It is considered photo-excitation, non-equilibrium heating and thermal after-action induced by super-short laser pluses interacting with metals. It is shown that classical model of thermal laser-induced destruction of metals should be corrected in the case when pulse duration is much less than characteristic time of energy transfer from electrons to the lattice. In particular, possible important role of laser- induced electric-physical processes should be taken into account.

We ablated Si, SIO and ITO targets in low-pressure O₂ with XeCl and KrF laser pulses at fluences of 5-8 J/cm². The films were deposited on Si and glass substrates at temperatures of 20-600 degrees C. The substrates were generally set parallel to the target. To reduce droplet deposition, some films were deposited in off-axis configuration or using the so-called 'eclipse method', characterized by a shadow mask between target and substrate. Dense, continuos ITO films with resistivity as low as 1.6 by 10^-4 (Omega) cm and a high transparency in the visible region were deposited. Ultra-thin films were deposited and successfully used as electrodes in optoelectronic devices. Dense, stoichiometric, thick SiO₂ films were deposited on substrates either at room temperature or heated at moderate temperatures. Droplet density and surface roughness are kept quite low by using special deposition configurations. It results that multi- component films like ITO and silica can be efficiently deposited by using the reactive pulsed laser deposition.

Photoelectrical properties of nonuniform semiconductor under IR laser radiation has been investigated theoretically and experimentally. It is shown that photoemission of hot carriers across the potential barrier and the crystal lattice heating are dominant mechanisms of the photovoltage formation in p-n and l-h junction when laser photon energy less than the semiconductor energy gap. Influence of aluminum arsenide model fraction in GaAs/Al_xGa_1-xAs p-n heterojunction on CO₂ laser radiation detection has been studied. It has been established that the photoresponse originating from the free carrier heating depends on the energy band discontinuities in heterojunction. GaAs/Al_xGa_z-xAs heterojunction with x <EQ 0.2 is found to be more suitable for IR detection compared to GaAs homojunction. In metal- semiconductor Schottky contact photoresponse demonstrates strongly nonlinear dependence on excitation intensity when photon energy is less than Schottky barrier height. We suppose that in this case the photosignal is caused by the multiphoton and multi step electron photoemission across the Schottky barrier.

We study the surface dynamics of silicon nitride films deposited by UV-induced low pressure chemical vapor pressure. Atomic force microscopy measurements show that the surface reaches a scale invariant stationary state coherent wit the Kardar-Parisi-Zhang (KPZ) equation. Discrete geometry techniques are oriented to extra morphological characteristics of surface and bulk which corresponds to computer simulated photodeposit. This allows to determine the physical origin of KPZ scaling to be al ow value of the surface sticking probability, and connected to the surface concentration of activate charged centers, which permits to start the evaluation of the Monte Carlo-molecular dynamics simulator.

The theoretical description of photochemical transformation process of glassy chalcogenide semiconductor films has bene developed. The effect of pulsed ArF excimer laser radiation on glassy chalcogenide semiconductor is analyzed. It is found that photochemical transformation of AsSe is characterized by optical sensitivity about 3 cm³/kJ and threshold radiation intensity about 17 kJ/(cm² sec).

The development of techniques of optical manipulation of matter attracts great attention. One of the most interesting mechanisms for such manipulation is the dielectric light- matter interaction. This point was used by R. Beth, in 1936, to demonstrate an angular manipulation of a birefringent uniform macroscopic object. We have proposed and developed a two-beam technique that is used for the manipulation of nematic liquid crystal materials. Pertinent external control parameters, such as the mutual polarization of the two beams, the ratio of the two beams' intensity, the total intensity and the interaction geometry, are pointed out. Effective optical control via the non-resonant angular momentum transfer to the cluster of illuminated molecules is predicted and realized experimentally. In particular, it is shown that quasi-uniform precession regimes may be light- controlled at 100 percent. Moreover it is shown that the circularly polarized light-induced breakdown of orientational symmetry in non-chiral liquid crystal may result in their macroscopic chiral organization. Stationary, precessing and oscillating chiral modes are observed which may be controlled via the above mentioned external parameters. Consequently, since the non-planar deformations are at the origin of the multi stability of the system, it is expected from the theory that some important features of the isothermal light-induced phase transition should be continuously light-driven, without breaking the circular symmetry of the excitation beams. We believe that our two- beam technique is not restricted to the field of liquid crystal and may be also applied in biophysics, where living entities should play the role of the non-absorbing and birefringent material.

The photochemical method of image recording of carbazole - containing polymeric layers attributes to well-known methods of image recording. The CAMC copolymer with OMA photoplastic carriers has been investigated in details on the purpose to enlarge the image photographic characteristics of CAMC. The photopolymer layers were made by pouring from solutions. The structure of CAMC is 1:1 and contains OMA varying from 0 to 50mol percent. There were additionally added about 5-16 percent iodinophorm CHI₃ for photo-cross-linking of given copolymer layers. The best result of macromolecular photo-cross-linking in UV-rays were obtained with 60-70 mol percent CAMC containing copolymers. It can be connected with good flexibility of polymeric macromolecules. Optimal concentration of iodinophorm was about 8-10 percent. It has been used a coherent laser beam with (lambda) equals 420 nm for holographic images recording. There were obtained holographic gratings with resolution 1500 mm^-1 and diffraction efficiency 23 percent. This material has photographic sensitivity 10³ m²/J that allows using the explored copolymers for elaboration of a new optic media for holographic images recording.

With the help of tunnel microscopy it was carried out the experimental research of the form and quantity of defects formed on the back surface of Cu, Ag and Au samples, at irradiating their frontal surface by laser pulses. The correlation between quantity of defects arising on a rear surface of metal and intensity of its luminescence was observed. The offered mechanism of generation of emission, and also capability of research of the emergence of mobile dislocations on a surface of metal with the help of mechanoluminescence are discussed.

We have investigated the correlation of photoluminescence (PL) properties with certain etching conditions and laser annealing of porous silicon (PS). We used the optical second-harmonic generation and photoluminescence methods for studies of IR laser annealing of porous silicon. We observed that IR illumination by series of laser pulses causes decreasing of SH signal and increasing of luminescence efficiency for PS samples.

We report the studies of process of laser annealing of island Ge films on the SI substrates. Based on the time- resolved reflectivity measurements, we obtained the data concerning melting, the dissolution and the resolidification of Ge thin films on the SI after laser annealing with nanosecond laser pulse We observed periodic melting of the interface Ge-Si under an illumination by series of laser pulses that connected with the peculiarity of the solution Ge in Si.

We study the periodic damage structures that can be produced don the rough-surface of semiconductor when they are irradiated with a single beam of intense laser radiation. We observed a formation of periodic surface structures for porous Si with microscopic surface roughens. In the case of more strong rough Ge we observed an opposite effect to ripple formation: i.e. an effective destruction of resonance Fourier components of the random disturbed surface.

The time-resolved evolution of the cloud of the porous silicon (PS) particles produced by laser ablation is studied in situ by the analysis of the kinetics of photoluminescence (PL) signal. The cloud of the nanometer-sized silicon crystallites had the high enchantment of luminescence quantum efficiency (QE) in the red region of spectra. The slow PL kinetics component, which is due to the localized carriers, decays on a millisecond time scale. We observed high intensity of laser ablation process for light excited PS. We also study the emission of photons from remnants of porous silicon after laser ablation of PS sample. The red light generation was observed in this case of excitation of PS. Time-resolved experiments on the luminescence show that likely there are large lifetime phonons in quantum silicon wires.

We studied the process of formation of 3D polymer structures by initiating polymerization with laser radiation. Polymers based on such monomers as methyl methacrylate and ethyleneglycolmonomethacrylate were investigated. Polymerization was initiated by the fourth harmonic radiation of a Q-switched Nd:YAP laser without any specially introduced initiator. Initiation is provided by the direct photolysis of monomers. At this wavelength the absorption of monomers is significantly higher than the absorption of corresponding polymer. It results in bleaching of the media during polymerization.

Action of the resonance radiation of varied power on polymethine dyes coated as submono- and thicker layers onto glass and quartz was studied. Effect of the dye structure on the optical properties of molecular layers was explored. The layer absorption spectra within 320-1000 nm were measured for dicarbocyanine dyes differing in chemical structures and electronic symmetries. The absorption spectra of dye layers contain a few maxima, whose relative intensity is a function of the dye concentration on a surface, and are considerably broader than the solution spectra, irrespective of molecular symmetry. Irreversible transformation of the dye absorption spectra was studied under the action of resonance laser radiation of varied power and on heating in the dark. The heating and the pulsed laser irradiation of low power and energy lead mainly to the optical density redistribution among different spectral maxima. At high-power irradiation, the optical density redistribution is accompanied by the considerable decrease in the optical density. Simultaneously, the extinction coefficient of the layer increased in the short-wave edge of the absorption spectrum, i.e., outside the dye absorption band, indicative of dye destruction via irreversible photo oxidation. It is concluded that the dye layer contains a few types of absorption centers: two types of monomers, dimers, and probably, J-aggragates. The interaction with a substrate affects the symmetry of electronic density distribution in a dye molecule, whereas the irradiation and heating of a layer result in the destruction of dye and affect the relative amount of various absorption centers.

We report the results of experimental study of IR radiation detection in a bulk of compensated germanium. Au or Ni with deep levels in the forbidden energy ap was used as compensating impurities. In spite of great difference in their activation energies the change of electrical resistance of the samples under CO₂ laser illumination indicated the similar rise of carrier density in the valence band which can not be explained only by means of direct hole activation character of the electrical conductivity of compensated semiconductors. Evaluation of spatial quantity of in-homogenates in compensated semiconductors confirmed the importance of energetic bands bending due to the existence of ionized impurities complexes for IR detection.

The modification of C₆₀-film structure under laser and x-ray irradiation has been investigated. The wide spectral and dose ranges of irradiation have been applied: from visible light to hard x-ray and from low to high intensity, when the optical nonlinear effects appear. The structure changes manifesting close to nonlinear threshold have been found. They have exhibited the nonreversible effect contribution to the nonlinear parameters of initial C₆₀- films. The dependence of C₆₀-film structure modification on irradiation wavelength has been demonstrated by the photoluminescence and transmission spectral measurements, the solubility controlling, and data of x-ray diffractometry as well. The contribution of x-ray and a secondary electron flow to polymerization of the C₆₀-film has bene determined. The information about C₆₀- film modification may be used for optical limiting devices and for the development of UV and x-ray resists.

An optical limiting of the laser radiation over IR range in organic compounds based on polyimide has been studied. The non-linear transmission at a wavelength of 1315 nm as well as spectral properties of the compounds have been investigated. The result obtained have been explained by the donor-acceptor interaction mechanism that affects nonlinear- optical properties of organic molecules. The fullerene-doped polyimide structures have been determined to be effective optical limiting materials for attenuating a power density of more than 2 J cm² in the IR range.

The non-linear transmission of the laser radiation in the fullerene-containing NPP films has been investigated. Optical limiting of the laser radiation has been observed in the UV and visible spectral regions. The results obtained have been explained by reverse saturable absorption, two- photon and carrier-free absorption, and charge transfer complex formation.

We discuss different manifestations of the laser-induced homogenization (LIH) in the light-diffusing media - an abrupt decrease of the light diffusion in condensed media under the intensive light action. The key mechanisms of the LIH are discussed including the avalanche-like ones. We present the results of the simplest model, describing the LIH arising upon melting of a solid, when the abrupt drop of the light scattering occurs due to homogenization of optical properties of the medium.

The dry laser cleaning arises due to thermal expansion of the substrate and/or particle, when the corresponding acceleration force produces work sufficient to overcome the adhesion energy. The previous examinations of the dry cleaning were done for two mechanisms: 1) expansion of absorbing particle on the transparent substrate and 2) expansion of the absorbing substrate with non-absorbing particle. Nevertheless using model with conventional mechanism based on the 1D surface expansion, one can find threshold fluence by the order of magnitude higher than experimental one. In the present paper, we discuss the new mechanism for situation when the particle is heated due to thermal contact with substrate, and additional thermo deformation effect, caused by optical enhancement. It is shown that these effects can be responsible for relatively small threshold fluence for laser cleaning of SiO₂ particles from the surface of Si by ns-excimer laser pulse.

Under the impact of powerful laser radiation in semiconductors occur processes, essentially change their properties. For instance, in (1) observed annealing of ion- implanted silicon, vastly improving quality of semiconductor devices, made form it. In (2) was observed laser-stimulated diffusion of impurity atoms on the direction to surface, and in (3) on the contrary, deep into the semiconductor. In (4) an increase of velocity of chemical reactions on semiconductor surface under the influence of laser radiation was observed. In the present work spectra of radiation reflection of low power continuous CO₂-laser from the surface of monocrystals of semiconductor A_II B_VI compounds previously irradiated by powerful pulses of CO₂ laser were investigated.

A simple technique for density determination of nm-sized light-emitting areas on a flat surface such as those produced by quantum dots is proposed. The method is based on the measurements of luminescence intensity fluctuations at the center of inhomogeneously broadened spectral band from a sample illuminated through a series of mask with apertures in the 0.1-1 micrometers range. The fluctuation amplitudes depend crucially on the number of emitters involved. As shown by simulation the latter may be established with better than 100 percent accuracy as well as the averaged surface density. With aperture diameter as small as approximately 0,2 (lambda) in-depth discrimination of QDs in the aperture near-field is possible.

The interaction of subpicosecond laser pulses with metals is studied theoretically using phenomenological two-temperature model. A semi-analytical approach to a quantitative analysis of electron and lattice temperatures is presented. Using the nonstationary averaging technique the coupled system of nonlinear heat equations for electron and lattice temperatures is transformed into the set of four ordinary differential equations. Resulting system is convenient for the fast analysis of nonstationary laser heating and laser ablation with ultrashort laser pulses.

Crater shapes and plasma plume expansion in the interaction of femtosecond, picosecond and nanosecond laser pulses with various pure metal in air and noble gases at atmospheric pressure were studied. The craters formed at the surfaces were measured by an optical microscope profilometer with 0.01 micrometers depth and 0.5 micrometers lateral resolutions. The measurements of laser plasma expansion were carried out with ICCD camera with 3 micrometers spatial and 1 ns temporal resolutions. These measurements were made in 0-100 ns time delay range and at different wavelengths in 200-850 nm optical spectral range. Laser ablation efficiencies, crater profiles, plasma plume shapes at different time delays, rates of plasma expansion in both longitudinal and transversal directions to the laser beam were obtained. Experimental results were analyzed from the point of view of different theoretical models of laser beam interaction with plasma and metals. The laser pulse duration range used in our study was of particular interest, as it includes the characteristic time of electron-phonon relaxation in solids, that is, of the order off one picosecond. Thus, we could study the different regimes of laser ablation without and with laser beam/plasma plume interaction. It was found that for nanosecond pluses the laser beam absorption, as well as its scattering and reflection in plasma, were the limiting factors for efficient laser ablation and precise material processing with sharply focused laser beams.

An experimental and numerical study was conducted on ablation form ns-laser heated aluminum. The goal of present study is to clarify the laser ablation phenomena. In experiments, a YAG laser of 650mJ in 4-7nsec was used to perpendicularly illuminate an aluminum target. Time-resolved measurements were conducted using high-speed camera system. Also, a numerical simulation was conducted using CIP method. The experimental results of time-resolved measurements indicate that the target surface itself is melting until late after the laser irradiation. The SEM pictures of the irradiated indicate that the target surface itself is melting until late after the laser irradiation. The SEM pictures of the irradiated target surface are showing the generation of many minute protrusions. These protrusions near the part that laser is irradiated are facing toward the laser beam path and those of the surroundings are facing toward circumference. It is found by numerical simulation that this is due to the appearance of the critical point just after the laser irradiation. Since the laser beam goes around the critical point, the damaged part expands toward circumference.

Applications of ablation plasma to materials science have been carried out using pulsed laser ablation and pulsed ion beam evaporation. Although basic idea is similar each other, the energy absorption mechanism of the two processes differs a lot, yielding big difference such as in the preparation of thin films. Compared with the pulsed laser ablation, the pulsed ion beam ablation has an advantage of higher plasma density inherent to huge energy density on targets. Two examples will be shown for the preparation of hard films, for example films by pulsed laser ablation and B₄C films by pulsed ion beam evaporation.

The laser ablation threshold experiments were performed on pure metals with the fs Gaussian laser beam focused to 41.5 mm spot diameter onto metal surfaces. Three different ablation thresholds were distinguished. The multi-shot ablation threshold for Cu with 70 fs pulse was found to be 0.018 J/cm² and of one order to magnitude lower than that one observed previously. In the fluence range of 0.018- 0.2 J/cm² the ablation rate was approximately equal to 0.01 nm/pulse. The threshold dependence on the pulse duration was demonstrated in the range of 70 fs-5 ps for Cu. As the laser pulse width increased, the ablation threshold had the tendency to be higher. The ablation rate dependence on laser fluence for the other metals under study in our experiments with 70 fs was similar to that of CU.

Ultrafast time resolved microscopy of femtosecond laser irradiated surfaces reveals a universal feature of the ablating surface on nanosecond time scale. All investigated materials show rings in the ablation zone, which were identified as an interference pattern. Optically sharp surface occur during expansion of the heated material as a result of anomalous hydrodynamic expansion effects. Experimentally, the rings are observed within a certain fluence range which strongly depends on material parameters. The lower limit of this fluence range is the ablation threshold. We predict a fluence ratio between the upper and the lower fluence limit approximately equal to the ratio of critical temperature to boiling temperature at normal pressure. This estimate is experimentally confirmed on different materials.

The main feature of polymeric material sis the hierarcy of bonds between molecular groups. There are 'strong' covalent bonds connecting neighbor molecular groups of the same chain, and 'weak' molecular bonds between neighbor groups that belong to different polymer chains. The existing theories of laser ablation of polymers either do not take into consideration this feature or do not take into account the movement of the interface between condensed and gaseous phase. An important step in this direction has been taken in where the so-called bulk or volume model of laser ablation of polymers has been developed. In this model ablation of organic polymers is described on the basis of photothermal bond breaking within the bulk material, Here a first order chemical reaction is assumed, which can be described by Arrhenius law. Ablation starts when the density of broken bonds at the surface reaches a certain critical value. The position of the interface thereafter is fixed with this critical number. It has been shown, in particular, that the movement of the interface between the condensed and gaseous phases during laser ablation is of great importance. In the present paper we develop this model changing the Stefan-like boundary condition at the ablation interface with the physical Frenkel-Wilson condition, which is more appropriate physically and, on the other hand, more convenient for numerical calculations. According to this model, activation energy for elimination of a short enough polymer chain form the surface is proportional to the sum of the energies of weak bonds connecting this chain with the surface. We compare predictions of this model with the previously derived Stefan-like bulk model and with the predictions of surface photothermal model with respect to kinetics and dynamics of single-pulse laser ablation by nanosecond pulse. The parameters used in numerical calculation correspond to the KrF excimer laser ablation of polyimide.

We report first IR free-electron laser experiments to compare and elucidate the effects of surface-localized vibrational excitation versus bulk vibrational excitation on the ablation of polycrystalline diamond. The measured ablation yield values as a function of laser intensity indicate the existence of two separate thresholds. The lower intensity thresholds is identified as the ablation threshold, and the higher intensity threshold is associated with the formation of a plasma plume. The wavelength dependences of both thresholds indicate that eh C-H absorption occurring at surfaces and grain boundaries does not play a significant role in the ablation process. However, both thresholds are lower when the laser is resonant with the two-phonon bulk absorption band. These findings are consistent with the model that a rapid laser- induced phase transition to graphite is responsible for the low-intensity ablation of diamond at and above the first threshold.

Qualitative analysis of the gas-dynamical phenomena by the laser ablation of graphite under conditions of single-wall carbon nanotubes (SWNTs) suggests to reconsider the currently assumed mechanisms of SWNT formation in this technique and to conclude that it is a form of solid-liquid- solid catalytic graphitization of amorphous carbon or other imperfect carbon forms. The prosed mechanism of melting of catalyst particles followed by precipitation of SWNTs allows to explain the observed dependencies of the SWNT yield on the synthesis temperature and pressure. Critical inspection of the literature data shows that it might also play a role in other physical and chemical deposition techniques of SWNT synthesis.

In the present communication we consider theoretically the effect of a single UV USLP and two successive UV USLPs on absorbing dielectrics near ablation threshold within the framework of a surface evaporation model and bulk photothermal models, which apply to polymer-like materials. In the case of pair-pulse ablation we investigate the dependence of the ablated depth on the delay time between USLPs. We show that this curve is formed in two possible regimes. It is shown that these regimes influence the shape of the delay curve. We argue that these regimes are the same for the bulk model as well. It means that it is difficult to distinguish between the models investigating only this curve. We consider possible pump-probe experiment where USLP with the fluence somewhat higher than the ablation threshold is employed as a pump, whereas probe radiation allows to determine the delay time between pump pulse and the state of ablation. We show that combining the experimental data on determination of delay curve in pair-pulse experiment and the above pump-probe single ablation allows determination of an appropriate model. The result of theoretical modeling are compared with the existing data on time-resolved UV USLP laser ablation experiments.

The process of laser ablation of the thin film in solid or liquid phase in the before-evaporation regime is considered. The physical model of film ablation caused by thermal tension, occurring in the film by its fast laser heating, is proposed. The dependence of velocity of film fragment movement of the substrate surface on laser intensity is defined. The prosed conception of laser film ablation is used to explain the phenomenon of film degradation. The obtained results are in a good agreement with known experimental data.

The results of a complex study of the ablation of metals when they are acted on by radiation pulses 40-300 ns wide from neodymium laser are presented. Low-thresholds surface ablation has been detected in a number of metals at surface temperatures below the boiling point, before the instant plasma formation, with a burst of particles of the condensed disperse phase and the formation of microstructures with a characteristics size of 1-10 micrometers . A description is given of the laser-induced ablation model, based on the purely thermal action of laser radiation and the natural inhomogeneity of solids.

There are considered two effects of nonlinear light propagation that can play an important role in initiating of laser-induced damage of transparent materials: self-induced variations of light polarization of focused laser beam and developing of field instability in non-absorbing micro inclusions. The effect of self-induced variations of light polarization is considered qualitatively for focused laser beam with arbitrary focal spot. Detailed numerical study of the effect is fulfilled for Gaussian beams of low order. It is shown that any initial light polarization turns into elliptic one with inhomogeneous distribution of polarization-ellips parameters. Developing of field instability in transparent micro inclusions is other considered nonlinear effect. It is shown that transparent micro inclusion can initiate local field increase accompanied by positive feedback resulting in further field increasing near the inclusion. If the electric field strength exceeds damage threshold during nonlinear evolution in the inclusion then developing of field instability result in damage of micro-inclusion before electric field reaches certain upper level determined by ionization processes.

We study the temporal evolution of the distribution functions of free electron gas in metals and insulators for the case of irradiation with a laser pulse of moderate intensity. A microscopical description on the basis of time- dependent Boltzmann equations is used. The results show the sequence of excitation and relaxation of the electron gas leading eventually to thermal equilibrium. Due to photon absorption the occupation number of electron gas differs significantly from Fermi distribution. For high enough intensities about damage threshold, the energy exchange between electrons and phonos can be described with the two- temperature model. For low excitations we find a delayed energy transfer from laser-excited electron gas to lattice as compared to the two-temperature model. We obtain fluence- dependent thermalization times of the electron gas. For dielectrics we find that the essential process of free- electron generation is strong-electric-field ionization; no avalanche develops in femtosecond time reign. We propose an extended system of two rate equation taking the effect of energy dependence of impact ionization into account. This averaging approach can reproduce the evolution of free electron density in SiO₂ with reasonable accuracy.

There is considered formation of shock electromagnetic waves (SHEW) of visible spectral range as possible nonlinear optical phenomenon taking place at laser intensity close to damage threshold induced by femtosecond laser pluses in transparent solids. Main regularities of SHEW formation are studied on the basis of 1D model of plane-wave propagation in isotropic dielectric with nonlinear optical responses and dispersion. Special attention is pad to influence of color dispersion on SHEW formation and propagation. Necessary conditions for appearing of SHEW are obtained, in particular, threshold amplitude is estimated. There is presented a model for numerical study of SHEW formation and propagation influenced by dispersion of linear and nonlinear parts of effective refractive index. Using the simulation, we studied dynamics of SHEW formation on several optical cycles near leading edge of femtosecond laser pulse propagating in transparent medium. Important observed features of SHEW are discussed.

A new wave equation for the electrical field evolution of intensive femtosecond light pulses in isotropic transparent media is presented. It is demonstrated that a 'light bubble' can evolve from a few-optical cycle pulse propagating through a fused silica bulk. The two-octave spectrum supercontinuum is theoretically observed.

Localized surface plasmon-polaritons in small metal particles play an important role in a number o laser-induced surface processes. The intensity and the width of the corresponding resonances are determined by the dephasing time of the plasmon. To get information on the dephasing times, the linear spectroscopy methods are of limited use because of their inability to discriminate between the homogeneous and inhomogeneous line broadening. Consequently, the linear extinction spectra provide only the lower limit of the surface plasmon dephasing time. Nonlinear techniques, such as autocorrelation measurements of second and third harmonic generation employing bandwidth-limited femtosecond pluses and performed with an interferometric accuracy, were intended to give a direct access to the dephasing time of the plasmon excitation. In this contribution, we present the result of the theoretical modeling of the second and third harmonic autocorrelation functions and how that these particular nonlinear techniques suffer from the inhomogeneous broadening to almost the same extent as the linear extinction measurements. Moreover, the general relations between the liner absorption spectrum and second and third harmonic autocorrelation functions produced by an arbitrary inhomogeneous distribution of resonance frequencies are found, provided the resonance itself may be modeled as a slightly anharmonic classical oscillator. Finally, we propose one particular combination of linear and nonlinear results that may help to discriminate between homogeneous and inhomogeneous contributions to the line shape, and analyze the assumptions that lead to the unambiguous determination of the surface plasmon dephasing time.

Investigations on harmonic generation in laser-matter interaction of Nd:glass laser radiation with solid surfaces have been performed. Detailed measurements were made on the intensity of second, third and fourth harmonics, their polarization properties and spectral distribution, as well as dependencies of these characteristics on intensity and polarization of the incident laser radiation. Intensity dependence of second, third and fourth harmonics for p- polarized laser pump shoed a power law scaling of 1.5, 1.8 and 3.8 respectively. Maximal conversion efficiencies for second, third and fourth harmonic generation were observed in the range of 10^-8 to 10^-12. For p- polarized laser radiation, the generation efficiency was more than ten and hundred times higher in comparison to that for the s-polarized radiation for second and third harmonics respectively. Among other features, rotation of second harmonic polarization as a function of laser intensity showed a quite different behavior for p- and s-polarized laser radiation, and the second harmonic observed in the specular reflection direction was red-shifted for laser intensity exceeding 5 by 10¹⁴ W cm^-2.

There are considered non-thermal processes of femtosecond laser-induced damage of wide band-gap transparent materials. Dominating of thermal or non-thermal effects depends on radiation and material parameters among which pulse repetition rate, focal spot size and absorption play key role. Non-thermal mechanisms of damage and ablation can dominate at initiating stage and at low repetition rates. They are attributed to nonlinear electrodynamical processes such as higher harmonic generation of formation of shock electromagnetic waves. Considering interaction of shock electromagnetic wave with a particle in potential well, we derive expression for threshold of laser-induced ionization and delocalization. Thermal mechanisms can dominate at later stages of damage and ablation at repetition rates above 10 kHz. There are also discussed after-heating and non- equilibrium non-thermal processes taking place between initiating and thermal stages. There are considered several mechanisms of laser-induced ionization - multiphoton, tunneling, avalanche ionization, also ionization by higher harmonics and by shock-wave front. Estimations of ionization rates show that the latter two mechanisms can dominate at initiating stage of femtosecond damage and determine critically following ionization processes. Obtained results are compared with experimental data.

Investigations of nonlinear optical parameters of AU, Ag, Pt and Cu colloidal solutions by Z-scan method are presented. Nonlinear refractive indices of these solutions on the wavelength of Nd:YAG laser radiation and its second harmonic have been measured. Two-photon absorption and nonlinear susceptibilities of these solutions have been studied.