An inherent problem of Pulsed Laser Deposition (PLD) is the undesired particulate formation which is assigned to the deterioration of the solid target surface upon repetitive ablation and instabilities due to fast phase transitions. It could be expected (and has also been claimed by several authors) that ablating liquid targets, i.e. self-reproducing smooth surfaces allows for particulate-free film deposition. In spite of a couple of impressive experiments, it was not yet clarified whether particulate formation was avoided by the use of the liquid target, or only particulate deposition was avoided by choosing appropriate experimental circumstances. In this paper we aimed at answering this question. For this purpose we deposited indium films by ablating solid and liquid indium targets in vacuum (i.e. we deposited the same metal as we ablated). The substrates were held at roomtemperature in order to collect and preserve the droplets formed. Using molten targets, the particulate number density decreased by orders of magnitude as compared to the solid-target case. However, particulate formation could not be totally eliminated, which led us to the conclusion that this technique does not offer an ultimate solution, either. Keywords: thin films, pulsed laser deposition, PLD, particulates

Sintered targets of ZrO₂, Al₂O₃ and BaTiO₂ are ablated by KrF excimer laser radiation (lambda) equals 248 nm, (tau) equals 25 ns. The processing gas atmosphere consists of O₂ at typical pressures of 10^-3-0.5 mbar. The films are deposited on a Pt/Ti/Si multilayer substrate. The investigations concentrate on the influence of the kinetic energy of the ablated particles on the crystal structure and morphology of the forming films. The kinetic energy is described as a function of the processing gas pressure, the target-to-substrate distance and the fluence of the laser radiation on the target. The compaction of the zirconia and alumina thin films is achieved by particles impinging on the growing surface with kinetic energies above 30 eV. To deposit ferroelectric BaTiO₃ thin films at low substrate temperatures the mean kinetic energy of the Ba particles have to be < 30 eV to prevent displacements beneath the film surface. Analytical techniques used for the structural characterization of the films are X-ray diffraction, micro- Raman spectroscopy and electron microscopy. Dielectric and ferroelectric properties of the films are determined by impedance measurements. The thickness and the complex refractive index are determined by fitting a model for the film geometry to the measured ellipsometry data.

Pulsed laser deposition is used in this work to produce zirconia thin films. Targets are sintered zirconia ceramic pellets which are fully or partially stabilized with either 3%mol. Y₂O₃, 20%mol. MgO or 9%mol. CaO. Depending on the stabilizing oxide, their structure is either tetragonal or cubic in the presence of an eventual monoclinic secondary phase. The targets are laser irradiated with a KrF excimer laser (248 nm) at an energy density of 4J/cm² per pulse in an oxygen residual pressure of 0.3 mbar. The ejected matter is collected on fused quartz substrates. These are heated during deposition at temperatures T_s ranging between 400 and 600 degree(s)C. Both targets and films are analyzed via normal incidence and low angle X-ray diffraction and the optical band gap of the films is evaluated via IR-VIS-UV optical transmission. Preparation conditions are then defined which allow to produce films possessing remarkably the same crystalline structure as the corresponding target.

In this work an overview of active planar waveguide systems created by various technologies and especially by method of pulsed laser deposition is given. Parameters of created planar waveguide lasers are summarized. Our experiences with laser deposition and characterization of thin films of Ti:sapphire, Nd:YAG and Nd:YAP are presented. For film deposition a KrF excimer laser was used. Film properties were characterized by XRD, mode spectroscopy, and by study of attenuation and luminescence spectra. Films exhibit waveguiding properties. The waveguide losses as low as 1 dB/cm for Ti:sapphire/sapphire and 0.5 dB/cm for Nd:YAP/(0001)sapphire were measured.

Epilayers of ZnSe and Cd_1-xZn_xTe have been deposited on (100)GaAs substrates by a pulsed laser deposition technique. The ZnSe target was a polycrystalline block of high purity and the different Cd_1-xZn_xTe targets were either polycrystalline or cold-pressed samples obtained by mixing the binary CdTe and ZnTe powders. The surface morphology, the crystalline and optical quality of these epilayers are investigated and compared to MOCVD- grown layers.

The photoluminescence properties of CdSe and CdS films deposited on GaAs substrate by means of laser ablation technique are studied as a function of temperature. The free excitonic recombination is used to determine the energy gap position in the entire temperature range from 10 to 300 K. Semiempirical models well fit the experimental data, so allowing to determine material dependent parameters, related to exciton-phonon and exciton-impurity scattering.

ZnS_xSe_1-x and CdS_xSe_1-x thin films have been successfully deposited in optimized conditions on quartz by ablating stoichiometric cold pressed targets. From X-ray diffraction analysis the interplanar distance d for cubic ZnS_xSe_1-x and the c-axis value for hexagonal CdS_xSe_1-x thin films as a function of Sulfur concentration (x) have been calculated. From room transmittance and reflectance measurements the energy gap modulation, the absorption coefficient and the real part of the refractive index were calculated and compared with those of the corresponding bulk alloys. The analytical dependence of the energy gap and the reticular parameters d and c vs the x-value have been also deduced.

Si_1-yC_y and Si_1-x-yGe_xC_y layers were grown by multiple energy ion implantation of Ge and C into single crystal Si followed by pulsed excimer laser induced epitaxy. The properties of the alloy layers obtained by this technique, in terms of film crystallinity, Ge and C redistribution and substitutional incorporation, strain formation and relaxation, SiC precipitation and C- induced band gap modification are demonstrated to depend strongly on both ion implantation and laser processing conditions. The growing of large area pseudomorphic epitaxial alloys of group IV semiconductor elements, using the high energy beam excimer laser (up to 1 J/cm² per pulse over 40 cm²) developed by SOPRA for industrial applications, is described.

Reactive Pulsed Laser Ablation and Deposition has been applied to the production of InN thin films. Emission spectroscopy and Time of Flight mass spectrometry have been used for the diagnostics of the intermediates formed by reaction of indium atoms and ammonia. The ionization potential (IP) of In(NH₃) cluster has been measured and a strong red shift respect to the IP of bare indium atom has been found. This result indicates that the lone pair of the ammonia strongly interacts with the empty 5p orbitals of In and that the cation In(NH₃)⁺ is more strongly bounded than the corresponding neutral complex. The InN thin films produced through the reaction of In atoms and NH₃ have been characterized by conventional techniques.

Bismuth films were prepared by pulsed laser depcsition (PLD) onto glass or oriented Si(100) substrates. They were characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and X ray diffraction. Influences of the presence of a gaseous background, the deposition temperature, the nature of substrate and the deposition duration on the growth of bismuth films have been studied. All these parameters play an important role in the way of growth. Well crystallized and dense films presenting smooth surfaces are achieved for a deposition temperature of 70°C. Similar textures are obtained on both glass and Si(100) substrates after long deposition durations whereas the beginning of growth takes place in a completely different manner. Keywords: pulsed laser deposition, thin films, bismuth, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X ray diffraction

Lead-based ferroelectric thin films offer a wide variety of applications in dielectric, piezoelectric, pyroelectric, electro-optic, and memory devices. Among many applications, Pb-based thin films are suitable for increasing the integration of DRAM due to high relative dielectric constant. Thin films of PLT(28) Pb_0.72La_0.28Ti_0.93O₃) have been deposited on Pt/Ti/SiO2/Si substrates in situ by a laser ablation. We have systematically investigated the effect of deposition temperatures on the crystal structures and the electrical property of the films. The temperature has been varied from 500 degree(s)C to 700 degree(s)C. The crystal structures and the electrical properties of the thin films have been observed to strongly depend on the deposition temperature by C-V measurement, scanning electron microscopy, and X-ray diffraction method.

This paper presents recent results on the synthesis by pulsed laser deposition (PLD) and optical properties of composite thin films consisting of metallic nanocrystals embedded in an amorphous host. The films are grown by alternate ablation of the metal and host targets in vacuum by means of an ArF laser. The results show that PLD is a very promising technique for producing these materials with nanocrystals of controlled size and in-depth distribution. The analysis of the structure of the films as a function of the number of laser pulses in the metal target allow us to discuss the nanocrystals growth mechanism. A survey of works reporting the synthesis of similar films with metallic nanocrystals embedded in an insulator host and exhibiting third order optical nonlinearities is included, which evidences that the films grown by PLD have excellent properties for waveguide applications.

Pulsed laser deposition with KrF-excimer laser radiation ((lambda) equals 248 nm, (tau) equals 25 ns) is used to grow thin films of diamond-like carbon (DLC) on Si substrates by material removal from a graphite target in vacuum (10^-5 - 10^-4 mbar) or in processing gas atmospheres (He, Ne, Ar, Kr, p approximately equals 10^-2 mbar). Additional ion bombardment is performed by extracting inert gas ions from a low pressure rf gas discharge which is ignited in the deposition chamber. Raman spectroscopy reveals that the sp³-content of the DLC films depends on the fluence of the laser radiation on the target, the substrate temperature and processing gas pressure. Especially the applied laser fluence and the inert gas pressure strongly influence the energy of the film-forming particles and therefore the relative amounts of sp² and sp³ bonds in the films. Using additional ion bombardment from the low pressure gas discharge leads to more nanoclustered films in the case of higher ion masses due to a more effective defect creation. However, the films are predominantly sp²-bonded, caused by substrate heating due to dissipation of electric energy at the substrate electrode.

Carbon nitride films were deposited on <111> Si substrates by pulsed laser ablation of graphite targets in low pressure (1 - 50 Pa) N₂ atmosphere. The irradiations were performed with an XeCl excimer laser at the fluences of 12 and 16 J/cm². Many different diagnostic techniques (SEM, RBS, XPS, XRD, TEM) have been applied to characterize the deposited layers. The deposition rate decreases with increasing ambient pressure. The N/C atomic ratio into the deposited films generally increases with increasing ambient pressure and laser fluence. N/C values up to 0.7 were inferred from the RBS spectra. There are evidences of the formation of quite large crystals, which have grown almost epitaxially on the <111> Si substrate. Heating of the substrates during depositions causes a reduction of the N/C ratio. Optical emission spectra of the laser plasma plume have been recorded and analyzed, to try to correlate plasma characteristics with the composition of the deposited films.

In our laboratories we are interested to new superconducting oxides grown by Pulsed Laser Ablation. The SmBaCuO is a new material which has high critical transition temperature and very good critical current. We begin to study the optical spectroscopic data produced by laser interaction with a target and we characterize the structure and the morphology of thin films obtained using x-ray diffraction spectra and Scanning Electron Microscope analysis.

Crystalline GaN thin films have been deposited by laser ablation of liquid Ga target in nitrogen reactive atmosphere. A Nd-YAG laser (l equals 1.06 mm, t_FWHM equals 10 ns) able to deliver an energy of 0.35 J/pulse was used as laser source. The nitrogen pressure was varied in the range of 10^-2 - 10^-1 mbar. As substrates sapphire plates, heated below 300 degree(s)C, were used. The characteristics of the deposited films were evidenced by different techniques as XPS, SIMS, X-ray diffraction, optical absorption spectroscopy. The Nls region of the XPS spectrum contains as main peak the one centered at 397.3 eV and corresponding to Ga-N bond. From the distance between the photoelectron Ga 3d peak and the Auger Ga LMM peak, the calculated Auger parameter of 1083.9 eV corresponds to the one reported in literature for GaN compound (1084.05 eV). SIMS profiles corresponding to N and Ga in depth- distribution carried out the presence of layers of the order of 130 - 150 nm, with uniform distribution of Ga and N inside the layer. Both techniques evidenced an oxygen contamination below 5%. XRD recorded spectra show the presence of a strong peak assigned to (002) GaN crystalline orientation. Optical absorption spectroscopy studies in the UV and visible range evidenced a high transparency for the deposited films.

C-axis oriented superconducting YBCO thin films on Hastelloy (Ni-Cr-Mo alloys) with yttria-stabilized zirconia (YSZ) buffer layers were fabricated by in situ pulsed laser deposition in a multitarget processing chamber. Generally, it is difficult to make films on flexible metallic substrates due to inherent interdiffusion problems between metallic substrates and superconducting overlayers. To overcome this difficulty, it is necessary to use YSZ buffer layers since it will not only limit the interdiffusion process but also minimize the surface microcrack formation due to smaller mismatch between the film and the substrate. In order to enhance the crystallinity and the transport properties of YBCO films on metallic substrates, YSZ buffer layers were grown at various temperatures different with the deposition temperature to grow YBCO films. On YSZ buffer layer grown at higher temperature than that for YBCO film, the YBCO thin film was found to be textured with c-axis orientation by x-ray diffraction and had a high zero- resistance critical temperature of 85 K. Critical current density for this film at 77 K was 4.7 X J/cm².

The preparation by a multi-target ablation method of films consisting in an attempt to texture CuO₂ planes via the YBa₂Cu₃O₇ structures, is investigated. All films are superconducting with onset temperatures ranging between 68 and 80 K. X-ray data show that the observed phases are both orthorhombic with c parameters close to YBCO-123 and 124. Infrared data indicate additional unknown phases which are not (or poorly) periodic, and likely inter-grown with periodic phases.

We have studied the effects produced by the laser irradiation with 355 nm photons on a heterostructure made of three independent GaAs/Ga_0.67Al_0.33As quantum wells. By comparing the luminescence of the three quantum wells before and after the laser irradiation for different durations and fluence values one could determine if the structure of each quantum well has been altered or not. Then we achieved complementary observations of the irradiated multi-quantum wells structures, using both scanning and transmission electron microscopy. We came to the conclusion that the alteration of the multi-quantum wells structure results from two main consequences of the sample pulsed laser heating: the formation of an altered layer which accompanies the pulsed laser sputtering process and the thermal diffusion process.

Ag₇₅Co₂₅ films were codeposited by two electron beam sources in UHV system on the Si/SiO₂ substrate. The films were thermally processed by rapid thermal annealing (RTA) at 500, 750 and 1000 degree(s)C for 30 s and by XeCl excimer laser irradiation at the fluences F equals 0.1, 0.15 and 0.2 Jcm^-2 and number of pulses n varying from 1 to 100. The samples were analyzed by X-ray diffraction (XRD), grazing incidence XRD, transmission electron microscopy (TEM) and selected area electron diffraction (ED). The electrical resistance R(H,T) was measured up to 50 kOe with magnetic field perpendicular or parallel to the film plane and with current in plane of the sample, from 4.2 K to 300 K. Angular dependence of R(H) was measured as well. The performance of films under laser irradiation was approximated by computer simulations of simplified structures. In the XRD spectra of as-deposited films well developed fcc Ag phase dominates. With RTA a pronounced fcc Ag and fcc Co phase separation and increasing grain size with increasing annealing temperature occur. On the contrary, after laser irradiation more random and less equilibrium structures with smaller grain size developed. This conclusion was confirmed by TEM and ED. The giant magnetoresistance (GMR) of Ag₇₅Co₂₅ films is equals 74% at 4.2 K and 11.3% at 300 K in the as-deposited state. The GMR at 4.2 K can be increased by laser irradiation to 82% at the most severe irradiation conditions (F equals 0.2 Jcm^-2, n equals 10) and to 13.2 - 13.5% at 300 K at the applied fluences. The increase of GMR is ascribed to the formation of a more random structure with smaller grain size. The temperature dependence of magnetic contribution responsible for GMR R_m obeys the power law R_m approximately -Tⁿ with n equals 1.67. This dependence is ascribed to the electron-magnon interaction.

We discuss the study of the kinetic aspects of charge trapping and defect creation which result from the intense electronic excitation caused in wide bandgap dielectrics by an intense laser irradiation. Because of the ultrashort time constants of such processes, they can only be studied using intense subpicosecond laser sources. More precisely, we present the results obtained in a number of optical material using a special interferometric measurement of the instantaneous refractive index, which allows to determine whether the photoinjected carriers are still in the conduction band or trapped in the deep defect states. Different types of materials (oxides and alkali halides) supporting excitonic charge trapping are studied, and a number of effects of the experimental conditions (in particular: excitation density and charge trapping impurity content) are described.

We examine experimentally the modifications induced at the surface of silicon and IV-IV alloys by an excimer laser above the melting threshold fluence. Laser irradiation takes place under vacuum, or in the presence of a gas. The resulting processes are respectively: laser induced polarization, pulsed laser induced epitaxy, incorporation of atoms from the gas phase, and laser chemical etching. In turn, the laser induced surface modifications and the presence of adsorbates on the surface cause important changes in the melting/solidification cycle. We describe a model calculation which takes into account non-equilibrium heat diffusion, phase change, atom diffusion, segregation and desorption. The model is applied to the laser chemical etching process, and its results are compared to the experimental data. This simulation brings information on the segregation of chlorine and on the dynamics of desorption.

Surface modification of YBa₂Cu₃O_7-x (YBCO) target in the process of pulsed laser deposition was systematically investigated by Scanning Electron Microscopy (SEM). We observed that the size of cones formed on YBCO target by pulsed laser became larger with increasing the laser energy density. The image of SEM shows the difference of cone formations at the boundary and at the center of the ablated area on the target surface. This nonuniform modification of the ablated area is supposed to be mainly due to Gaussian profile of the laser beam and the difference of thermal conductivities of the ablated area. To eliminate cones, we have used the method of rotating the target by 180 degree(s) to shot the same number of laser beams on the same spot from opposing angles. Experimental results of losing the directionality and changing the shape of cones formed on YBCO target surface by laser beams incident on the same spot from opposing angles are obtained. These results are mainly due to altering irradiation geometry because cones develop only under unidirectional laser beam. Raman spectroscopy illustrates that the target phase is less degraded by the laser beams incident from opposing angles than the laser beams incident from one direction.

A model for ultraviolet induced chemical vapor deposition (UV CVD) for a-SiN:H is described. In the simulation of UV CVD process, activate charged centers creation, species incorporation, surface diffusion, and desorption are considered as elementary steps for the photonucleation and photodeposition mechanisms. The process is characterized by two surface sticking coefficients. Surface diffusion of species is modeled with a gaussian distribution. A real time Monte Carlo method is used to determine photonucleation and photodeposition rates in nanostructures. Comparison of experimental versus simulation results for a-SiN:H is shown to predict the morphology temporal evolution under operating conditions down to atomistic resolution.

Tin oxide pattern generation by laser deposition from SnCl₄(DOT)5H₂O in isopropanol is reported. Smooth, even stripes of thicknesses ranging from 20 to 120 nm with sharp, well defined edges and cross-section are deposited by scanning an Ar⁺ laser beam ((lambda) equals 514.5 nm) focused onto the substrate--solution interface with a constant speed of 1 mm/s. The linewidth linearly increases from 26 to 42 micrometers with increasing the power from 40 to 120 mW. The reproducibility of pattern generation is extremely good as revealed by scanning electron microscopy, energy dispersive X-ray and micro-area Rutherford backscattering analyses. The minimum DC resistivity of 1.7(DOT)10^-2 (Omega) cm, measured without any process optimization, favorably compares with those reported for films prepared by other techniques. The chemical composition of the film material in SnO_x with 1.1 < x < 1.5 as determined by X-ray photoelectron spectroscopy.

Diamond thin films promise excellent performances in several high value applications such as high temperature and high frequency electronic devices, as electrode material in electrochemistry, and as a protective coating for components operating in aggressive environments. These interesting perspectives, however, are actually limited by the polycrystalline, randomly oriented morphology of CVD deposited films, which results in a noticeable surface roughness with some presence of pin holes. Many methods have been tried to polish diamond, the hardest known material; a very simple and effective one seems to be the irradiation with high energy pulsed lasers. The purpose of this work is to get a deeper insight into the interactions and effects of intense laser radiation on diamond, a wide band gap material, and to explore the optimal experimental conditions to smooth the surface roughness and eventually to fill in the pin-holes. HF-CVD deposited diamond films have been treated by radiations of energy values larger (ArF, (lambda) equals 193 nm, hv is congruent to 6.4 eV) and smaller (Nd:YAG, (lambda) is congruent to 532 nm, hv is congruent to 2.3 eV) than the electronic energy gap (hv is congruent to 5.4 eV). The surface morphology modifications have been studied by SEM. Raman spectroscopy was employed to evaluate some phase transition in the C component (diamond yields DLC yields graphite yields amorphous C).

Recent experimental and theoretical studies have been developed on photodesorption of the submonoatomic sodium coatings from the sapphire surface under the action of the first and the second harmonic radiation of a neodymium laser. It is shown that with increasing the excitation intensity the linear ((lambda) equals 532 nm) or quadratic ((lambda) equals 1064 nm) growth of photodesorption intensity is changed by the threshold exponential growth resulting in the saturation due to complete devastation of the surface. The earlier model of resonance photoatomic desorption has been extended into higher intensities. The speed of the `heating' of adsorbed atoms has been calculated in conditions of multiphoton resonance radiation absorption. The rate of the adsorbate-adsorbent energy exchange has been estimated, indicating close agreement with our earlier measurement of the accommodation coefficient of an atom impacting a surface.

Photopolymers based on the triazeno chromophore group (-NequalsN-N<) have been developed. The absorption properties can be tailored for a specific irradiation wavelength (e.g. 308 cm XeCl laser). The photochemical exothermic decomposition yields high energetic gaseous products which are not contaminating the surface. The polymer can be structured with high resolution. No debris has been found around the etched corners. Maximum ablation rates of about 3 micrometers / pulse were achieved due to the dynamic absorption behavior (bleaching during the pulse). No physical or chemical modifications of the polymer surface could be detected after irradiation at the tailored absorption wavelength, whereas irradiation at different wavelengths resulted in modified (physical and chemical) surfaces. The etching of the polymer starts and ends with the laser pulse, shown by ns-interferometry, confirming that the acting mechanism is mainly photochemical. TOF-MS revealed fragments which are also totally compatible with a photochemical decomposition mechanism.

A novel technique for microstructuring various materials with excimer laser radiation is presented. A thin film of water is deposited on the surface during excimer laser machining. This method leads to some important advantages compared to the conventional dry excimer laser processing. The redeposition of ablated material is completely avoided resulting in a better quality of the microstructures. A subsequent removal of debris is not necessary. Melting of the irradiation material is reduced by applying a thin water film to the surface. Even microstructuring of metals by excimer laser radiation--up to now a problem due to the formation of a strong melting phase--becomes possible. For some ceramic materials (Al₂O₃) the ablation rate is increased significantly. Experiments were carried out with KrF and XeCl excimer lasers. The investigated materials were ceramics (Al₂O₃, Si₃N₄, SiC), glass, metals (stainless steel) and polymers. The ablation rate and quality of the microstructures was examined as a function of the processing parameters. The influence of the water film during the excimer laser ablation on the four-point bending strength of Al₂O₃ and Si₃N₄ was investigated.

Thin layers of polycrystalline antimony and amorphous selenium are successively deposited onto a glass substrate. Under specific CW Ar⁺ laser irradiation conditions in these Sb/Se bilayered films, optical microscopy evidence for a spherulytic crystal growth is obtained. Phase forming is characterized by low angle X-ray diffraction, reflection high energy electron diffraction, energy dispersive X-ray analyses, and Auger spectroscopy. It is shown that, though depending on the laser irradiation conditions, the final spherulytic growth in the irradiated Sb-Se films stems from the Sb-innermost layer crystallization process. Spectacular trans-crystallization takes place through the film during laser treatment of the bilayer. An attempts at modeling this CW-laser induced recrystallization is proposed.

One-step process surface modifications of AlN ceramics have been obtained by UV laser irradiation ((lambda) equals 248 nm). Results concerning some physical and chemical property modifications of AlN surface are here reported. Characterizations by optical microscopy, energy dispersive spectroscopy and grazing X-ray diffraction (XRD) have lead to show the `metallization' process induced by the laser irradiation under particular conditions, due to the AlN decomposition and the Al metal formation. Grazing XRD has clearly shown the Al presence into the laser impacted zones. Electrical resistance measurements have confirmed this surface `metallization' by the highlighting of a very sharp transition zone between the insulator substrate (R > 20 M(Omega) ) and an Al-rich conductive path (R approximately equals 10 - 20 (Omega) ) on only a few 10 micrometers . These last measurements have allowed to easily define efficient laser conditions regarding to this `metallization' process: about 20 laser pulses of 20 ns under a fluence of about 2.0 J/cm² seems to lead to an homogeneous conductive path on insulator AlN substrate.

Ag/Co multilayers (MLs) showing the giant magnetoresistance (GMR) were prepared by electron beam evaporation in UHV apparatus. The samples were thermally processed by XeCl excimer laser at the fluences F equals 0.1, 0.15 and 0.2 Jcm^-2 and number of pulses between 1 and 200. The samples were analyzed by X-ray diffraction (XRD) and grazing incidence (GI)XRD. The electrical resistance R(H,T) was measured up to 50 kOe with magnetic field perpendicular or parallel to the film plane and with current in plane of the multilayers from 4.2 K to 300 K. Four different types of MLs were studied. In one of them (2 nm Ag/l nm Co)x5, Ag layers melt under laser irradiation according to our numerical computations and the change of GMR is non-systematic. In the other MLs (6 nm Ag/l nm Co)x5, the Ag and Co layers don't melt and the GMR improvement vs. deposited laser energy is systematic. This effect is ascribed to the transformation of continuous Co layer into discontinuous one with larger interfacial area between non-magnetic and magnetic components in the ML. The temperature dependence of the magnetic contribution responsible for GMR (R_m) obeys the power law R_m approximately -Tⁿ with n changing from 0.89 to 1.3 for various MLs in as-deposited and irradiated state.

We report the results of designed method of the recrystallization of Bi(2212,2223) and YBCO(123) HTSC ceramics, consisting of laser amorphization and short-time thermal annealing, which was used to enhance the structure and the transport properties of HTCS ceramics prepared by pressing. Cw CO₂ laser ((lambda) equals 10.6 micrometers ) with the average power 100 W was used as a laser source. Short- duration melting of high-T_c superconducting ceramics by CO₂ laser, in combination with a short heat treatment, produced a denser fine-grained structure (grain size 2 - 3 micrometers ). The resultant structure contributed to a considerable increase in the critical current of the superconductors: in 1 - 2 orders of magnitude depending on a type of the material at 77 K and 2 - 3 orders at 20 K. Our results demonstrate the feasibility of laser amorphization of HTSC ceramics in an almost single-phase state with its chemical composition close the composition of the initial unmelted compound and with an almost unchanged area of the fused zone. Heat treatment of this amorphized zone restored the chemical composition to its initial ratio and made it possible to form grains of different types.

First demonstration is given here about the use of a VUV coherent source at 125 nm for efficient and clean etching of polytetrafluoroethylene PTFE and poly(methyl methacrylate) PMMA polymers. Measurements of etch rate as a function of fluence and number of shots are presented and compared with previous works using 157 nm (F₂ laser) and 193 nm (ArF laser). Experimental results are presented and physical approach is made with classical Beer-Lambert's absorption law and discussed.

UV laser induced ablation of YBCO superconducting targets was studied in the initial and late evolution stages in order to control and optimize the thin film deposition process. The optimum irradiation energy was estimated using an acoustic method allowing ablation threshold and congruent ablation threshold estimation. The ablation threshold dependence on incident laser spot area and target density was studied also and recommends that the proper fluence has to be considered as a function of specific irradiation conditions. Plasma expansion analyses was performed in order to estimate the parameters that control the composition and energy of the ablated particles. Temporal and spatial resolved spectra were recorded and evidenced a high density of ionized species in the initial expansion stages, atomic emission being significant at late stages or in colder regions of the plume, where the oxide emission becomes also notable. Also a supplementary IR laser radiation focused in front of the plume for IR oxygen dissociation evidenced the oxidation enhancement at the interaction of the dissociation front with the plume species.

Based on the measured spectra of Raman scattering, we obtained the data concerning the modification of the microstructure of silicon film synthesized with the use of the LCVD (laser chemical vapor deposition) method on amorphous glass substrate. Appearance of a polycrystalline phase of silicon was observed when the initial amorphous film was irradiated with high-power light pulses of a CO₂ laser. Time resolved reflection spectra were measured for irradiating silicon films in situ. Was observed the polycrystalline film formation, moreover, films melting was not founded.

The free expansion evolution of cooper plasma produced by laser ablation is studied by the analysis of the angular distribution and space evolution of the deposition rate and time-of-flight measurements (TOF). The angular distribution of the neutral and ionic species is mainly frontal, but the angular distribution of the neutral species is broader than that of the ionic species. The total number of species, ion dose and most probable ion energy (by solid angle) show no evolution at distances between 7 and 15 cm of the target indicating a global free molecular expansion. The TOF measurements show that the energy distribution of plasma species is different in different directions. Using the Saenger approximation it has been calculated the temperature and velocity of the different ions present in the plume. An increase of the species temperature in the plasma expansion has been observed. The different results obtained by the global measurements and TOF measurements are discussed analyzing the limitation of the Saenger's model and considering the electron-ion coulombic interactions.

We realized three different configurations for the production of picoseconds pulses in the UV by a diode-pumped solid-state laser. The first one is based on a diode-pumped Cr:LiSAF oscillator delivering tunable picosecond pulses in the near infrared. A Ti:Sapphire regenerative amplifier increased IR pulses energy up to 4.5 (mu) J. After doubling and tripling in two LBO crystals, we obtained pulses with an energy up to 0.14 (mu) J tunable between 273 and 286 nm. In the second scheme, based on a modelocked Nd:YAG laser, the SHG (KTP) and SFG (LBO) crystals are both inserted inside the cavity. The laser operated in a Q-switched mode-locked regime and produced 1.2 mW of UV average power in pulse of 60 picoseconds duration and 4 W peak power. In the last architecture, we used a resonant enhancement with a ring- cavity. We obtained 54% conversion efficiency in the green for picoseconds pulses at 1064 nm at 100 MHz rep. rate. A special arrangement was implemented for compensation of the birefringence and walk-off of the KTP crystal in the resonant cavity. Conversion to UV in the same cavity is in progress.

Our study concerns the coherent spatial shaping of lasers beams emitted by an excimer laser and was carried out in the optical laboratory of IRCOM. High power lasers in general and excimer lasers in particular are known for the poor spatial quality of their beams. In a conventional cavity (for instance built with two plane parallel mirrors and with a large Fresnel number), this kind of laser exhibits a powerful laser beam but in a wide divergence angle because of the large number of spatial transversal modes. This multimode beam provides an homogeneous time integrated illumination useful in surface processes applications. Such a kind of multimode beam is frequently called <<TOP HAT BEAM <<. For others applications like micro-machining or drilling we need a powerful and low divergence beam. That mean's this beam contains a low number of spatial modes and its divergence angle is closed to the diffraction limit in order to be focused in a minimal size spot. The brightness of this beam is higher than the brightness of the multimode beam. We have called this beam a << HIGHBRIGHTNESS BEAM <<. For this kind of applications we study a new method to produce an high brightness beam with minimum angular divergence A iE (according to the beam diameter D) using an excimer amplifying medium.

The multifrequency laser transmitter for high precision ranging and atmospheric sounding was developed. The system generates pulses in the picosecond region with the wavelengths of 1.06 micrometers , 0.53 micrometers , 0.35 micrometers , 0.63 micrometers and 0.46 micrometers .

An efficient all-fiber 1.53 micrometers high peak power and high repetition rate pulse laser source is presented. The first stage is a ring fiber laser principally including a short length of Er³⁺ doped fiber pumped by a 980/500 mW compact MOPA, and a short rise time acoustooptic modulator. Another length of a different Er³⁺ doped fiber pumped by a second MOPA works as an amplifying stage for the emitted pulses. With this optimized source, 30 ns/1 kW triangular pulses at 10 kHz, with a stability better than 0.2% have been obtained. This corresponds to a conversion efficiency of the optical power from the pump to the pulses reaching 30%. These performances make this source very suitable for eyesafe range finding and free space communications. Thanks to its robustness and compactness due to its all-fiber design and to the use of small size pump MOPAs, this source is well-adapted for portable field applications.

Short high power pulses can be generate from a laser cavity by passive mode-locking. Previously, saturable absorbers were used, but recently nonlinear mirrors have simplified the laser cavity maintenance. The optimization of the performances of this component in function of the angle (alpha) between the direction polarization of the incident wave and the ordinary axis of the nonlinear crystal is reported.

Transmission of XeCl excimer laser pulses through commercial silica optical fibers with high OH content have been investigated. The Ultraviolet irradiation of these optical fibers includes color center generation and two photon absorption in the fiber core. These absorbing centers disappear at room temperature. A spectroscopic study of fiber core fluorescence permitted to clearly identify the Non Bridging Oxygen Hole Centers as main type of defects created. The influence of laser parameters on transmission evolution of the optical fiber observed during irradiation are discussed. The use of a bundle of fibers to transmit high average power excimer laser is presented. The results obtained in these experiments are promising for the use of optical fibers in a wide range of excimer laser industrial applications.

This paper presents a review of our theoretical work on non- linear magneto-optical properties of semiconductor quantum wires. We have studied both second- and third-order non- linearities. The former arises from dipole transitions within the quantized magneto-electronic subbands in a quantum wire, and the latter arises from phase-space filling and saturation of the excitonic state followed by the formation of biexcitons. A magnetic field causes non-zero second-order non-linearity in a geometrically symmetric quantum wire by breaking inversion symmetry and inducing forbidden transitions between electronic subbands. It also enhances third-order non-linearity by adding magnetostatic confinement to the spatial and dielectric confinement of excitons and biexcitons, thereby further constricting the phase space for these entities. Additionally, we find that a magnetic field can be used to modulate the non-linear differential refractive index and absorption coefficient of quantum wires thus allowing efficient polariton transport, optical waveguiding without a concomitant high absorption or insertion loss, and the possibility to realize magneto- optical devices such as frequency modulators, tunable couplers, limiters and mixers.

Nonlinear optical absorption at discrete frequencies has been observed in semiconductor quantum wires crystallized in transparent dielectric matrix (inside chrysotile asbestos nanotubes). The induced changes of absorption in quantum wires have been explained by phase space filling, quantum- confined Stark effect and screening of excitons; filling of the size-quantized energy bands with nonequilibrium carriers (dynamic Burstein-Moss effect); renormalization of the 1D energy bands at high density of the induced plasma. The measured values of exciton binding energies are much greater than that of the corresponding bulk semiconductors. The increase of the exciton binding energy may be attributed not only to the quantum confinement but also to the `dielectric confinement'--to the increase of electron-hole attraction because of the difference in dielectric constants of semiconductor nanowires and dielectric matrix.

Raman spectroscopy is employed for structural characterization of BaTiO₃ ferroelectric thin films, deposited by a hybrid DC-field enhanced pulsed laser deposition process. Pulsed excimer laser radiation (KrF, (lambda) equals 248 nm, (tau) equals 25 ns) is used for material removal from a sintered BaTiO₃-target in an O₂ processing gas atmosphere (pressure p(O₂) approximately equals 1 * 10^-1 mbar) with subsequent deposition on a substrate. Additional energy is supplied to the laser- induced plasma via a system of two concentric ring electrodes lying on different electric potentials (difference (Delta) V up to several hundred V), leading to further activation of the plasma and ignition of a DC- discharge in the processing gas atmosphere. Micro-Raman spectroscopy is performed with Ar⁺ laser radiation ((lambda) equals 488 nm), using a microscope unit to achieve a high spatial resolution in the range of 1 micrometers . The Raman spectra of the BaTiO₂ films show peaks typical for the tetragonal/cubic Perovskite structure. Polarization- dependent measurements reveal a mean c-axis orientation normal to the substrate surface, regardless whether a DC- field is applied or not. Using low DC-bias voltages ((Delta) V equals 50 V) allows lowering the substrate temperature without affecting the crystal quality of the films, as determined from the full width at half maximum of the Raman peaks, which is a measure for the crystal quality. High DC-bias voltages ((Delta) V equals 700 V), however, lead to amorphous films. The dielectric constant of the BaTiO₃ films is strongly correlated to the crystal quality.

We discuss the mechanism of efficient photoluminescence (PL) from Si nanocrystals. Luminescence properties of SiO₂- capped Si nanocrystals are different from those of H- passivated Si nanocrystals. The size-dependence of PL properties and resonantly excited PL spectra of SiO₂- capped Si nanocrystals indicate that excitons are localized at the interface between c-Si and SiO₂ surface layer. The TO-phonon related structure in resonantly excited luminescence is clearly observed in H-passivated Si nanocrystals. H-passivated Si nanocrystals show their crystalline nature, while the oxidized Si nanocrystals show their disorder nature. The luminescence properties of Si nanocrystals are discussed.

Spatially and temporally varying neutral, ion and electron number densities have been mapped out within laser ablated plasma plumes expanding into vacuum. Ablation of a magnesium target was performed using a KrF laser, 30 ns pulse duration and 248 nm wavelength. During the initial stage of plasma expansion (t <EQ 100 ns) interferometry has been used to obtain line averaged electron number densities, for laser power densities on target in the range 1.3 - 3.0 X 10⁸ W/cm². Later in the plasma expansion (t equals 1 microsecond(s) ) simultaneous absorption and laser induced fluorescence spectroscopy has been used to determine 3D neutral and ion number densities, for a power density equal to 6.7 X 10⁷ W/cm². Two distinct regions within the plume were identified. One is a fast component (approximately 10⁶ cm^-1) consisting of ions and neutrals with maximum number densities observed to be approximately 30 and 4 X 10¹² cm^-3 respectively, and the second consists of slow moving neutral material at a number density of up to 10¹⁵ cm^-3. Additionally a Langmuir probe has been used to obtain ion and electron number densities at very late times in the plasma expansion (1 microsecond(s) <EQ t <EQ 15 microsecond(s) ). A copper target was ablated using a Nd:YAG laser, 7.5 ns duration and 532 nm (2 (omega) ) wavelength, with a power density on target equal to 6 X 10⁸ W/cm². Two regions within the plume with different velocities were observed. Within a fast component (approximately 3 X 10⁶ cms^-1) electron and ion number densities of the order 5 X 10¹² cm^-3 were observed and within the second slower component (approximately 10⁶ cms^-1) electron and ion number densities of the order 1 - 2 X 10¹³ cm^-3 were determined.

The laser induced plasma plume expansion in vacuum is studied by a Monte Carlo simulation. The global shape of the plume created above a copper target is followed in time by using a 3D algorithm. An original method has allowed the simulation with no restrictions on laser spot width or ablated depth. Particles evaporation from the sample surface during the laser pulse is done by introducing in the model a radial distribution of laser energy and a high surface temperature induced by the vapor pressure. The effects of the later energy absorption by the evaporated particles appear to be dominating parameters on the expansion process. An approximation of these effects has been done by considering a fraction of energetic species, corresponding to the recombination of ionic species by kinetic energy transfer in the cloud. Results of this simulation are compared with experimental results obtained by time of flight measurements and fast photography of the luminous component of the plume.

In order to get a better inside in the reactive Pulsed Laser Deposition of nitride thin films, we performed time- and space-resolved plasma diagnostics during ablation of Ti, Al and C targets in low pressure nitrogen containing atmospheres using pulsed nanosecond UV lasers. In the case of carbon, thin films of C_xN_y were deposited on silicon substrates and characterized by Rutherford Backscattering Spectroscopy and Nuclear Reaction Analysis. With respect to irradiation of metal targets, during which a dense and highly ionized plasma was induced for laser intensities >= 100 MWcm^-2, much higher values >= 1 GWcm^-2 were necessary to induce significant plasma ionization on carbon. To increase the plasma reactivity in the case of carbon ablation, a radiofrequency discharge was added to excite and preionize the ambient gas. From correlation between the plasma characteristics and thin film analyses, conclusions could be made about the C_xN_y deposition process.

Surface plasmons, excited in thin metal films by means of laser irradiation, can be used as a very sensitive probe to study a wide variety of processes at surfaces and interfaces. We give here an overview over some recent applications. Examples are adsorption and desorption phenomena of physisorbed films, which can be studied with high temporal resolution on a nano-second scale. Another application is the sensitive detection of changes in the optical properties of thin films, e.g. of photo-chromic materials. Furthermore, surface plasmons can be used to monitor pressure variations on short timescales, and are thus suitable, e.g., for investigating and characterizing shock waves impinging onto liquid-solid interfaces. The surface plasmon technique can also be utilized for imaging the lateral structure of a patterned surface with a resolution on the order of a few microns. Surface plasmon spectroscopy is thus a very versatile tool for surface and interface diagnostics.

We use x-ray laser interferometry to probe defects induced by a strong electric field on niobium surface. Niobium has been chosen on account of its frequent use in superconductive cavities of particle accelerators. The x-ray laser emits bright, 50 ps-duration pulses at (lambda) equals 21.2 nm. The beam is reflected on the niobium surface under grazing incidence. The interferometer is of the wave-front division type. Interferograms are single shot recorded, which enables to probe `instantaneous' defect morphology. We observed appearance and evolution of defects between 14 MV/m and 35 MV/m. The vertical set amplitude is of 10 - 20 nm. The defect structure has been observed to shift by 500 micrometers along the metal surface under a constant 35 MV/m electric field, during the 20 minutes time interval between two laser shots.

We have shown that the surface spatial soliton formation is possible near the interface between a photorefractive crystal with a drift and diffusion nonlinearity and linear dielectric or metal. The zero order soliton shape is essentially asymmetric due to the diffusion nonlinearity. The N-th order soliton solution looks like a sequence of decaying antiphase peaks.

The effect of fluorescence saturation is caused by limited life-time of molecules in excited state, and appears as a non-linear dependence of detected fluorescence signal versus excitation intensity under laser pulsed irradiation of the sample. It is noticeable at conditions of 10²⁴ exciting photons per second per square centimeter, which we usually have for laboratory laser fluorimeter. Spectroscopy of saturated fluorescence is a promising tool for studying such spectral molecular characteristics, as fluorescence life- time, absorption cross-section, constant of singlet-singlet annihilation, and their changes due to molecular interaction. The work presents the theory of the effect considering the cases of different intermolecular interaction (quenching mechanisms, singlet-singlet annihilation) and describes the experimental results on florescence saturation for several organic dyes in water.

Laser surface processing is a promising technique for alloying and synthesis of wear resistant coatings. To this end, commercially pure titanium was laser gas-alloyed with a mixture of nitrogen and carbon monoxide, and the influence of processing parameters was studied. The surface treatments were performed using a 400 W Nd:YAG pulsed laser. The composition of the gas mixture was set at either 100% N₂, 67% N₂ + 33% CO, 50% N₂ + 50% CO, 33% N₂ + 67% CO or 100% CO. The microstructure of the reacted layer of specimen was studied by optical and scanning electron microscopy. Their thickness was characterized and surface hardness profiles were determined. X-ray diffraction, Auger electron spectroscopy and X-ray photoelectron spectroscopy were used for determination of crystalline structure and chemical composition of phases. The study of processing parameters such as incident power density, pulse length and pulse rate showed that the optimum conditions for wear resistance were influenced by the composition of the gas mixture. Abrasive and erosive wear tests on laser-treated surfaces showed a substantial improvement in wear resistance over untreated titanium. This reduction in wear rate is attributed to the formation of the hard compounds TiN, TiCO and TiCNO in the resolidified layer.

We made the model calculations of the surface photoeffect in bichromatic laser field with controllable phase difference between field components. It is shown that the photocurrent phase modulation may be quite pronounced at the reasonable values of the laser intensities and frequencies. Photocurrent dependencies upon a number of involved parameters are investigated in details. Present calculations may be of interest for the laser thin film technologies and optical surface diagnostics.

We have observed visible photoluminescence (PL) from F-doped silicon nanocrystallites films prepared in the chemical vapor deposition system. The PL spectra are in the range of 500 - 800 nm with the luminescence peak localized near 540 nm. High energy shift of the luminescence peak is discussed in terms of material structural characteristics, and a tentative explanation of light emission mechanism is proposed.

Method of relative deviation plot of line intensities for LTE presence verification and excitation temperature determination is suggested and analyzed. This method seems to be attractive as it does not require the values of the Einstein constants A_ji of spontaneous emission.

The processes of the electron excitation energy transfer (EEET) between the cation dye molecules in aqueous polymer solutions have been studied. The dependencies of the efficiency of EEET between dye molecules were received experimentally. We have found that the distribution of the interacting molecules in the investigated systems had a fractal character. The fractal dimension of the investigated systems have depended on the concentration of surfactants and polyelectrolytes.

We have investigated the craters created after high intensity visible and UV-laser pulse interaction with the metal surfaces in air. The experiments were performed on different pure metal samples in the intensity range typical for laser plasma analytical application experiments with nanosecond laser pulses. The craters were characterized by their depth, diameter and volume. The analysis and discussion of the obtained results are presented.

Laser ablation of pure metals by femtosecond, picosecond and nanosecond pulses is studied in air at atmospheric pressure. Craters created after interaction of visible and UV laser pulses with the targets are investigated. The dependence of the ablation efficiency in terms of ablated volume per unit of energy on the pulse duration is discussed.

Dynamics of nonlinear interferometer with optical feedback was analytically and numerically studied. Mathematical model of the system was elaborated. Linear stability analysis in the sense of noise in the input field was carried out. Numerical simulation results were presented.