dr hab. Jacek Hoffman

Zakład Wytrzymałości Materiałów (ZWM)
Pracownia Technologicznych Zastosowań Laserów (PTZL)
stanowisko: główny specjalista
telefon: (+48) 22 826 12 81 wew.: 236/235
pokój: 030/034
e-mail: jhoffman

Doktorat
2001Oddziaływanie wiązki lasera CO2 z kanałem parowym w procesie spawania metali 
promotor -- prof. dr hab. Zygmunt Szymański, IPPT PAN
557 
Habilitacja
2016-10-27Badania eksperymentalne ablacji grafitu wywołanej nanosekundowym impulsem lasera 
Ostatnie publikacje
1.Hoffman J., Chrzanowska J., Mościcki T., Radziejewska J., Stobinski L., Szymański Z., Plasma generated during underwater pulsed laser processing, APPLIED SURFACE SCIENCE, ISSN: 0169-4332, DOI: 10.1016/j.apsusc.2017.01.185, pp.1-6, 2017
Hoffman J., Chrzanowska J., Mościcki T., Radziejewska J., Stobinski L., Szymański Z., Plasma generated during underwater pulsed laser processing, APPLIED SURFACE SCIENCE, ISSN: 0169-4332, DOI: 10.1016/j.apsusc.2017.01.185, pp.1-6, 2017

Abstract:
The plasma induced during underwater pulsed laser ablation of graphite is studied both experimentally and theoretically. The results of the experiment show that the maximum plasma temperature of 25000 K is reached 20 ns from the beginning of the laser pulse and decreases to 6500 K after 1000 ns. The observed OH absorption band shows that the plasma plume is surrounded by the thin layer of dissociated water vapour at a temperature around 5500 K. The hydrodynamic model applied shows similar maximum plasma temperature at delay times between 14 ns and 30 ns. The calculations show also that already at 14th ns, the plasma electron density reaches 0.97·1027 m−3, which is the critical density for 1064 nm radiation. At the same time the plasma pressure is 2 GPa, which is consisted with earlier measurements of the peak pressure exerted on a target in similar conditions.

Keywords:
Underwater laser processing, Pulsed laser ablation in liquid, Laser induced plasma, Numerical modelling

35p.
2.Chrzanowska J., Kurpaska Ł., Giżyński M., Hoffman J., Szymański Z., Mościcki T., Fabrication and characterization of superhard tungsten boride layers deposited by radio frequency magnetron sputtering, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2016.04.166, Vol.42, No.10, pp.12221-12230, 2016
Chrzanowska J., Kurpaska Ł., Giżyński M., Hoffman J., Szymański Z., Mościcki T., Fabrication and characterization of superhard tungsten boride layers deposited by radio frequency magnetron sputtering, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2016.04.166, Vol.42, No.10, pp.12221-12230, 2016

Abstract:
The most promising areas of research of new super-hard materials are transition metal borides. These materials are one of the candidates for future superhard layers that will be competitive to DLC and c-BN layers. In this paper MoB-type tungsten boride (WB) layers were examined. WB layers have been deposited by radio frequency magnetron sputtering on Silicon (100), 304 stainless steel (SS 304) and Inconel 601 substrates. Measured thickness of herein prepared layers was about 1 µm, and all studied samples were dense, uniform and smooth. Surface investigation was performed by using an optical profilometer, atomic force microscopy, and scanning electron microscopy. The structure analysis was examined by using X-ray diffractometer (XRD) and transmission electron microscopy (TEM) techniques. Results from the XRD and TEM analysis showed that WB layers were dominated by (101) reflection and indicated a fine grain structure with a grain size of 20–40 nm. The effect of target sputtering power and ambient gas pressure was investigated. The hardness of WB layers deposited on silicon substrate was compared under the load from 1 mN to 5 mN. The hardness of WB layers deposited on SS 304 and Inconel was measured up to 50 mN. All layers of WB revealed excellent hardness exceeding 40 GPa.

Keywords:
Borides, Nanohardness, RF magnetron sputtering, Superhard layers, Tungsten boride

40p.
3.Kamińska A., Hoffman J., Vacher D., Dudeck M., Szymański Z., Electrical and plasma flow characteristics of a segmented plasmatron operating with mixture of gases, PLASMA SOURCES SCIENCE AND TECHNOLOGY, ISSN: 0963-0252, DOI: 10.1088/0963-0252/24/5/055007, Vol.24, pp.055007-1-13, 2015
Kamińska A., Hoffman J., Vacher D., Dudeck M., Szymański Z., Electrical and plasma flow characteristics of a segmented plasmatron operating with mixture of gases, PLASMA SOURCES SCIENCE AND TECHNOLOGY, ISSN: 0963-0252, DOI: 10.1088/0963-0252/24/5/055007, Vol.24, pp.055007-1-13, 2015

Abstract:
The electric characteristics of a segmented plasmatron and the results of optical emission spectroscopy of Ar-air, N2, and N2–CO2 are presented. The main working gas forming the plasma stream was fed near the cathode into the arc region and another additional gas was injected into the plasma stream beyond the arc. It is shown that the gas injected into the plasma stream is drawn to the arc area due to arc spot movement and cyclic arc shrinking and expanding due to the power supply pulsation. It was found that when the anode spot moves upstream, the additional gas is retracted into the arc region, changing the operating conditions of the plasmatron. The retraction mechanism depends on the gas type and is different in argon and molecular plasmas. The results of the plasma emission spectroscopy show differences in the electron excitation and rotational temperatures for the plasmas studied and are used to explain the mechanism of functioning of a segmented plasmatron.

Keywords:
segmented plasmatron, electric properties, optical emission

45p.
4.Mościcki T., Radziejewska J., Hoffman J., Chrzanowska J., Levintant-Zayonts N., Garbiec D., Szymański Z., WB2 to WB3 phase change during reactive spark plasma sintering and pulsed laser ablation/deposition processes, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2015.03.042, Vol.41, pp.8273-8281, 2015
Mościcki T., Radziejewska J., Hoffman J., Chrzanowska J., Levintant-Zayonts N., Garbiec D., Szymański Z., WB2 to WB3 phase change during reactive spark plasma sintering and pulsed laser ablation/deposition processes, CERAMICS INTERNATIONAL, ISSN: 0272-8842, DOI: 10.1016/j.ceramint.2015.03.042, Vol.41, pp.8273-8281, 2015

Abstract:
Reactive spark plasma sintering (SPS) of WB2/WB3 ceramics from elements is studied; the sintering pressure dependence of the ratio of WB3 to WB2 in samples produced by SPS is discussed. Regardless of the sintering pressure, the obtained samples are very hard ~20 GPa. WB3 superhard films prepared by pulsed laser deposition (PLD) from selected SPS targets are presented.

WB3 coatings were prepared on Si (100) substrates using a nanosecond, Nd:YAG laser operating at a 355 nm wavelength. The phase analysis, crystallography, and orientations have been studied using X-ray diffraction (XRD). A WB2 to WB3 phase transformation from 8.2% WB3 in a sintered target to 93.3% WB3 in a deposited film was observed. Additionally, the surface of a SPS sintered WBx target after the ablation process was examined. XRD studies show that already during the laser ablation there is a significant WB2 to WB3 phase transformation. Vickers hardness of sintered samples was measured in macro- and micro-scale, and PLD films in the nanoscale.

Keywords:
Films, Tungsten borides, SPS – sintering, Pulsed laser ablation/deposition

40p.
5.Hoffman J., The effect of recoil pressure in the ablation of polycrystalline graphite by a nanosecond laser pulse, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/0022-3727/48/23/235201, Vol.48, No.23, pp.235201-1-8, 2015
Hoffman J., The effect of recoil pressure in the ablation of polycrystalline graphite by a nanosecond laser pulse, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/0022-3727/48/23/235201, Vol.48, No.23, pp.235201-1-8, 2015

Abstract:
Our experiments with the ablation of graphite by a nanosecond laser pulse showed the formation of craters with a depth of upto 60 µm. The creation of such deep craters is hard to explain solely by evaporation. Existing models should be supplemented by an additional mass removal process that ensures penetration of the material. The recoil pressure at the surface of the target generates a compression wave propagating deep into the material. Possible mechanisms of fracture by the longitudinal compression wave are discussed. A phenomenological model of material fragmentation is proposed. Modelling results are in good agreement with the experiment. The model may be used for polycrystalline graphite as well as other brittle materials treated by the nanosecond laser pulse.

Keywords:
laser ablation, recoil pressure, rigid unloading, graphite

35p.
6.Chrzanowska J., Hoffman J., Denis P., Giżyński M., Mościcki T., The effect of process parameters on rhenium diboride films deposited by PLD, SURFACE AND COATINGS TECHNOLOGY, ISSN: 0257-8972, DOI: 10.1016/j.surfcoat.2015.07.024, Vol.277, pp.15-22, 2015
Chrzanowska J., Hoffman J., Denis P., Giżyński M., Mościcki T., The effect of process parameters on rhenium diboride films deposited by PLD, SURFACE AND COATINGS TECHNOLOGY, ISSN: 0257-8972, DOI: 10.1016/j.surfcoat.2015.07.024, Vol.277, pp.15-22, 2015

Abstract:
Rhenium diboride (ReB2) thin films have been deposited by a nanosecond pulsed laser deposition method on Si (100) substrate heated to 570°C. The coatings were formed in the ablation process of SPS sintered ReB2 target. The effect of laser wavelength, energy density and postannealing on the films' properties was studied. Investigated wavelengths were 355 and 1064 nm of Nd:YAG nanosecond laser. Laser beam energy density varied from 2.1 to 6.1 J cm− 2 and from 4.1 to 9.4 J cm− 2 at 355 and 1064 nm, respectively. Layer thickness was of the order of several hundred nanometres. Deposition efficiency increases with an energy density in quasi linear way and strongly grows for shorter wavelength. The layers consist of two characteristic microstructures: a smooth basis and stick debris (typical diameters of several hundred nanometres). Lower energy density of laser beam and longer wavelength favour dominance of smooth basis and minimization of debris. The XRD analysis of all samples indicate the crystalline ReB2 with preferred (002) orientation and fine grain size of about 20 nm. Shorter wavelength and higher energy density foster stronger (002) orientation. Moreover, an annealing right after the deposition (25 min in 350°C) causes minimization of degree of orientation and decrease of hardness. The Vickers hardness of ReB2 films is at about 60 GPa and is reduced to about 40 GPa after the annealing process. Deposition efficiency and physical and chemical structures of layers produced under variety of conditions were studied and compared.

Keywords:
Ceramics ablation, Pulsed laser deposition, Rhenium diboride, ReB2 optical properties, Super-hard films, Wavelength influence

35p.
7.Mościcki T., Hoffman J., Chrzanowska J., The absorption and radiation of a tungsten plasma plume during nanosecond laser ablation, PHYSICS OF PLASMAS, ISSN: 1070-664X, DOI: 10.1063/1.4933214, Vol.22, pp.103303-1-7, 2015
Mościcki T., Hoffman J., Chrzanowska J., The absorption and radiation of a tungsten plasma plume during nanosecond laser ablation, PHYSICS OF PLASMAS, ISSN: 1070-664X, DOI: 10.1063/1.4933214, Vol.22, pp.103303-1-7, 2015

Abstract:
In this paper, the effect of absorption of the laser beam and subsequent radiation on the dynamics of a tungsten plasma plume during pulsed laser ablation is analyzed. Different laser wavelengths are taken into consideration. The absorption and emission coefficients of tungsten plasma in a pressure range of 0.1–100 MPa and temperature up to 70 000 K are presented. The shielding effects due to the absorption and radiation of plasma may have an impact on the course of ablation. The numerical model that describes the tungsten target heating and the formation of the plasma and its expansion were made for 355 nm and 1064 nm wavelengths of a Nd:YAG laser. The laser beam with a Gaussian profile was focused to a spot size of 0.055 mm2 with a power density of 1 × 109 W/cm2 (10 ns full width half maximum pulse duration). The plasma expands into air at ambient pressure of 1 mPa. The use of the shorter wavelength causes faster heating of the target, thus the higher ablation rate. The consequences of a higher ablation rate are slower expansion and smaller dimensions of the plasma plume. The higher plasma temperature in the case of 1064 nm is due to the lower density and lower plasma radiation. In the initial phase of propagation of the plasma plume, when both the temperature and pressure are very high, the dominant radiation is emission due to photo-recombination. However, for a 1064 nm laser wavelength after 100 ns of plasma expansion, the radiation of the spectral lines is up to 46.5% of the total plasma radiation and should not be neglected.

Keywords:
Plasma temperature, Tungsten, Laser ablation, Laser beams, Plasma pressure

30p.
8.Chrzanowska J., Hoffman J., Małolepszy A., Mazurkiewicz M., Kowalewski T.A., Szymański Z., Stobiński L., Synthesis of carbon nanotubes by the laser ablation method: Effect of laser wavelength, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, ISSN: 0370-1972, DOI: 10.1002/pssb.201451614, Vol.252, No.8, pp.1860-1867, 2015
Chrzanowska J., Hoffman J., Małolepszy A., Mazurkiewicz M., Kowalewski T.A., Szymański Z., Stobiński L., Synthesis of carbon nanotubes by the laser ablation method: Effect of laser wavelength, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, ISSN: 0370-1972, DOI: 10.1002/pssb.201451614, Vol.252, No.8, pp.1860-1867, 2015

Abstract:
The effect of laser wavelength on single-wall carbon nanotubes synthesis yield and their properties was studied. A double-pulse Nd:YAG laser, working at a wavelength of 355 or 1064 nm, was used for carbon nanotubes production. The synthesized carbon nanotubes (CNTs) were investigated using the SEM/STEM microscopy and Raman spectroscopy. The results show that the useful range of UV laser radiation fluence is narrower and the properties of synthesized CNTs depend much more on the laser fluence than in the case of infrared laser radiation.

Keywords:
carbon nanotubes, laser radiation fluence, pulsed laser vaporization, Raman spectra

20p.
9.Nalepka K., Hoffman J., Kret S., Nalepka P., Szymański Z., Laser-deposited Cu/α–Al2O3 nanocomposite: experiment and modeling, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1007/s00339-014-8317-3, Vol.117, pp.169-173, 2014
Nalepka K., Hoffman J., Kret S., Nalepka P., Szymański Z., Laser-deposited Cu/α–Al2O3 nanocomposite: experiment and modeling, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1007/s00339-014-8317-3, Vol.117, pp.169-173, 2014

Abstract:
A Nd:YAG laser operating at a wavelength of 266 or 355 nm is used to deposit a thin layer of copper on the (0 0 0 1)α-Al2O3 surface. The formation process is precisely controlled by identification of time distribution of two characteristics: energy and flux density of particles incident on the substrate. For this purpose, the Cu-plasma expansion is described by means of an analytical hydrodynamic model whose self-similar solutions are fitted to the experimental plasma images and time-of-flight spectra. The obtained nanocomposite is examined by the aberration-corrected high-resolution transmission electron microscopy (Cs-HRTEM) method. The results reveal that copper crystals assume one main orientation relative to the substrate (1 1 1)[2 −1 −1]Cu∥ (0 0 0 1)[−1 −1 2 0]α–Al2O3 and the formed interface has a specific microstructure. To reconstruct the phase boundary region, molecular dynamic (MD) and static (MS) simulations are carried out. The results show that strong bonding between copper and sapphire induces structural changes in the (1 1 1) Cu layer nearest the substrate and leads to formation of the system of partially dissociated dislocations in the next layer. In consequence, the Cu/α–Al2O3 interface becomes the semicoherent system. The lattice matching regions of the individual Cu layers are significantly lowered, which results in strong deformations along the closed packed planes. The reconstructed interface is used for Cs-HRTEM image simulation. A good accordance with the experimental results indicates that the MD model correctly maps the microstructure at the phase boundary of the synthesized nanocomposite.

30p.
10.Hoffman J., Chrzanowska J., Kucharski S., Mościcki T., Mihailescu I.N., Ristoscu C., Szymański Z., The effect of laser wavelength on the ablation rate of carbon, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1007/s00339-014-8506-0, Vol.117, pp.395-400, 2014
Hoffman J., Chrzanowska J., Kucharski S., Mościcki T., Mihailescu I.N., Ristoscu C., Szymański Z., The effect of laser wavelength on the ablation rate of carbon, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1007/s00339-014-8506-0, Vol.117, pp.395-400, 2014

Abstract:
The ablation of graphite is studied as a function of laser fluence for 355, 532 and 1,064 nm wavelength generated by a nanosecond Nd:YAG laser. It has been found that in the case of lower wavelengths, the transition from the thermal ablation to the phase explosion takes place at lower laser fluences. The change of crater shape due to the effect of deep drilling in the proximity of the phase explosion threshold was observed. The calculations of plasma radiation flux to the target surface were made, and the considerable increase of absorbed energy density was found in the case of 355 nm wavelength.

Keywords:
laser ablation, ablation rate, carbon

30p.
11.Kamińska A., Dudeck M., Hoffman J., Szymański Z., Gouy P.A., Vacher D., A plasma jet produced in a segmented plasmatron: modelling and experiment, PHYSICA SCRIPTA, ISSN: 0031-8949, DOI: 10.1088/0031-8949/2014/T161/014072, Vol.T161, pp.014072-1-4, 2014
Kamińska A., Dudeck M., Hoffman J., Szymański Z., Gouy P.A., Vacher D., A plasma jet produced in a segmented plasmatron: modelling and experiment, PHYSICA SCRIPTA, ISSN: 0031-8949, DOI: 10.1088/0031-8949/2014/T161/014072, Vol.T161, pp.014072-1-4, 2014

Abstract:
Nitrogen and argon plasmas with a small admixture of air produced in a segmented plasmatron are studied both experimentally and theoretically. A two-temperature hydrodynamic model is used to simulate the plasma flow inside the plasmatron. The calculated plasma temperature and electron density are in reasonable agreement with the experimental values obtained from emission spectroscopy. The electron temperatures are several thousand kelvins higher than the atom temperatures, showing that the plasmas produced in the segmented plasmatron are in non-equilibrium.

Keywords:
segmented plasmatron, plasma expansion, emission spectroscopy

25p.
12.Radziejewska J., Marczak J., Hoffman J., Sarzyński A., Strzelec M., Zastosowanie laserowo indukowanych fal uderzeniowych do badania dynamicznych właściwości materiałów, INŻYNIERIA MATERIAŁOWA, ISSN: 0208-6247, Vol.XXXV, No.6, pp.544-547, 20147p.
13.Babou Y., Lequang D., Chazot O., Surzhikov S.T., Dikaljuk A.S., Panarese A., Cicala G., Longo S., Hoffman J., Szymański Z., Kamińska A., Dudeck M., Vacher D., Thermodynamic Characterization of High-Speed and High-Enthalpy Plasma Flows, The Open Plasma Physics Journal, ISSN: 1876-5343, DOI: 10.2174/1876534301407010155, Vol.7, pp.155-172, 2014
Babou Y., Lequang D., Chazot O., Surzhikov S.T., Dikaljuk A.S., Panarese A., Cicala G., Longo S., Hoffman J., Szymański Z., Kamińska A., Dudeck M., Vacher D., Thermodynamic Characterization of High-Speed and High-Enthalpy Plasma Flows, The Open Plasma Physics Journal, ISSN: 1876-5343, DOI: 10.2174/1876534301407010155, Vol.7, pp.155-172, 2014

Abstract:
This contribution proposes a description of selected experimental activities conducted in aerospace sciences and dedicated to generate experimental data to assess atmospheric entry plasma models. In order to provide comprehensive set of experimental data, high enthalpy shock tube facilities have been developed to generate plasma representative of entry plasma for broad range of trajectory entry conditions. The shock-heated plasma is obtained through adiabatic compression and the resulting post-shock plasma flow exhibits thermodynamic state analogous to actual entry plasma. However, significant insight can be obtained through experiments conducted also with non-equilibrium plasma flows obtained with other methods. The typical methodologies adopted to provide experimental data of interest to enhance entry plasma modeling are sketched for four distinct non-equilibrium plasma kinds produced respectively by four specific ground facilities. The contribution firstly will consider experimental campaigns conducted with a high enthalpy shock tube in order to document in absolute radiance the radiative signature in the UV spectral range of an Earth entry plasma. Then, the investigations of the interaction between a shock wave and an electrical discharge will be described. These investigations were performed to identify the role of the internal degrees of freedom of molecular gases on the propagation of the shock. Also, the contribution covers investigations devoted to the thermodynamic state characterizations by means of spectroscopic diagnostics in the cases of the non-equilibrium plasmas flows generated by plasma wind tunnels. The examination of the Saha-Boltzmann equilibrium is proposed in the case of a subsonic plasma flow. And at last, the characterization methods of air supersonic plasma jet are presented and the 2D distributions of the subsequently measured plasma properties are documented for a straight comparisons with non-equilibrium plasma jet computations.

Keywords:
Abel transform, multi-temperature model optical emission spectroscopy, non-equilibrium plasma, particle in cell - Monte Carlo computation, plasma wind tunnel, Saha balance, shock tube, supersonic plasma

14.Mościcki T., Hoffman J., Szymański Z., The effect of laser wavelength on laser-induced carbon plasma, JOURNAL OF APPLIED PHYSICS, ISSN: 0021-8979, DOI: 10.1063/1.4819892, Vol.114, pp.083306-1-6, 2013
Mościcki T., Hoffman J., Szymański Z., The effect of laser wavelength on laser-induced carbon plasma, JOURNAL OF APPLIED PHYSICS, ISSN: 0021-8979, DOI: 10.1063/1.4819892, Vol.114, pp.083306-1-6, 2013

Abstract:
The effect of laser wavelength on parameters of laser-ablated carbon plume is studied. A theoretical model is applied, which describes the target heating and formation of the plasma and its expansion, and calculations are made for the fundamental and third harmonic of a Nd:YAG laser. The calculated distributions of plasma temperature and electron density in the early phase of expansion show that plasma temperatures are higher in the case of 1064 nm but the electron densities are higher in the case of 355 nm, which is in agreement with experimental findings. It has been shown that while a higher plasma temperature in the case of 1064 nm is the result of stronger plasma absorption, the greater ablation rate in the case of 355 nm results in larger mass density of the ablated plume and hence, in higher electron densities. An additional consequence of a higher ablation rate is slower expansion and smaller dimensions of the plume.

Keywords:
Plasma temperature, Laser ablation, Laser beams, Absorption coefficient, Carbon

35p.
15.Kamińska A., Hoffman J., Szymański Z., Dudeck M., Plasmatron for Simulation of Re-entry Conditions in a Planetary Atmosphere, IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, ISSN: 1070-9878, DOI: 10.1109/TDEI.2013.6633690, Vol.20, No.5, pp.1607-1615, 2013
Kamińska A., Hoffman J., Szymański Z., Dudeck M., Plasmatron for Simulation of Re-entry Conditions in a Planetary Atmosphere, IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, ISSN: 1070-9878, DOI: 10.1109/TDEI.2013.6633690, Vol.20, No.5, pp.1607-1615, 2013

Abstract:
The characteristics of segmented plasmatron are presented. The arc is sustained in argon plasma and in plasma stream, argon, nitrogen and carbon-dioxide are introduced. The numerical simulation of argon electric arc and plasma stream is carried out and the temperatures and densities of electron and heavy particles are presented. Experimental and theoretical investigations determine and explain the influence of natural gas and flow rate injected into plasma stream on working plasmatron conditions. The anode voltage drop analysis shows that in plasmatron working at a current between 40 and 340 A, gas flow rate between 0.4 and 2 g/s and pressure from 5 to 100 kPa, this drop changes from negative to positive, influencing arc voltage value. The gas injection into plasma stream results in anode spot dynamic. Electric breakdowns accompanied by high voltage fluctuations are observed when argon or nitrogen is introduced while carbon dioxide eliminates this type of breakdown reducing the voltage fluctuations and ablation of electrodes.

Keywords:
segmented plasmatron, re-entry in planetary atmosphere, plasma jet

25p.
16.Hoffman J., Mościcki T., Szymański Z., Acceleration and distribution of laser-ablated carbon ions near the target surface, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/0022-3727/45/2/025201, Vol.45, No.2, pp.025201-1-8, 2012
Hoffman J., Mościcki T., Szymański Z., Acceleration and distribution of laser-ablated carbon ions near the target surface, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/0022-3727/45/2/025201, Vol.45, No.2, pp.025201-1-8, 2012

Abstract:
The plasma plume induced during laser ablation of graphite is studied both experimentally and theoretically. The hydrodynamic model applied shows that the high velocities of the plume observed in the experiment result from the large pressure gradient built up during laser–plume interaction. This means that at a low laser intensity of ∼109 W cm−2 the acceleration mechanism is rather gasdynamical than electrostatic. The calculated temporal profiles of plasma temperature and electron density in the early phase of expansion are in reasonable agreement with experimental profiles obtained from emission spectroscopy. The effect of evolution of the plasma temperature on time-of-flight signals is presented. It has been shown that the appearance of ions with higher charge prior to ions with lower charge often ascribed to the effect of the induced electric field can be explained by the evolution of the plume temperature.

Keywords:
carbon, laser ablation, plasma plume acceleration, hydrodynamic model

35p.
17.Mościcki T., Hoffman J., Szymański Z., Laser ablated carbon plume: experiment and modelling, NUKLEONIKA. INTERNATIONAL JOURNAL OF NUCLEAR RESEARCH, ISSN: 0029-5922, Vol.57, No.2, pp.283-286, 2012
Mościcki T., Hoffman J., Szymański Z., Laser ablated carbon plume: experiment and modelling, NUKLEONIKA. INTERNATIONAL JOURNAL OF NUCLEAR RESEARCH, ISSN: 0029-5922, Vol.57, No.2, pp.283-286, 2012

Abstract:
Laser ablation of graphite is studied both theoretically and experimentally. Plasma temperature and electron density in the early phase of expansion into vacuum are measured as a function of distance from the target. The experimental results agree well with the theoretical simulations. The simulation of ablation shows that plasma plume considerably affects the ablation rate

Keywords:
laser ablation, plasma plume

15p.
18.Hoffman J., Mościcki T., Szymański Z., The effect of laser wavelength on heating of ablated carbon plume, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1063/1.4819892, Vol.104, pp.815-819, 2011
Hoffman J., Mościcki T., Szymański Z., The effect of laser wavelength on heating of ablated carbon plume, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1063/1.4819892, Vol.104, pp.815-819, 2011

Abstract:
The effect of laser wavelength on heating of the ablated carbon plume is studied. The plasma absorption coefficients are calculated in order to analyze the results and an experiment is conducted using the first, second, and third harmonic of a Nd:YAG laser. Plasma temperature and electron density in the early phase of expansion in vacuum are studied as a function of distance from the target. The calculations show that the ratio between absorption coefficients for 1064, 532, and 355 nm is approximately 9:2:1. The experimental results do not agree well with the theoretical predictions. Indeed, the plasma temperatures are highest in the case of 1064 nm but no clear differences between 532 nm and 355 nm have been found.

Keywords:
plasma plume absorption, PLD, carbon, laser wavelength dependence

30p.
19.Mościcki T., Hoffman J., Szymański Z., Modelling of plasma formation during nanosecond laser ablation, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.63, pp.99-116, 2011
Mościcki T., Hoffman J., Szymański Z., Modelling of plasma formation during nanosecond laser ablation, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.63, pp.99-116, 2011

Abstract:
The interaction of laser beam with a target and next with the evaporated material is studied theoretically. In the case of a nanosecond laser pulse with 1064 nm wavelength, the ablation is thermal and therefore the interaction of the laser beam with a target is studied with the use of thermal model. The model which describes both the target heating, formation of the plasma and its expansion consists of equations of conservation of mass, momentum and energy and is solved with the use of Fluent software package. The calculations show a sharp increase of the plume temperature and pressure after plasma formation and following it, a considerable increase of the velocity of plasma plume. Maximum plasma pressure of 2 × 108 Pa, temperature of 61 500 K and front velocity of 3.8 × 104 m · s−1 have been found. The results show that the Mie absorption cannot be neglected in the phase of plasma formation. The shape of the plume and plasma front velocity obtained from the model are close to that observed in the experiment carried out in similar conditions.

Keywords:
laser ablation, plasma formation, plasma expansion

20p.
20.Jedyński M., Hoffman J., Mościcki T., Mróz W., Burdyńska S., Diduszko R., Kołodziejczak P., Szymański Z., Deposition of thin hydroxyapatite films by 335 nm Nd:YAG laser ablation, MATERIALS SCIENCE-POLAND, ISSN: 2083-1331, Vol.28, No.3, pp.693-702, 2010
Jedyński M., Hoffman J., Mościcki T., Mróz W., Burdyńska S., Diduszko R., Kołodziejczak P., Szymański Z., Deposition of thin hydroxyapatite films by 335 nm Nd:YAG laser ablation, MATERIALS SCIENCE-POLAND, ISSN: 2083-1331, Vol.28, No.3, pp.693-702, 2010

Abstract:
The characteristics of hydroxyapatite (Ca10(PO4)6(OH)2) thin films deposited by the pulsed laser deposition technique have been describrd. The laser used was a Nd:YAG, operating at the wavelength of 355 nm. All films were deposited at room temperature, either in ambient water vapour or in vacuum, and were annealed, after deposition in air, at 600 °C. Next, they were examined with the use of an X-ray diffractometer, Fourier transform infrared spectrometer, atomic force microscope, micro scratch tester and scanning electron microscope. The analyses showed that crystalline films exhibiting very strong
adhesion to the substrate have been obtained.

Keywords:
pulsed laser deposition, hydroxyapatite, biomaterials

20p.
21.Wołowski J., Gąsior P., Hoffman J., Kubkowska M., Rosiński M., Szymański Z., Study of laser-induced removal of co-deposits from tokamak plasma-facing components using ion diagnostics and optical spectroscopy, RADIATION EFFECTS AND DEFECTS IN SOLIDS, ISSN: 1042-0150, Vol.165, No.6, pp.434-440, 2010
Wołowski J., Gąsior P., Hoffman J., Kubkowska M., Rosiński M., Szymański Z., Study of laser-induced removal of co-deposits from tokamak plasma-facing components using ion diagnostics and optical spectroscopy, RADIATION EFFECTS AND DEFECTS IN SOLIDS, ISSN: 1042-0150, Vol.165, No.6, pp.434-440, 2010

Abstract:
The paper presents studies of the application of ion diagnostics and optical spectroscopy for on-line measurement of the amount and characteristics of co-deposits from the laser-ablated surface of the plasmafacing components (e.g. graphite tiles). For removal of the co-deposit layer a repetitive Nd:YAG laser was used. Determination of the characteristics of ions emitted from the laser-illuminated targets was performed using ion collectors (on the basis of a time-of-flight method) and an optical spectrometer. The main ion stream parameters and spectral lines of deuterium and carbon or tungsten ions were measured depending on laser pulse parameters. The research proved that optical spectroscopy could be a convenient method for on-line observation of the co-deposited layer removal by means of laser ablation. In combination with the investigation of collected co-deposit dust, the performed study made it possible to state that laser-induced breakdown spectroscopy can be useful as a diagnostic method for the ablative co-deposited layer removal and the wall conditioning. The properties of modified surfaces of samples and collected dust (evaporated co-deposit) were determined using different measuring methods.

Keywords:
laser ablation, laser-induced co-deposit removal, ion diagnostics and optical spectroscopy

20p.
22.Hoffman J., Mróz W., Prokopiuk A., Szymański Z., Plasma plume induced during laser ablation of graphite, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1007/s00339-008-4559-2, Vol.92, pp.921-926, 2008
Hoffman J., Mróz W., Prokopiuk A., Szymański Z., Plasma plume induced during laser ablation of graphite, APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING, ISSN: 0947-8396, DOI: 10.1007/s00339-008-4559-2, Vol.92, pp.921-926, 2008

Abstract:
The plasma plume induced during ArF laser ablation of a graphite target is studied. Velocities of the plasma expansion front are determined by the optical time of flight method. Mass center velocities of the emitting atoms and ions are constant and amount to 1.7×104 and 3.8×104 m s−1, respectively. Higher velocities of ions result probably from their acceleration in electrostatic field created by electron emission prior to ion emission. The emission spectroscopy of the plasma plume is used to determine the electron densities and temperatures at various distances from the target. The electron density is determined from the Stark broadening of the Ca II and Ca I lines. It reaches a maximum of ∼9.5×1023 m−3 30 ns from the beginning of the laser pulse at the distance of 1.2 mm from the target and next decreases to ∼1.2×1022 m−3 at the distance of 7.6 mm from the target. The electron temperature is determined from the ratio of intensities of ionic and atomic lines. Close to the target the electron temperature of ∼30 kK is found but it decreases quickly to 11.5 kK 4 mm from the target.

32p.
23.Jedyński M., Hoffman J., Mróz W., Szymański Z., Plasma plume induced during ArF laser ablation of hydroxyapatite, APPLIED SURFACE SCIENCE, ISSN: 0169-4332, Vol.255, pp.2230-2236, 2008
Jedyński M., Hoffman J., Mróz W., Szymański Z., Plasma plume induced during ArF laser ablation of hydroxyapatite, APPLIED SURFACE SCIENCE, ISSN: 0169-4332, Vol.255, pp.2230-2236, 2008

Abstract:
Plasma plume induced by ArF excimer laser ablation of a hydroxyapatite (Ca10(PO4)6(OH)2) target was studied during expansion into a vacuum or water vapour. The ArF laser operated at a wavelength of 193 nm with a pulse energy of 300–350 mJ and a 20 ns pulse duration. The emission spectra of the plasma plume were registered with the use of a spectrograph and an ICCD camera. The expansion of the plasma plume was studied using the time of flight method. The time-dependent radiation of the Ca I and Ca II lines was registered with the use of a monochromator and photomultiplier at various distances from the target. The dynamics of the plasma plume was also imaged by means of fast photography. It was found that during expansion into a vacuum, the plasma front moved with a constant velocity of 1.75x10^4 m/s, while in thecase of ambient water vapour at a pressure of 20 Pa, velocities of 1.75x10^4–1.5x10^3 m/s were found depending on the distance from the target. Electron densities of 1.2x10^24–4.5x10^21 1/m3 were determined from the Stark broadening of the Ca II and Ca I lines at distances of 1–25 mm from the target.
Temperatures of 11,500–4500 K were determined from the relative intensities of carbon lines and continuum radiation at distances of 4–29 mm from the target. The results allowed the estimation of thermal and kinetic energies of ablated particles. During expansion into a vacuum, the kinetic energies of Ca, P and O atoms were 64, 49 and 25 eV, respectively. During expansion into water vapour, kinetic energies dropped to 0.47, 0.36 and 0.19 eV, respectively at a distance of 25 mm from the target and were comparable to the energies of thermal motion.

Keywords:
Laser ablation, Hydroxyapatite, Plasma plume

32p.
24.Mościcki T., Hoffman J., Szymański Z., Net emission coefficients of low temperature thermal iron-helium plasma, OPTICA APPLICATA, ISSN: 0078-5466, Vol.38, pp.365-373, 2008
Mościcki T., Hoffman J., Szymański Z., Net emission coefficients of low temperature thermal iron-helium plasma, OPTICA APPLICATA, ISSN: 0078-5466, Vol.38, pp.365-373, 2008

Abstract:
Net emission coefficients of low temperature thermal iron-helium plasma mixture at atmospheric pressure are presented. The calculations are made assuming the plasma is in the local thermodynamic equilibrium at a pressure of 0.1 MPa. The results are presented for several values of helium mass fraction in the mixture (between 0 and 1), for a temperature range 3000–25000 K and three characteristic plasma dimensions; 0 – corresponding to the optically thin case, and 1 mm and 10 mm. The values of net emission coefficients allow the estimations of total radiation losses in iron-helium plasmas.

Keywords:
net emission coefficients, iron-helium plasma

13p.
25.Mościcki T., Hoffman J., Szymański Z., Modelling of plasma plume induced during laser welding, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, Vol.39, No.4, pp.685-692, 2006
Mościcki T., Hoffman J., Szymański Z., Modelling of plasma plume induced during laser welding, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, Vol.39, No.4, pp.685-692, 2006

Abstract:
A theoretical modelling of the plasma plume induced during welding of iron sheets with CO2 laser is presented. The set of equations consists of the equations of conservation of mass, energy, momentum and the diffusion equation and is solved with the use of the commercially available program Fluent 6.1. The computations are made for a laser power of 1700 W and for two shielding gases—argon and helium. The results show a significant difference between these two cases. When helium is used as the shielding gas, the plasma is much smaller and burns only where the metal vapour is slightly diluted by helium. In the case when argon is the shielding gas, there are actually two plasmas: argon plasma and metal plasma. The flowfield shows that the velocity increases in the hot region but only part of the mass flux enters the plasma core. In the case when argon is used as the shielding gas, the total absorption of the laser radiation amounts to 18–33% of the laser power depending on argon and iron vapour velocities. In the case of helium the total absorption is much lower and amounts to ~5% of the laser power.

Keywords:
laser welding, CFD, numerical model

32p.
26.Gąsior P., Czarnecka A., Parys P., Rosiński M., Wołowski J., Hoffman J., Szymański Z., Phillips V., Rubel M., Effective laser induced removal of co-deposited layers from plasma facing components in tokamak, CZECHOSLOVAK JOURNAL OF PHYSICS, ISSN: 0011-4626, Vol.56, pp.B67-B72, 2006
Gąsior P., Czarnecka A., Parys P., Rosiński M., Wołowski J., Hoffman J., Szymański Z., Phillips V., Rubel M., Effective laser induced removal of co-deposited layers from plasma facing components in tokamak, CZECHOSLOVAK JOURNAL OF PHYSICS, ISSN: 0011-4626, Vol.56, pp.B67-B72, 2006

Abstract:
An experimental set–up and spectroscopy diagnostic method for laser–induced fuel removal and decomposition of co–deposited layers on plasma–facing components from tokamaks are described. For irradiation of a graphite limiter tile from the TEXTOR tokamak Nd:YAG 3.5-ns pulse laser with a repetition rate of 10 Hz and single pulse energy of up to 0,8 J at 1,06 µm has been used. The spectroscopy system allowed recording of spectra in the visible wavelength range including CII and Dα spectral lines . The evolution of CII and Dα spectral lines was observed pulse–by–pulse during the co–deposit removal. The efficient ablation of the 45 µm thick co–deposit occured after approximately 50 laser pulses.

Keywords:
tokamaks, laser ablation, spectroscopy, co–deposit removal

13p.
27.Hoffman J., Mościcki T., Szymański Z., Modelling of time dependent plasma plume induced during laser welding, CZECHOSLOVAK JOURNAL OF PHYSICS, ISSN: 0011-4626, Vol.56, pp.B938-B943, 2006
Hoffman J., Mościcki T., Szymański Z., Modelling of time dependent plasma plume induced during laser welding, CZECHOSLOVAK JOURNAL OF PHYSICS, ISSN: 0011-4626, Vol.56, pp.B938-B943, 2006

Abstract:
Theoretical modelling of the plasma plume induced during welding of iron sheets with CO2 laser are presented. The set of equations consists of equation of conservation of mass,energy, momentum and the diffusion equation and is solved with the use of commercially available program Fluent 6.1. The computations are made for the laser power of 1700 W and shielding gas argon. Two solutions are taken into account stationary and non–stationary. The results show significant difference between these two cases.

Keywords:
laser welding, simulations, plasma

13p.
28.Hoffman J., Szymański Z., Time-dependent spectroscopy of plasma plume under laser welding conditions, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/0022-3727/37/13/010, Vol.37, pp.1792-1799, 2004
Hoffman J., Szymański Z., Time-dependent spectroscopy of plasma plume under laser welding conditions, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/0022-3727/37/13/010, Vol.37, pp.1792-1799, 2004

Abstract:
Momentary emission spectra of iron and argon lines were measured in a plasma plume induced during welding with a continuous wave CO2 laser. Time-dependent spectra were registered using a fast gate, lens coupled microchannel plate image intensifier placed between a spectrograph and a 1254 silicon intensified target detector connected to an optical multichannel analyser. The results, together with the analysis of the colour images from a fast camera, show that in the case when argon is the shielding gas, two plasmas exist: the argon plasma and the iron plasma. It has been found that during strong bursts the plasma plume over the keyhole consists mainly of metal vapour, not being diluted by the shielding gas. No apparent mixing of the metal vapour and the shielding gas has been observed. The space-averaged electron densities determined from the Stark broadening of the 7503.87, 7514.65 Å Ar I lines amounts to (0.75–1.05) × 1023 m−3 depending on the distance from the surface. Assuming that argon is not mixed with the metal vapour and is in local thermodynamic equilibrium these electron densities correspond to the temperatures of 12–13 kK. At the peaks of strong vapour bursts the space-averaged electron densities determined from the Stark broadening of the 5383.37 Å Fe I line are (0.6–1) × 1023 m−3. Numerical simulations showed that the maximum densities in the plasma centre are considerably higher and amount to ~1.8 × 1023 m−3 and ~2.45 × 1023 m−3 in the case of the argon and metal plasma, respectively. Consequently the absorption of the laser beam in the plasma plume amounts to ~5% of the beam power in the case of argon and 10% in the case of metal plasma.

32p.
29.Mościcki T., Hoffman J., Szymański Z., Emission coefficients of low temperature thermal iron plasma, CZECHOSLOVAK JOURNAL OF PHYSICS, ISSN: 0011-4626, Vol.54, pp.C677-C682, 2004
Mościcki T., Hoffman J., Szymański Z., Emission coefficients of low temperature thermal iron plasma, CZECHOSLOVAK JOURNAL OF PHYSICS, ISSN: 0011-4626, Vol.54, pp.C677-C682, 2004

Abstract:
Iron plasma appears during material processing with laser, electric arc etc., and has considerable influence on the processing conditions. In this paper emission coefficients of low temperature thermal iron plasma at atmospheric pressure are presented. Net emission coefficients εN have been calculated for pure iron plasma as well as for Fe–Ar and Fe–He plasma mixtures. To calculate the recombination radiation the knowledge of the Biberman factors ξz fb(Te, λ) is necessary and they have been calculated from the iron photo–ionization cross sections. The calculations allow estimation of energy losses, energy radiated by plasma plume and its comparison with the energy absorbed from laser beam.

Keywords:
absorption coefficient, plasma emission, Biberman factor

13p.
30.Mościcki T., Hoffman J., Szymański Z., Dynamics of the plasma plume induced during laser welding, OPTICA APPLICATA, ISSN: 0078-5466, Vol.33, No.2-3, pp.433-443, 2003
Mościcki T., Hoffman J., Szymański Z., Dynamics of the plasma plume induced during laser welding, OPTICA APPLICATA, ISSN: 0078-5466, Vol.33, No.2-3, pp.433-443, 2003

Abstract:
The dynamics of the plasma plume produced during laserwelding is quite complex. The keyhole wall oscillates and this results in oscillations of the plasma plume over the keyhole mouth. The metal vapour, which appears in irregular bursts, interacts with the shielding gas flowing from the opposite direction. In the present work, temporary electron densities and temperatures are determined in the peaks of plasma bursts during welding with a continuous wave CO2 laser. It has been found that during strong bursts the plasma plume over the keyhole consists of metal vapour only, without being diluted by the shielding gas. The results, together with the analysis of the colour pictures from sreak camera, allow interpretation of the dynamics of the plasma plume. No apparent mixing of metal vapour and the shielding gas has been observed. In typical bursts the electron density determined from the Stark broadening of Ar I lines varies from 0.9x1023 m-3 near the metal surface to 0.5x1023 m-3 at a distance of 1.5 mm from the surface. Assuming that argon is not mixed with the metal vapour and is in local thermal equilibrium these electron densities correspond to temperatures 12.7 kK and 11.5 kK, respectively. In strong bursts the electron density varies, along the same distance, from 1.6x1023 m-3 to 0.6x1023 m-3 , which corresponds to the temperatures of 14.2 kK, respectively.

Keywords:
laser welding, plasma diagnostics

13p.
31.Kalita W., Kołodziejczak P., Hoffman J., Mościcki T., Szymański Z., Spawanie stopu magnezu AM20 laserem CO2, PRZEGLĄD MECHANICZNY, ISSN: 0033-2259, Vol.7-8, pp.48-51, 20039p.
32.Szymański Z., Hoffman J., Kurzyna J., Plasma plume oscillations during welding of thin metal sheets with a CW CO2 laser, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, Vol.34, pp.189-199, 2001
Szymański Z., Hoffman J., Kurzyna J., Plasma plume oscillations during welding of thin metal sheets with a CW CO2 laser, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, Vol.34, pp.189-199, 2001

Abstract:
An analysis is presented of the oscillations of keyhole pressure and plasma radiation emitted during welding with a continuous wave (CW) CO2 laser. Welding was done with a CW CO2 laser, Photon Sources VFA 2500, operating at the power of 1.75 kW. The welded materials were mild and stainless steel sheets, 0.8–2 mm thick. The shielding gas was argon or helium. Oscillations of plasma radiation were registered in monochromatic or broad band radiation with the use of a photomultiplier or photodiode and pressure variations with a microphone in the frequency range of 20–2 × 104 Hz. It has been found that the optical signal from the plasma plume is closely connected with the acoustic signal and that the source of the acoustic signal is the pulsating movement of the plasma plume. Spectral analysis of the measured oscillations shows differences in power spectra depending on the welding conditions. Generally, two intrinsic frequency peaks in the range of 0.5–4 kHz are always present but the amplitude, frequency and width of the peaks depend on the material and welding conditions. The results show that the optical and acoustic signals emitted during the welding process can be useful for process monitoring. The behaviour of the observed oscillations is characteristic for deterministic chaos. Considerable regularization of the process was observed as an effect of modulation of the laser beam. The modulation factor (Pmax−Pmin)/Pmax was equal to 0.2 and the modulation frequency was 2 kHz. In this case, the intense peak corresponding to the modulation frequency was observed in the power spectrum together with smaller peaks corresponding to the harmonic frequencies.

32p.

Prace konferencyjne
1.Kamińska A., Szymański Z., Hoffman J., Vacher D., Menecier S., Dudeck M., Écoulements ionisés dans des plasmatrons pour la simulation des conditions d’entrée en atmosphéres planétaires, Conference on Modelisation : Atomes, Molécules, Plasmas et Systèmes Dynamiques, 2013-05-23/05-24, Bourges (FR), pp.75-86, 2013
Kamińska A., Szymański Z., Hoffman J., Vacher D., Menecier S., Dudeck M., Écoulements ionisés dans des plasmatrons pour la simulation des conditions d’entrée en atmosphéres planétaires, Conference on Modelisation : Atomes, Molécules, Plasmas et Systèmes Dynamiques, 2013-05-23/05-24, Bourges (FR), pp.75-86, 2013

Abstract:
Deux plasmatrons a arc non transferes sont utilises pour simuler les proprietes du gaz ionise entourant une sonde d'exploration planetaire. Le plasmatron de I'IEPE (Poznan) d'une puissance maximale de 25 kW fonctionne a pression atmospherique et a pression reduite (p>1 kPa) avec de l'argon, de l'azote et des melanges CO2-N2. La source a arc non transfere du LAEPT (Clermont-Ferrand) d'une puissance applicable maximale de 100 kW fonctionne a pression atmospherique avec de nombreux melanges gazeux dont les melanges N2-O2 et CO2-N2. Une modelisation fluide du plasmatron de I'IEPE est presentee pour de l'argon en tenant compte d'un desequilibre thermique Te-T. Des mesures de temperature par spectroscopie d'emission ont ete realisees dans les jets de plasma obtenus avec les deux plasmatrons. La temperature d'excitation de l'azote atomique et la temperature de vibration de la molecule CN ont ete determinees (IEPE). Les temperatures d'un plasma d'air et d'un plasma de CO2-N2 ont ete determinees a partir de l'emission du cuivre (LAEPT)


Abstrakty konferencyjne
1.Radziejewska J., Hoffman J., Szymański Z., Plasma generated during underwater laser shock processing, ICPEPA-10, 10th International Conference on Photoexcited Processes and Applications, 2016-08-29/09-02, Brasov (RO), pp.147, 2016
2.Mościcki T., Hoffman J., Szymański Z., Modelling of the nanosecond laser ablation with the use of Ansys-Fluent, LPPM3, XIV INTERNATIONAL SEMINAR “MATHEMATICAL MODELS & MODELING IN LASER-PLASMA PROCESSES & ADVANCED SCIENCE TECHNOLOGIES, 2016-07-04/07-09, Moscow (RU), pp.58, 2016
3.Chrzanowska J., Denis P., Mościcki T., Hoffman J., Garbiec D., Frąś L., Szymański Z., Characterization of tungsten boride layers deposited in pulsed laser ablation process, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), No.P257, pp.1-2, 2016
Chrzanowska J., Denis P., Mościcki T., Hoffman J., Garbiec D., Frąś L., Szymański Z., Characterization of tungsten boride layers deposited in pulsed laser ablation process, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), No.P257, pp.1-2, 2016

Abstract:
Tungsten boride compounds are very promising new hard and super - hard materials. This kind of materials could be used in production of high-speed tools, durable bearings and nonabrasive surfaces. The hardness of tungsten borides strongly depends on boron content as well as material microstructure. For example hardness of W2B is about 12.4 GPa, WB hardness is 18 – 36 GPa, WB2 hardness is 28.5–39.7 GPa and WB3 hardness is 28.6 – 36.9 GPa. Moreover production of tungsten borides in the form of layers or nano -grained structured increase its hardness even above 40 GPa. Although the properties of tungsten boride structures are known from theoretical calculations, the data concerning structures produced experimentally are scare. Therefore, the properties of tungsten boride layers deposited by pulsed laser deposition (PLD) process are investigated in this paper. Layers were deposited using two types of targets: with boron to tungsten ratio of 2.5:1 and 4.5:1 and with the use of two laser wavelengths: 355 and 1064 nm.

Keywords:
pulsed laser deposition, tungsten borides

4.Radziejewska J., Sarzyński A., Strzelec M., Hoffman J., Moćko W., Evaluation of dynamic hardness and adhesion of thin layer using nanosecond laser pulse, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), No.P232, pp.1-2, 2016
5.Chrzanowska J., Mościcki T., Hoffman J., Garbiec D., Radiofrequency assisted pulsed laser deposition of WBN and ReBN thin films, EUROMAT 2015, European Congress and Exhibition on Advanced Materials and Processes, 2015-09-20/09-24, Warszawa (PL), pp.1-2, 2015
Chrzanowska J., Mościcki T., Hoffman J., Garbiec D., Radiofrequency assisted pulsed laser deposition of WBN and ReBN thin films, EUROMAT 2015, European Congress and Exhibition on Advanced Materials and Processes, 2015-09-20/09-24, Warszawa (PL), pp.1-2, 2015

Keywords:
pulsed laser deposition

6.Słowicka A., Walenta Z., Szymański Z., Hoffman J., Mościcki T., Structure and expansion of a plume emitted during laser ablation of multi-component materials, ISSW30, 30th International Symposium on Shock Waves, 2015-07-19/07-24, Tel-Aviv (IL), pp.562-571, 2015
Słowicka A., Walenta Z., Szymański Z., Hoffman J., Mościcki T., Structure and expansion of a plume emitted during laser ablation of multi-component materials, ISSW30, 30th International Symposium on Shock Waves, 2015-07-19/07-24, Tel-Aviv (IL), pp.562-571, 2015

Abstract:
Pulsed laser deposition is a method frequently used for creating thin films of various materials on
solid substrates. High energy laser pulse causes evaporation of the target material, forming a
plume which subsequently
expands and moves with high speed from the target. Thin film of the
evaporated material is deposited on the substrate placed at some distance in front of the target.
The behavior of the plume influences both the stoichiometry and homogeneity of the deposit
ed
layer

the final product of the process. Better understanding of the process of expansion of the
plume, variation of its structure as well as deposition of the material itself is therefore very
important and should give us opportunity for better contro
l of formation of the deposited layer.

Keywords:
laser ablation, plume expansion, DSMC

7.Hoffman J., Chrzanowska J., Mościcki T., Comparison of WB2.5 thin films deposited by pulsed laser deposition and magnetron sputtering, ITFPC'2015, 7th International Conference on Innovations in Thin Film Processing and Characterization, 2015-11-16/11-20, Nancy (FR), pp.94, 2015
Hoffman J., Chrzanowska J., Mościcki T., Comparison of WB2.5 thin films deposited by pulsed laser deposition and magnetron sputtering, ITFPC'2015, 7th International Conference on Innovations in Thin Film Processing and Characterization, 2015-11-16/11-20, Nancy (FR), pp.94, 2015

Keywords:
pulsed laser deposition, RF magnsteron sputtering, tungsten borides

8.Chrzanowska J., Hoffman J., Denis P., Mościcki T., The effect of substrate heating on the ReB2 layers deposited by PLD method, ITFPC'2015, 7th International Conference on Innovations in Thin Film Processing and Characterization, 2015-11-16/11-20, Nancy (FR), pp.93, 2015
Chrzanowska J., Hoffman J., Denis P., Mościcki T., The effect of substrate heating on the ReB2 layers deposited by PLD method, ITFPC'2015, 7th International Conference on Innovations in Thin Film Processing and Characterization, 2015-11-16/11-20, Nancy (FR), pp.93, 2015

Keywords:
pulsed laser deposition, rhenium borides

9.Mościcki T., Garbiec D., Chrzanowska J., Hoffman J., Pulsed laser deposition of superhard rhenium and tungsten borides, ITFPC'2015, 7th International Conference on Innovations in Thin Film Processing and Characterization, 2015-11-16/11-20, Nancy (FR), pp.99, 2015
Mościcki T., Garbiec D., Chrzanowska J., Hoffman J., Pulsed laser deposition of superhard rhenium and tungsten borides, ITFPC'2015, 7th International Conference on Innovations in Thin Film Processing and Characterization, 2015-11-16/11-20, Nancy (FR), pp.99, 2015

Keywords:
pulsed laser deposition, rhenium borides, tungsten borides

10.Chrzanowska J., Hoffman J., Giżyński M., Mościcki T., Investigation of Wavelength Influence on Rhenium Diboride Films Prepared by PLD Method, INDLAS 2014, 4th International Conference , 2014-05-19/05-23, Bran (RO), pp.24-25, 2014
Chrzanowska J., Hoffman J., Giżyński M., Mościcki T., Investigation of Wavelength Influence on Rhenium Diboride Films Prepared by PLD Method, INDLAS 2014, 4th International Conference , 2014-05-19/05-23, Bran (RO), pp.24-25, 2014

Abstract:
In answer to research interest in production of super hard coatings prepared by pulsed laser deposition (PLD) method, Rhenium Diboride was taken under consideration. PLD is characteristic by necessity to define deposition parameters best for particular substance. ReB2 coatings were prepared with the use of 355 nm and 1064 nm wavelengths of Nd:YAG laser and the influence of laser wavelength on those films preparation was investigated. Deposition efficiency increased with shorter wavelength, however layer’s smoothness was better for longer wavelength. The XRD analysis shows crystalline ReB2 character of achieved samples.

Keywords:
pulsed laser deposition, rhenium diboride

11.Mościcki T., Hoffman J., Antoszewski B., Grabas B., Radziejewska J., Theoretical modelling of laser welding of Ni – Pt spark plug for bio-fuel engine, INDLAS 2014, 4th International Conference , 2014-05-19/05-23, Bran (RO), pp.58-59, 2014
Mościcki T., Hoffman J., Antoszewski B., Grabas B., Radziejewska J., Theoretical modelling of laser welding of Ni – Pt spark plug for bio-fuel engine, INDLAS 2014, 4th International Conference , 2014-05-19/05-23, Bran (RO), pp.58-59, 2014

Abstract:
The interaction of laser beam with dissimilar metals during welding process was studied theoretically. A finite element based three-dimensional transient heat transfer and fluid flow model was applied for prediction temperature distribution and material mixing field as well as weld dimensions. The model was used for study and optimization process parameters of welding of Ni – Pt spark plug for bio-fuel engine. The laser pulse duration and energy, and the angle of incidence of the laser beam to thesurface were analyzed. The shape of the melting pool obtained from the theoretical model was close to experimental results.

12.Mościcki T., Hoffman J., Radziejewska J., Chrzanowska J., Levintant-Zayonts N., Garbiec D., Formation of WB4 thin films using nanosecond Nd-YAG laser, KKNM, 4th National Conference on Nano- and Micromechanics, 2014-07-08/07-10, Wrocław (PL), pp.152-154, 2014
Mościcki T., Hoffman J., Radziejewska J., Chrzanowska J., Levintant-Zayonts N., Garbiec D., Formation of WB4 thin films using nanosecond Nd-YAG laser, KKNM, 4th National Conference on Nano- and Micromechanics, 2014-07-08/07-10, Wrocław (PL), pp.152-154, 2014

Abstract:
Inexpensive Tungsten Tetraboride super hard coatings prepared by pulsed laser deposition (PLD) method are investigated. WB4 coatings were prepared on Si (100), by PLD technique using nanosecond, Nd:YAG laser operating at 355 nm wavelenght. Additionally the surface of SPS sintered WBx target before and after ablation process was examined. Phase change of WB2 to WB4 at the surface of target is observed. The phase analysis, crystallography and orientations have been studied using X-ray diffractometry. The surface layer of target after ablation and deposited films are found to be mostly WB4 phase with hardness HV>28 GPa.

Keywords:
laser mikro/nano engineering, thin films, pulsed laser ablation/deposition, tungsten tetraboride WB4

13.Chrzanowska J., Hoffman J., Kowalewski T.A., Małolepszy A., Mazurkiewicz M., Stobiński L., Szymański Z., Synthesis of Carbon Nanotubes by Laser Ablation Method, KKNM, 4th National Conference on Nano- and Micromechanics, 2014-07-08/07-10, Wrocław (PL), pp.117-118, 2014
Chrzanowska J., Hoffman J., Kowalewski T.A., Małolepszy A., Mazurkiewicz M., Stobiński L., Szymański Z., Synthesis of Carbon Nanotubes by Laser Ablation Method, KKNM, 4th National Conference on Nano- and Micromechanics, 2014-07-08/07-10, Wrocław (PL), pp.117-118, 2014

Keywords:
laser ablation, graphite, carbon nanotubes

14.Kamińska A., Dudeck M., Hoffman J., Szymański Z., Vacher D., Segmented plasmatron for simulation of re-entry conditions in a planetary atmosphere, XXXI ICPIG, XXXI International Conference on Phenomena in Ionized Gases, 2013-07-14/07-19, Granada (ES), Vol.1, pp.11-14, 2013
Kamińska A., Dudeck M., Hoffman J., Szymański Z., Vacher D., Segmented plasmatron for simulation of re-entry conditions in a planetary atmosphere, XXXI ICPIG, XXXI International Conference on Phenomena in Ionized Gases, 2013-07-14/07-19, Granada (ES), Vol.1, pp.11-14, 2013

Abstract:
The experimental studies are carried out to adapt the plasmatron functioning to simulate re-entry conditions in a planetary atmosphere. The plasma flow is produced using argon or nitrogen arc and nitrogen or carbon dioxide is introduced into plasma jet. Although the gas introduced into plasma jet is injected behind the arc it influences the arc characteristics and dynamics of flow. This effect is studied in detail. Emission spectra of atomic nitrogen and ionized molecular nitrogen (N2+) are also recorded and analyzed. The atomic emission is studied in the infra-red region and has allowed the determination of an excitation temperature. The electron density is determined from the continuum radiation, and the rotational and vibrational temperatures are determined from the 1stnegative system of N2+

15.Hoffman J., Mościcki T., Mróz W., Szymański Z., Laser-induced carbon plasma; modelling and experiment, AI30, Acoustical Imaging 30, 2009-03-01/03-04, Monterey, California (US), pp.1-2, 2012
16.Hoffman J., Małolepszy A., Mazurkiewicz M., Stobiński L., Szymański Z., Carbon nanotubes synthesis by the Nd: YAG laser ablation process, III National Conference of Nano and Micromechanics, 2012-07-04/07-06, Warszawa (PL), pp.121-122, 2012
17.Maździarz M., Nalepka K, Szymański Z., Hoffman J., Kret S., Kucharski S., Nalepka P., Atomistic Model of Decohesion of Copper-Corundum Interface, SolMech 2012, 38th Solid Mechanics Conference, 2012-08-27/08-31, Warszawa (PL), pp.204-205, 2012