The main results of experimental investigation of basic physical, spectroscopic and laser properties of Nd:GdVO₄, Nd:YVO₄, Nd:LaSc₃(BO₃)₄, Tm:GdVO₄ and other oxide crystals are discussed. The problem of obtaining of high efficient CW lasing on fundamental and second harmonic wavelengths using optimized laser resonators including microchip configuration is studied.

To change the intensity distribution of the fundamental mode in a Nd:YAG laser resonator to a top-hat profile we developed and used a dielectric graded-phase mirror. A super-Gaussian mode of the sixth order was generated by means of a graded-phase mirror with a simple ring-shaped phase step on a spherical reflector. The depth of the ring was 90 nm. The graded-phase mirror was manufactured with an ordinary vapor deposition technique. An annular mask with a thickness of 10 μm was used to avoid the deposition of the LaF₃ vapor at the position of the ring. Laser experiments with continuous-wave and repetitively pulsed dioed-laser pumping were performed and compared. The results are in excellent agreement with the theory.

Thermally induced optical effects can be exploited to generate adaptive optical devices such as self adjusting lenses. A liquid or gel layer sandwiched between two laser rods can self-adaptively compensate for the thermal lenses in the laser rods and therefore significantly increase the power range and the output beam quality of high-power lasers. Thermo-optically self-compensating amplifiers and their influence on optical resonators are discussed.

The interaction area of high-intensity tightly-focused 1078 nm pulses of 30 ps duration with CVD diamond film has been studied using second harmonic (540 nm, 20 ps) unfocused beam for backlighting. The 2D spatial distribution of energy density of probe radiation passed through the tested sample was recorded that allowed to measure the transient relative transmittance of the laser-affected zone as a function of temporal and spatial coordinates. The pump-probe interferometric measurements of laser induced refractive index in fused silica glass done with micron spatial and picosecond temporal resolution are also presented and discussed.

First results and analysis of second harmonic generation with a Nd:YAG laser working in the long pulse, free running mode are presented in this paper. Second harmonic generation conversion efficiencies of up to 17.5% and pulse powers of 162W have been generated with a free running Nd:YAG laser and a KTP non-linear crystal. The conversion efficiency is limited by a saturation effect and optical damage occurring at ~50 times lower peak intensities than in the Q-switch mode. The saturation and damage mechanism involves creation of temporary 'color centers' induced by the second harmonic radiation and subsequent increased fundeamental wave absorption.

Laguerre-Gaussian (LG) laser modes (annular shaped modes with helical phase fronts) are used to both manipulate and cut microscopic particles. We use holographically produced LG laser modes to manipulate microscopic bubbles. Interference patterns formed from LG modes of opposite phase helicity are used to create 3D structures and to continuously rotate glass rods. The technique of using and LG beam to create microscopic sections of chromosomes is described.

A non-steady-state theoretical and mathematical model and a complex of computer codes have been developed for modeling a high-power double-pass explosively pumped photo-dissociation iodine laser (EPDL) with phase conjugation (PC) at SBS. The model and the complex of codes taking into account 3D of space consist of two blocks. The first block is devoted to detailed modeling of the SBS mirror consisting of an angular selector of Stokes radiation, an ordered raster of small diffraction lenses, a main focusing lens, and a SBS cell. The second block describes the dynamics of radiation in the laser system as a whole with using SBS mirror parameters calculated in the first block. The model takes into account parasitic reflections of laser radiation from the elements of the optical scheme, intrinsic amplified spontaneous emission of the amplifiers, radiation losses in the optical path, non-uniformity of gain, and radiation refraction on optical non-uniformities of the active medium caused by a shock wave. As a result of calculations an optimal configuration of the SBS mirror has been determined, possessing unique properties if compared to the existing specimens of the SBS mirrors. It stably gives a nearly ideal quality of PC at any level of SBS saturation, i.e. any reflection coefficient that is confirmed by experimental laboratory investigations. Modeling of the laser sytem with two amplifiers at working mixture 25 Torr C₃F₇I+125 Torr Xe and amplifier aperture 15 cm has been shown a good agreement of calculated result with available experimental data in energy, time dependence of power and Strehl number of output radiation. The considered EPDL has output energy of about 400 J and brightness of about 1012 J/ster. Calculations show that under rising the density flux of input signal from the master oscillator in a range 0.01-20 W/cm², the brightness of the EPDL output radiation increase whereas the full energy varies relativley slightly. It is shown that parasitic reflections of laser radiation from the ends of amplifiers and elements of the optical scheme with a coefficient exceeding 10^-7 considerably decrease the axial brightness of output radiation. In order to reduce the harmful effect of parasitic reflections on brightness, the distance between the ampfiers should be increased.

In this paper we discuss some result achieved at Laboratoire d'Optique Appliquee that may improve the capabilities of the laser-produced plasma x-ray source for applications in the study of ultrafast transient structures.

Nd:YAG has favorable material properties to minimize the thermally induced lenses in lasers at cryogenic temperatures. In the present work we measured a significant reduction of the thermal lens in a Nd:YAG rod cooled with liquid nitrogen. The power range for stable fundamental-mode laser oscillation was demonstrated to be significantly enlarged at low temperatures. The experimental results were compared to analytical models and finite-elements simulations.

We report the obtaining of thin organic films based on poly(methyl methacrylate) polymer by Pulsed Laser Deposition on silicon substrates and quartz slides. The films were characterized by complementary techniques: x-ray Diffraction, x-ray Photoelectron Spectroscopy, Atomic Force Microscopy, Optical Microscopy, Raman Spectroscopy and Fourier Transform Infrared Spectroscopy. The obtained structures are amorphous. The film composition and structure depend on both the laser fluence as well as on the temperature of the substrate during deposition. We put in evidence in freshly deposited films the presence of diamond-like carbon while its amount strongly increases by annealing at ~400°C in Argon atmosphere.

Surface of soids play a leading role in any process of interaction between solids, solids-liquids, solids-gases and solids-plasma. Topology (roughness) is a key parameter of the solids surface which influence a lot of mechanical, optical, electronic, chemical, thermical and other characteristics. Nowadays, the laser-based technologies is a great challenge to improve a surface topology (ST) quality and controllability. Different laser-based surface treatments are considered: (i) surface microstructuring and control fo roughness by laser ablation, (ii) surface microstructuring based on creation of surface electromagnetic waves and surface periodic structures, (iii) surface smoothening and microstructuring based on laser heating until melting and further phenomena in a melted phase. Some examples of laser applications to improve optical, tribological and other surface characteristic are considered and analyzed. Future prospects of this field are discussed.

Ultrashort pulses appear very promising for material removal with ultra high precision. Initial investigations showed, however, several unexpected quality problems such as formation of recast, ripples and irregular hole shapes even in the femtosecond pulse regime. After describing the problems, this contribution will present some progress in fundamental understanding of the ultrafast ablation process. On the basis of this knowledge technical means have been developed allowing to achieve an unprecedented level of accuracy at acceptable expenses. The latter being strongly influenced by the shortness of the laser pulse, a comparison between pico- and femto-second regime will be presented.

A high-resolution laser radar has been developed for laboratory applications at an accurate 3D reconstruction of real objects. The laser scanner can be used to produce single cylindrical range image when the object is placed on a controlled rotating platform or, alternatively, 3 or more linear range images, in order to fully characterize the surface of the object as seen from different points of view. From the sample points, characterized by an uncertainty as small as 100 μm, the complete object surface can be reconstructed by using specifically developed software tools. The system has been successfully applied to scan different types of real surfaces (stone, wood, bones) with relevant applications in industrial machining, artwork classification and medical diagnostics. Significant examples of 3D reconstructions are shown and discussed in view of a specific utilization for reverse engineering applied to artwork restoration and medical prosthesis.

Laser-induced structure transformations in diamond single crystals implanted with light ions (H⁺, D⁺, He⁺) are studied by monitoring changes in the material density and optical transmission in dependence on UV laser pulsed irradiation parameters and ion implantation conditions. Characteristic features of the processes of laser annealing, graphitization, low-rate etching and explosive ablation of ion-implanted diamond layers are discussed.

This work is relevant to the development of a precision velocimeter for a self-powered robotic vehicle designed for operation in the Antarctic Regions. This is a crucial problem because of the difficulty to measure the velocity with appropriate accuracy under slip conditions and in the absence of reliable reference points over vast snow or ice fields. Speckle velocimetry is expected to provide fairly accurate measurements under Antarctic conditions. The results of early theoretical and experimental studies on the problem are very encouraging.

We present the experimental results concerning the study and the development of a Laser Ion Source (LIS). By means of an excimer laser we irradiated a metal target at high power density, realizing an efficient source of multiple charged ions. The analysis of the generated plasma plume was performed for three different laser spot sizes determining the threshold conditions of the ablation process. A diagnostic system with a Faraday cup was developed in order to detect the ion current along the propagation tube. Time-of-flight measurements were performed, also inserting in front of the cup an adjustable voltage electrostatic barrier in order to get quantitative information about the ion flux and the kinetic energy of the produced ions. To study the plasma characteristics we evaluated the total etched material per pulse, 0.25 μg, and the fractional ionization, 12%. A modified Maxwell-Boltzmann distribution was applied to provide a consistent description of the velocity distributions in the plume. The ablated material was spatially monitored by optical transmission analysis of a deposited film. Applying the high voltage to the LIS extraction gap, an ion beam containing Cu+1 (0.44mA), Cu+2 (0.34mA), Cu+3(0.99mA), and Cu+4(0.01mA) ions was obtained.

The technology of target production was developed and the regimes of their irradiation was determined. The investigation was made of electrofield emission characteristics of thin nanodiamond and glassy carbon films deposited by laser ablation of diamond and glassy carbon targets. X-ray analysis and Raman spectroscopy showed that there was no phase change in the target substance during the process of the target substance deposition upon the substrate. Emission currents up to 10 mA/cm² in the field of 20 V/μm were obtained. The numerical simulation of temperatire fields distribution in the target material was carried out.

An essential problem of the quantum information systems is the controllability and observability of the quantum states, generally described by Lindblad's master equation with phenomenological coefficients. However, in its general form, this equation describes a decay of the mean-values, but not necessarily the expected decaying transitions. We propose a quantum master equation with microscopic coefficients where these transitions are correctly described, and investigate the properties of the dissipative coefficients. Being of Lindblad's form, this equation preserves the quantum-mechanical properties of the density matrix during the whole evolution of the system and is in accordance with the entropy principle. On this basis, generalized Bloch-Feynman equations with microscopic coefficients for N-level systems are obtained.

We present a novel optical system (patent pending), which makes homogeneous the spatial energy distribution of a light beam, independently of the local intensity fluctuations strength. It can also change the spot dimensions of the homogenized beam over a large range of values without replacement of any optical element and without changing the length of the radiation path.

New studies concerning the performance of Pd films embedded with hydrogen are presented. The films were realized on Si wafers by thermal evaporation and soaked in hdyrogen for different days. Every experiment processed two or more samples, one of which was irradiated by an excimer laser the day before its analysis. The laser fluence was lower than 25 mJ/cm² in order to avoid the film ablation and the maximum gas pressure was 5 bar. The samples were analyzed by scanning electron microscopy and an electron microanalysis. Just after four processing days the films showed a morphological modification while with more than eight processing days new elements were observed, Na, S, Ca nd Rn. The found elements were absent in the no-treated samples.

Experimentally we observed stochastic resonance-like (SR) phenomena of diffusion transport of silica microspheres in water solution in the spatially distributed potential created by Bessel light beam. One-dimensional approximation of this optical field is periodic potential of washboard type with static force applied. We observed two distinguished types of SR--enhanced particle mobility in the direction of static force and a cooperative behavior of self-ordering patterns.

Ultrafast laser ablation of metals has been studied by microscopy investigation of the laser produced craters. The crater depth has been measured as a function of laser pulses and fluence. The result are compared to a analytical model describing the laser-matter interaction in the femtosecond regime.

Polycrystalline SiGe is attracting more and more attention in micro and optoelectronics devices both at industrial and university level. Research on both devices and material growth techniques continues at a very rapid pace in the scientific world. Low cost production techniques, capable to produce such alloys with uniform and controlled grain size, becomes of particular attention. Excimer laser crystallization has proved to be a valuable how thermal budget technique for amorphous silicon crystallization. Its main advantages are the high process quality and reproducibility joint to the possibility of tailoring the grain sizes both in small selected regions and in large areas. This technique is here applied for producing poly-SiGe alloys from amorphous SiGe films deposited on glass.

It is found that the intensity of resonant light scattering in the region of excitonic transitions in GaAs/AlGaAs quantum-well structures is modulated strongly (up to 40% under our experimental conditions) upon additional pumping of the structure by radiation with the photon energy exceeding the band gap in the barrier layers. The effect observed originates from the redistribution of the oscillator strengths of the excitonic transitions due to the formation of charged three-particle complexes (trions) made possible by the accumulation of nonequilibrium charge carriers of one particular sign (holes in our case) in the quantum wells upon above-barrier pumping.

The production of ethylene by ionzing radiation induced effect in a living organism is described. The photoacoustic detection of ethylene traces and the experimental set-up are illustrated. Experimental results on the photoacoustic measurement of ethylene released in the breath by mice exposed to x-ray beam are reported.

We demonstrate fabrication of 2D photonic crystal structure inside the volume of SU-8 resist by four beams interference. This structure, actually, is a 3D structure fabricated inside the film without sample scanning laser beam steering. The mechanism of recording in transparent dielectrics is discussed in terms of third harmonic generation, white light continuum, and thermal emission by "hot" electrons.

We demonstrate fabrication of two-dimensional (2D) photonic crystal (PhC) structure inside the volume of SU-8 resist film by four beams interference. This structure, actually, is a 3D structure fabricated inside the film without sample scanning or laser beam steering. The mechanism of recording in transparent dielectrics is discussed in terms of third harmonic generation, white light continuum, and thermal emission by "hot" electrons.

In order to compensate for thermally induced lenses we have recently proposed and successfully demonstrated a new self-adaptive compensation scheme for transversally pumped laser rods. Now we show how this scheme can be simplified and adapted for end-pumped laser rods. The method is demonstrated with an end-pumped Nd:YAG laser and preliminary experimental results are presented.

In contrast to flashlamps the emission of single stripe laser diodes is highly directional and can be focused rather easily to small spots, which gives access to very high pump intensities. Numerical arrangements are possible for transferring the pump radiation to the solid state laser media. In this paper the most important concepts of diode laser systems for pumping solid state lasers are summarized and described. Thereby the aim is to find the most efficient and powerful method for endpumping a Yb³⁺-double clad fiber.

The optical excitation of the I6 level in Yb:Ho:YLF is studied. Pumping with a wavelength of 953 urn populates the 2F572 upper level of yi3+fromwhere the energy is efficiently transferred to the '6upper laser level ofHo3. Pumping is performed with a Ti:sapphire laser. Based on the measured rise times and decay times of the fluorescence from the y3 2F level, the Ho3 5S2 and '6 levels the cross relaxation coefficients w yi3+ 2F512 + Ho3 '8 —3 y132F712 + Ho3 '6), w (Ho3I6+ Ho3 '6 Ho3 5S2 +Ho3 '8) and w 2F512 + Ho3I8 y3 2F712 + Ho3 5S2) as well as the ESA cross-section o6 (Ho3 '6 — H35S2) are estimated with the aid of a numerical analysis

We report for the first time on the excimer laser (λ=248 nm) irradiation of siloxane-based flexible silicone rubber. Samples are investigated before and after laser treatment using optical microscopy, profilometry, SEM and Raman spectroscopy. Photodecompsition of silicone results in volatile organic radicals, Si clusters and sub-stoichiometric silica foam that develop on a rather chaotic surface topography. This novel medium is further exploited inducing selective auto-catalyzed metalization of the once-irradiated sample surface.

In this paper we present the experimental results and analysis of amorphous silicon nanoparticles (a-n-Si) optical properties. The optical properties of individual particles of a-n-Si imbedded in glycerol, water and conglomeration of particles have been studied. The optical absorption spectra for each nanocomposites measured in the spectral range from 300 to 1100nm differs much one from another, because it depends on the surrounding media, mainly, but not on the particles microstructure. This character of optical absorption in the visible range is defined by the double charge layer near the surface inside of the particles. The mechanism of the optical absorption is the composition of absorption by the surface electrons plasma waves and valence electron in strong static electric field created by double charge layer.

A simple method for obtaining a nearly Gaussian laser beam from a high order Hermite-Gaussian mode is presented. The method is based on separating the equal lobes of the high order mode and combining them together coherently. The method was experimentally verified with an arrangement of three mirrors, a 50% beam splitter and a phase tuning plate. The beam quality factor calculated in x-direction for the resulting output beam is 1.045, being very close to that of ideal Gaussian beam. The calculated power leakage is only 1.5%. The experimental near-field and far-field intensity distributions of the output beam have nearly Gaussian cross sections in both the x and y directions, with M²_x=1.34 and M²_y=1.32. With some modifications, it is possible to obtain an output beam with M²_x=1.15 and no power leakage.

We report on the experimental study of the excitation mechanism of fluorescence in a 10000-ppm wt. Tm⁺³-doped ZBLAN fiber. UV (at 365 nm), visible (at 453, 480 and 650 nm) and near infrared (~800 nm) radiation was observed under excitation at 1.064 μm. The responsible up-conversion mechanisms are investigated based on experimental data. The results show that the ³H₄ and the ¹D₂ levels are predominantly excited by ion-ion cross relaxation processes.

The influence of aluminum co-doping and CO₂-laser processing on the fluorescence lifetime of neodymium doped sol-gel derived silica glasses has been studied. The combination of host material modification and thermal treatment offers a possibility to overcome the limitations set on the fluorescence lifetime of Nd³⁺-doped silica by clustering, concentration quenching, and phonon quenching. Our study focuses on the fluorescing behavior of the produced samples depending on different methods of thermal annealing and host material modification. We show that neodymium doped sol-gel derived silica glasses, modified with aluminum and treated with a CO₂-laser exhibit a fluorescence lifetime of several hudnred microseconds at high dopant concentrations (e.g. 280±6μs for a Nd³⁺-concentration of 1.1×10²¹ cm^-3).

Using pulsed near infrared laser radiation for selective laser sintering bears several advantages compared to cw sintering such as low requried average power, less residual heat and improved lateral precision. By adapting the pulse length (and thus the heat diffusion length during the pulse) to the grain size of the used metal powder, the laser pulse energy can mainly by deposited in the skin of the powder particles where heating and melting is obtained, whereas the centers of the grains remain at much lower temperature and act as heat sinks after consolidation. The model described here was numerically implemented and experimentally tested with a pulsed Nd:YAG laser on titanium powder. The results of the model predictions and the performed experiments are in good agreement.

Controlled ablation of GaN, sapphire and SiC was investigated using both nanosecond and femtosecond laser pulses. Well-defined patterns of feature size ~10s of microns were successfully machined by fs pulses in all materials. Nanosecond (355nm) machining was primarily successful in machining GaN. Results for the different materials and pulse duration regimes are compared and contrasted.

Pulsed-laser deposition is a unique technique that has been employed for thin film growth of a broad variety of materials. Tuning of deposition parameters allows to produce advanced thin films with optimized materials properties. We report on the deposition and characterization of various kinds of high-temperature superconducting thin films and of ceramic/polymer composite layers.

Highly accurate resistances can be made by iteratively laser inducing local diffusion of dopants from the drain and source of a gateless field effect transistor into the channel, thereby forming an electrical link between two adjacent p-n junction diodes. Using transmission electron microscopy, we showed that the laser induced diffusible resistance can be performed without any structural modification to the microdevices. Current-voltage (I-V) characteristics of these new microdevices are shown to be linear at low voltages and sublinear at higher voltages where carrier mobility is affected by the presence of high fields. A process model involving an approximate calculation of the laser melted region in which the dopant diffusion occurs has been developed. Experimental results are well described by the proposed model.

The mode structure of supercontinuum emission generated by 40-fs pulses of 800-nm Ti:sapphire laser radiation in fused silica microstructure fibers is experimentally studied. The long-wavelength and visible parts of supercontinuum emission are shown to be spatially separated in microstructure-fiber models. With an appropriate spectral filtering, bell-shaped modes of the long-wavelength section (~720-900 nm) of the supercontinuum generated in a microstructure fiber with a small core diameter can be separated from either doughnut-like or bipartite modes of the visible part (~400-600 nm) of this supercontinuum. This effect can be employed to spectrally slice single modes of supercontinuum emission from microstructure fibers.

Laser-induced ignition of methane-air mixtures of varied composition was investigated experimentally using nano-second pulses generated by Q-switched Nd:YAG lasers (wavelength 1064 nm, 532 nm and 355 nm) at initial pressures up to 4 MPa. The minimum focal spot diameter was found to be about 20 μm for effective ignition, independent of the laser wavelength, indicating that small impurity particles provide the seeds for laser plasma generation. The minimum laser pulse energy needed for ignition ranged from 2-15 mJ decreasing reciprocally with initial pressure and with fuel equivalence ratio Φ in a mixing of Φ=0.91 to Φ=0.56. Corresponding threshold intensities ranged from 10¹⁰ to 10¹¹ W/cm². In this way, evidence for a non-resonant breakdown mechanism was established. Optical in-situ diagnosis of water vapor concentration covering the whole timespan of the combustion process in a stationary high pressure vessel with four optical windows was performed involving linear absorption measurements over the entire spectral absorption linewidth by rapidly tuned diode laser radiation at 2.55 μm. Additionally, planar laser-induced fluorescence was measured in a time-resolving fashion yielding 3D determination of the OH concentrations during the process. To the knowledge of the authors, these are the first results on laser-induced ignition under laboratory conditions well above atmospheric pressure being relevant for several technical combustion systems.

We report on the deposition of thin transition metal nitride (TMN) films by ablating Mo, Ta, V and W targets in low-pressure (1, 10 and 100 Pa) nitrogen atmosphere by KrF excimer laser pulses, and on their characterization. The targets were foils of high purity (99.8%). 3" Si(111) wafers wre used as substrates. Film characteristics (composition, crystalline structure, hardness) were studied as a function of N₂ pressure, KrF laser fluence (4.5-19 J/cm²), substrate temperature (20-750°C) and target to substrate distance (30-70 mm). Rutherford backscattering spectrometery (RBS) was used to calculate thickness of the films and identification of the composition. TMN films ar formed already at low N₂ ambient pressures (1 Pa) and laser fluences (6 J/cm²) on substrates at room temperature. XRD investigations show that films deposited at elevated temperatures are mostly polycrystalline. While Mo, W and Ta nitrides show respectively a γ-Mo2N, β-W2N and δ-TaN phase in almost any deposition condition, vanadium nitride shows a prevalent phase of δ-VN at N₂ pressures of 1-10 Pa, while at higher pressures (100 Pa) and at relatively high laser fluences (16-19 J/cm²) the dominant phase is β-V2N. Generally the crystallinity of the films improves by increasing the substrate temperature. Well-crystallinzed films are obtained on substrates heated at 500°C. Surface morphology, microhardness and electrical resistivity of the films are discussed as a function of both the nitrogen pressure and substrate temperature.

CO₂ laser beam scanning method was used for marking of organic materials (leather, paper, wood) both in continuous wave and in pulsed regime. The computer controlled X-Y galvometric scanner and the software developed for this application control every parameter of irradiation and allow programmable marking of simple marks, logos, alphanumeric characters, filled text, codes, graphics, or highly complex drawings and images. The factors influencing the quality of the marking were analyzed and the irradiation conditions were optimized to produce marks on organic materials with a quality imposed by industry standards.

We report on the fabrication of Ti:sapphire channel waveguides. Such channel waveguides are of interest, e.g., as low-threshold tunable lasers. We investigated several structuring methods including ion beam implantation followed by wet chemical etching strip loading by polyimide spin coating and subsequent laser micro-machining, direct laser ablation or reactive ion etching through laser-structured polyimide contact masks. The later two methods result in ribs having different widths and heights up to ~5 μm. By reactive ion etching we have obtained channel waveguides with strong confinement of the Ti:sapphire fluorescence emission.

Molecular methods of diagnostics of widespread diseases including vascular pathology on the base static and dynamic laser light scattering in serum blood solution are testified. The alterations of molecular parameters of blood serum of animal species (rats) after experimentally induced cerebral ischemia (hypoxia) and haemorrhagic stroke relative to controls were studied. It was obtained that effective mass of scattering particles in blood serum solutions is diminished for haemorrhagic and ischemic rats in comparison to control. The relative protein concentrations in blood serum also change both after false operation and in case of induced ischemia.

Investigations on the occurrence of structure and hardness changes (for two sorts of steel and for a hard metal substrate) in the immediate vicinity of laser induced craters are presented in this work. Experiments with femtosecond pulses were performed in air with a Ti:sapphire laser (800 nm, 100 fs) at mean fluences of 2, 5 and 10 J/cm². Series of microcraters were induced with 100 to 5,000 laser pulses per hole. Experiments with similar fluences, but 10 to 40 pules per hole, were performed on the same materials using a Nd:YAG delivering 100 ns pulese. After laser irradiation, cuts were made through the processed samples and the changes occurred in the crystalline structure of the target materials were evidenced by metallographical analysis of the resulting cross-sections. Hardness measurements were performed in points situated in the immediate vicinity of the laser-induced pores. Affected zones in the material surrounding laser induced pores were always found in the ns-regime, however with different properties for various laser parameters. In the fs-regime, zones of modified materials were also found and in such zones a significant hardness increasing was evidenced; the limit of the low fluences regime, where no structure changes occurred, was found to be slightly above 2 J/cm².

Laser cladding is a coating process which uses a laser beam to melt the coating material and a thin layer of the substrate to form a low dilution, pore- and crack-free coating, perfectly bonded to the substrate. The process may be used for large area coverage, by overlapping individual tracks, but it is the ability to protect localized ares and the wide range of materials that can be deposited that makes laser cladding particularly appropriate to tailor surface properties to local service requirements, opening new perspectives for surface engineering. Laser cladding has been finding widespread use for the protection of materials against wear, corrosion and oxidation, and for the refurbishing of components and tools. Other applications with considerable potential are materials development and synthesis and free-form near-net shape manufacturing. Examples of recent work will be presented and discussed.

The gaseous phase obtained by ablating a quasicrystalline AlCuFe target by nanosecond, piceosecond and femtosecond lasers, has been characterized by different techniques such as emission spectroscopy, quadrupole mass spectroscopy and ICCD imaging with the aim to study the plume composition, energy and morphology. To clarify the ablation process some films have been deposited, on oriented silicon, at different experimental conditions and analyzed by scanning electron microscopy, atomic force microscopy, energy dispersive x-ray analysis and x-ray diffraction. The results from nanosecond ablation show evidence of distinct albation mechanisms, which lead to different gas phase composition, as a function of the laser fluence. Films containing the quasicrystalline phase can be deposited only at fluences higher than about 6.5 J cm^-2 while at lower fluences the aluminum content exceeds the stoichoimetric values. The results obtained from femtosecond and picosecond ablation show that the processes in the short pulse regimes ar very different to the nanosecond one. In particular the plume angular distribution shows a characteristic high cosine exponent and the composition of the deposits is completely stoichiometric and independent from the laser fluence, even if to obtain quasicrystalline films a substrate temperature of 600°C is needed.

Laser irradiation of surfaces with short pulses in reactive atmospheres (nitrogen, methane) can lead to very effective nitrification and carburization via complicated laser-surface-gas-plasma-interactions. This laser nitriding and laser carburizing and their basic underlying phenomena will be presented and partly explained by results of example materials (iron, titanium, aluminum, silicon) where nitride and carbide coatings can be formed by fast and easily by Excimer Laser, Nd:YAG laser, Free Electron Laser and also by femtosecond Ti:sapphire laser. This implies laser pulse durations from the nanosecond to the femtosecond regime and wavelengths from ultra-violet to infrared. The resulting surfaces, thin films, coatings and their properties are investigated by combining Mossbauer Spectroscopy, x-ray diffraction, x-ray absorption spectroscopy, Nanoindentation, Resonant Nuclear Reaction Analysis, and Rutherford Backscattering Spectroscopy.

Laser nitriding of iron is an interesting phenomenon both in physics and industry. On the time scale of hundreds nanoseconds, high intensity (≈108 W/cm²) pulsed excimer laser irradiation on iron in nitrogen atmosphere produced a thin iron nitride layer (thickness > 400 nm) with a mean nitrogen concentration exceeding 10 at which greatly improves the iron surface mechanical properties and the corrosion or erosion resistance. Laser plasma/plume plays a crucial role in the complicated interplay of the laser-plasma-metal system. Since the nitrogen pressure is one of the most important parameters determining the laser plume dynamics, a nitrogen pressure series ranging from 0.05 bar to 10 bar is conducted. The characteristic parameters of the nitrogen depth profile are extracted and their pressure dependence is qualitatively discussed. By isotopic experiments in ¹⁵N and natural nitrogen environment, the evolution of the nitrogen depth profile during laser nitriding process is successfully traced. Both of the experimental results suggested that a 1D laser supported combustion wave model is reasonable to describe the lasers plume dynamics.

This paper reports on the potentialities of innovative lasers in microcutting of silicon, one of the most important materials in the field of microelectronics. In recent years, novel laser based micromachining methods have played an increasingly important role in the ongoing miniaturization of consumer electronics. Here, high-quality microcutting in silicon using a "green" laser, whose wavelength is readily absorbed by silicon, is presented.

This paper is devoted to analysis of correlation between surface microgeometry and tribological properties of friction pairs. Two experimental methods have been applied for surface microstructuring: vibrorolling and laser ablation. Dependence of different in-service characteristics on groove area has been done. Production examples are demonstrated. Preliminary comparison of laser and mechanical structuring is carried out.