the conditions of large deformation and the Johnson-Cook’s model. The equations were solved using the method of free points developed by one of the authors. Two kinds od laser pulses were considered: microsecond pulse with duration of 200 μs and a low peak power of 10 kW/cm2 (CW laser), and nanosecond pulse with duration of 10 ns and high peak power of 5 GW/cm2 (pulsed laser). The aim of this study was to determine the shapes and temperatures of Al plates under the influence of these pulses for the comparison of the numerical results with future experiments and to verify the possibility to determine the distribution of the energy density of the laser beam on the basis of the plate deformation.

Spectral investigations in the UV-VIS range of selected Al, Cu, and Fe alloys and composite materials were performed using LIBS technique. The investigated objects were typical rifle cartridges, mortars, rocket launchers and samples of different type steel, Cu and Al alloys, as well as composite materials of special chemical composition. Two Nd:YAG lasers were applied: a short 4 ns, 60 mJ Brio Quantel/BigSky laser (1064 nm) and a long pulse 200/400 (up to 1000) µs (~ 2/4 up to 10 J) laser (1064 nm) constructed at the Institute of Optoelectronics MUT. This spectrochemical analysis was possible for Al, Cu, and Fe alloys objects for both lasers, and in case of composites only if the samples were irradiated by short laser pulse since in the experiment with the long pulse, all composite materials spectra, in general, were very similar to each other – they imitated a grey/black body spectra. For metal alloys in experiments with a short laser pulse only atomic spectra were observed while for long microsecond laser pulses molecular transitions have been registered for Al alloys. Electron temperatures of plasma created on different materials for short and long laser pulses were found on the base of Boltzmann plots. Temperatures are clearly higher for plasmas generated with a short laser pulse which results from much higher laser power density on the sample surface for short pulse and not from fluence which is 20-40 times larger for long pulse.

The study presents preliminary results of theoretical analyses concerning interaction of quasi-cw laser radiation with an aluminium target. The range of laser power the authors were interested in was from 1 to 10 kW, and target thicknesses from 0.1 to 1 cm. It was also assumed that a laser beam diameter on the target (Al) was around 0.5 cm. A mathematicalphysical model of the phenomenon was based on the equation of conservation of energy (spatially one-dimensional model – (z,t)) taking into account: radiation absorption and transport inside the target, heat conduction, reflection of part of radiation from the target’s surface, and heat losses in the processes of melting and evaporation. Coefficients of light absorption and reflection from the target’s surface were described with semi-empirical expressions, which took into account their dependence on the temperature and density. Initially, a case of target static during heating was considered. Subsequently, the problem of enhancement of radiation interaction with the target (decrease of reflection coefficient) by the use of short (< 20 ns), high power pre-impulse was analyzed. The last case needed expansion of a set of equations with the continuity equation and the equation of motion, to take into account evaporation of target’s surface under influence of the pre-impulse. It was shown that thermal effect of the pre-impulse is practically not influencing final depths of target remelting. On the other hand, damage (matting) of the target’s surface by the pre-impulse, causing the decrease of reflection coefficient can have a substantial influence on the remelting depth.

The paper describes work connected to the investigation of the interaction of strong laser radiation with selected metals, constituting typical materials applied in military technology, like aluminum, copper, brass and titanium. A special laser experimental stand was designed and constructed to achieve this objective. The system consisted of two Nd:YAG lasers working in the regime of free generation (quasi-cw) and another Nd:YAG laser, generating short pre-pulses in the Qswitching regime. During the concurrent operation of both quasi-cw systems it was possible to obtain pulse energies amounting to 10 J in a time period (pulses) of 1 ms. The synchronized, serial operation resulted in energy amounting to 5 J over a time period (pulse) of 2 ms. Variations of the target’s surface reflection coefficient, caused by the interaction of short pre-pulses with high power density were determined. The experiments were performed using a standard Nd:YAG laser with amplifiers, generating output pulses whose duration amounted to 10 ns and energy to 1 J, with near Gaussian profile. Laser induced breakdown spectroscopy (LIBS) was used to analyze the emission spectra of targets under the conditions of the interaction of destructive strong and weak as well as long and short excitation laser pulses. A decay of the spectra in the UV range from 200 to around 350 nm was observed when irradiating the target with a long, quasi-cw destructive pulse. Moreover, in the case of an Al target, some AlO molecular spectra appeared, suggesting a chemical reaction of the aluminum atoms with oxygen.

This letter describes modelling and experimental results of low and high pressure shock waves (of the order of 100 and 1000 bar, respectively) induced by pulse laser radiation. Measurements were performed using piezoelectric polymer PVDF sensors. The results of numerical calculations and their comparison with an experiment have been posted. Measured and calculated results have been used in estimation of the temporary course of signals from a fibre VISAR interferometer which measured the movement velocity of steel plate driven by the analysed shock waves. Description is supplemented with results of magnitude measurements of surface plastic deformation and material microstructure of samples. Full Text: PDF References J. Wang, N.R. Sottos, R.L. Weaver, "Tensile and mixed-mode strength of a thin film-substrate interface under laser induced pulse loading", J. Mech. Phys. Solids 52, 999 (2004). CrossRef R. Ecault et al., "A study of composite material damage induced by laser shock waves", Composites A 53, 54 (2013). CrossRef K. Jach et al., Computer modeling of dynamic interactions of bodies using free point method, Wydawnictwo Naukowe PWN, Warszawa, (2000) (in Polish). D.H. Dolan, Foundations of VISAR analysis, SANDIA REPORT, SAND2006-1950 (2006). CrossRef

The interaction of laser radiation with matter leads to the certain kinds of modelling of its surface or volume. These effects have been demonstrated for a lot of materials, even causing the formation of new scientific and industrial domain, which is undoubtedly laser material processing and as well as laser cleaning of artworks. Those applications lie in the so-called “low''' region of laser energy densities, represented for short laser pulses by power densities below 109 W/cm2. Paper presents set of equations describing in one-dimensional (1D) model phenomena accompanying to laser–matter interaction. Target geometry includes two and four layers of different materials, irradiated by ns laser pulses. Effects of radiation absorption and transport, heat conductivity, target transit to plastic state, melting and evaporation are taken into consideration. The part of the paper is devoted to the discussion of numerical results, selected in such a way to illustrate the phenomenon of radiation interaction with materials as well as to show, in whole, possibilities of computer simulation methods.

The two-dimensional axisymmetric hydrocode model of free particles is applied to the calculation of response of a comet nucleus to a meteorite impact. The nucleus is assumed to be spherical with a radius of 1 km. It is composed of a porous granular mixture of water ice and of mineral. Initial temperature is 50 K. Porosity is ψ = 0.6 and the mean density is ϱ = 400 kg m −3 . Impactor radius is equal to 1 m and its mean density is equal to that of the nucleus. Impact velocity is 10 km s −1 . A normal impact is considered. Particular forms for the equations of state (EOS) for the real medium (water ice and rock) as well as for an artificial medium of very low-density (40 kg m −3 ) filling up the voids are used. The cohesion is included in the constitutive model of the constituents. Numerical modelling provides the time dependent fields of pressure, density, temperature, and particle velocity in the vicinity of an impact point. The evolution of the field of temperature correlated with the function for kinetics of amorphous to crystalline phase transition permits discussion of the impact-induced crystallization of presumably initially amorphous ice.

The possibility of water ice in the Martian subsurface regolith continues to present an intriguing enigma. We submit that any exo-martian source of energy, i.e. meteorite, asteroid or cometary impact, must disturb the equilibrium within the regolith surrounding an impact site. We farther propose impactors with the size range of 100 m and larger with velocities of 10 km s−1 are effective in causing significant temperature increases in the regolith and subsequent ice melting. We present our studies of the crater formation within Martian surface layers that presumably are a solid mixture of regolith and water ice. Mass ratio of rocks to ice, as well as the thermal gradient in the crust, are the parameters. We have completed numerical simulations of a cratering event by means of two-dimensional, axialsymmetric hydrocodes involving a free particles' method in order to provide a simulation of an impact cratering. A fraction of subsurface ice melts and the crater partially forms from mud-like material. Comparison of a calculated crater and observed Martian crater is presented. The simplified analytical estimates concerning melting of ground ice in the regolith surrounding a Martian impact crater are presented.

This paper presents results of numerical calculations of graphite (model medium for black encrustation) removal from aluminium (model medium for artwork substrate) using laser ablation method. Theoretical comparison of cleaning rate of graphite as a solid encrustation as well as porous graphite filled with air or water, using pulsed laser radiation, are presented. Moreover, results of numerical modeling of pressure pulse, generated by laser pulse in graphite filled with water, are shown.

The paper presents influence of laser radiation parameters on velocity of encrustation removal from artworks and heritage architectural objects. The influence of laser fluence and pulsewidth on the velocity of graphite removal from aluminium substrate is discussed on the basis of developed numerical model. Selected experimental results of influence of laser wavelength and fluence on velocity of encrustation removal for different heritage objects are given as well as remarks on laser cleaning process are presented.

Laser pulse duration and its temporal shape are essentials parameters characterizing laser as a heat source used for artworks cleaning. In order to decrease damaging effects of laser cleaning of artworks it is suggested to use laser generation in multipulse Q-switch mode, in which laser emits a sequence of pulses. Then during single pump pulse the transmission of laser generator rises and drops many times, thus generating from several to a dozen or so Q-switched laser pulses, so called burst mode

The paper presents application of laser radiation for cleaning of monuments and art works, using Q -switched Nd:YAG laser generating high power series of pulses in so called "burst mode". The time width of pulse train is 200 ÷ 300 μs. The oscilloscope traces of pulse repetition frequency and the results of energy measurements are shown. Numerical model of interaction of high power laser pulse with graphite layer of aluminium substrate on the base of equations in one-dimensional hydrodynamic approximation is presented. The results of calculations of graphite removal process for single pulse and train of laser pulses are in qualitative agreement with the results of measurements.

Laser emission analysis is an efficient method used for determination of quantitative and qualitative composition of chemical elements in materials. For the analyser designs a proper choice of a laser type, stabilisation of its pulse parameters and performance of a high-resolution spectrometer of sufficient responsivity are crucial problems. The correlation-based method of laser induced breakdown spectrometry for soil contamination was presented. A system of laser induced breakdown spectroanalyser and the investigation of a portable laser emission spectro-analyser for analysis of chemical composition of soil samples are described. The results and examples of its applications are given.

The paper presents results of application of the free particles method for computer modelling of a phenomenon of laser interaction with matter. Alterations made to the method relies on a procedure for modelling of laser radiation absorption and determination of boundary conditions. Computation results for some initial-boundary conditions are presented.

The results of experimental studies on shock wave propagation in plexiglass are discussed. The wave was generated by a single laser pulse of 3 ns and 30 ns duration and of energy from 2 to 30 J. The characteristics of velocity variations of shock wave front propagation are presented in this paper.

Laser radiation is often used in cleaning and conservation of artworks. Interaction of laser radiation with matter is so sophisticated process that analytical solutions rarely bring the valuable formulas. Even numerical methods seldom give quantitative insight into the physics of processes. Chemical and physical properties of surface impurity layers may change from point to point within the same sample. Absorption coefficient of the layers depends on such factors as weather or air humidity. In spite of this, theoretical description of laser cleaning is necessary, as it allows to explain some characteristic features of processes under investigation. In this work we present a model for laser pulse interaction with graphite layer placed on aluminium substrate. The model is limited to one dimensional hydrodynamic equations. The following phenomena are included into the model: absorption and reflection of laser radiation, heat conductivity, radiation transport in grey body approximation, shock waves, ionisation and the elastic properties of the media. Numerical calculations and experimental results give a qualitative agreement.

The term “laser microexplosion” has been introduced to stress the violent character of the optical breakdown by laser radiation under conditions of tight focusing. Generally, the starting phase of the breakdown has been neglected by the assumption of absorption triggered by the presence of damage precursors. The application of the plasticity–elasticity theory in the analysis of the dynamics of this phenomenon has not been extensively examined to date. This paper formulates a phenomenological model attempting to explain the creation of nanovoids in a soft matter under irradiation by a flux of extreme ultraviolet (XUV)/soft x-ray photons. The combined action of plastic deformation and dissociation waves on soft matter is found to be responsible for the material modifications. It is suggested that localized ( volume ≃ λ 3) abundance of energy, coming most likely from photon bunching, constitutes the real onset of the photo-ablative decomposition. It is shown that the coincidental presence of some small number of energy carriers (2–3 XUV photons in the considered case) in such a small volume triggers processes denoted from now on as a laser nanoexplosion. The effect is considered to be the first step in the optical breakdown followed by an intense material removal resembling, to some extent, a phase explosion.