Laser-induced plasma-assisted ablation (LIPAA), in which a single conventional pulsed laser of small size is employed (typically 2^nd harmonic of Nd:YAG laser), enables to process transparent materials like glass with micron order spatial resolution, high speed and low cost. In this process, a laser beam is first directed to a glass substrate placed in vacuum or air. The laser beam passes through the substrate since the wavelength of laser beam must have no absorption by the substrate for the LIPAA process. The transmitted laser beam is absorbed by a solid target (typically metal) located behind the substrate. The target is then ablated, resulting in plasma generation. Due to the interaction of the laser beam and the laser-induced plasma, significant ablation takes place at the rear surface of substrate. This process demonstrates surface microstructuring, crack-free marking, color marking, painting and selective metallization of glass. Based on these achievements, we have developed a prototype of workstation of LIPAA microfabrication system which is now commercially available. The discussion includes mechanism and practical applications in industry of LIPAA process.

With the increasing use of ultrashort laser pulses and nanoscale-materials, one is regularly confronted to situations in which the properties of the media supporting propagation are not varying slowly with time (or space). Hence, the usual WKB-type approximations fail, and one has to resort to numerical treatments of the problems, with a considerable loss in our insight into the physics of laser-matter interaction. We will present a new approach which allows a fully analytical solution of such problems, based on a transformation of the propagation equations into a new space where phase accumulation is linear with either time or space, which greatly simplifies their treatment. Though this method is restricted to some special models of the time or space varying dielectric constant, those are however general enough to encompass practically all experimental situations. It allows to introduce the concept of “non-stationarity induced” (or “inhomogeneity induced”) dispersion. We will analyse the problem of reflection and propagation in two types of media whose dielectric constant vary rapidly at either the laser period or the laser wavelength scale. Extension of such techniques to the case of arbitrarily high non linearities will be considered too.

No Abstract Available.

UV light is one of primary factors associated with cataract formation in the eye lens. α-, β-, γ-Crystallins maintain lens transparency, and damage to these proteins plays a major role in cataract formation. The effect of XeCl laser radiation (308 nm) on β_L-crystallin solution is studied. The strong dependence of protein aggregation kinetics on both laser fluence (w) and repetition rate (F) is investigated. The kinetics features are similar to those of carbonic anhydrase photoaggregation studied previously.

An original compact test method of studying the influence of a modified Nd:YAG laser beam irradiation at λ = 1.32 μm on an IR-Ge window has been investigated: optical parameters, surface temperature, morphological deformation have been measured in real time and compared with theoretical simulations.

Pulsed irradiation from CO₂- and Nd:YAG lasers focused on the front side of different plates produces nearly instantaneous surface changes on the rear side of the plate. The responses of the materials depend on physical parameters such as pulse energy and duration, photon energy, the absorption and mechanical characteristics of the target material. The equipment built up for visualization of these phenomena consists of a cw. He-Ne laser, a digital CCD camera and a fast computer. The analysis is done using Digital Speckle Photography (DSP). Using focused and defocused laser speckle patterns, DSP enables measurement of in-plane strain fields, Brownian motion and residual micro-structural changes in the material caused by a laser pulse. Results are obtained at the frame rate of the digital camera and allow the creation of animated real-time or “movie” sequences. Results from CO₂- and Nd:YAG pulse interaction on Al₂O₃ ceramics and steel plates will be presented. The Brownian motion during the relaxation phase is more or less localized to the impacted area for both materials and both wavelengths but the relaxation times differ significantly. Steel also exhibits some residual material changes and doesn’t recover completely while Al₂O₃ returns to its initial state some time after the impact.

Interaction of laser radiation with solid targets - actively developing area of modern researches. But the processes occurring on the backside of a sample are little investigated. It is revealed with the help of tunnel microscopy methods, that on the surface of Cu, Au, Mo, Pd, W and of some other metals are formed defects looking like prismatic holes with strictly certain corners and linear sizes ~10 nm at any way of loading. It is investigated kinetics of the sizes growth, accumulation and destruction of the defects. It is found, that such defects as microcracks, porous and lines of sliding are formed at superposition of prismatic defects. Operation with a laser pulse has allowed: to choose the value of the energy entered into a sample, with the good accuracy to register the beginning and the end of input of energy, to locate a place of input, to calculate temperature and pressure increasing. Thickness of samples and energy of the laser pulse got out such: the tunnel microscope have to register changes of nanorelief on the backside in absence of a plasma fuel on irradiated - the frontal side of a sample. It has provided an opportunity to compare received nanorelief topograms of the back surface, to investigate cyclic regime and also to count up quantity of new appearing defects on topograms of a surface. It for the first time has allowed to establish interrelation between change of the nanorelief of the back surface, caused by the exit of dislocations on the surface and number of laser pulses irradiated on the frontal side. That essentially opens an opportunity of management and formation of the given roughness of a metal surface.

No Abstract Available.

The thermo-induced processes leading to the abrupt growth of the light transparency in the high-scattering media due to its homogenization under the intense laser beam action has been studied and discussed. It has been studied experimentally the light beam penetration into the solid dispersed stearin during its softening and melting under the laser-light action. The description and explanation of the experimental results has been done in the framework of the model based on the assumption, that the light scattering is defined by some phenomenological parameter namely the “order parameter” which is linked with the grain boundaries concentration in the non-homogeneous medium.

The spectral characteristics and the orientation of absorbing centers in the polymethine dye molecular layers on solid dielectric substrates were studied. Depending on thickness, the layers have from 1 to 4 molecular components, differing in the absorption spectra and title angles. The components of submonolayers always possess one type of angular distribution (the first type). In multilayers two types of the angular distribution of components was observed. The action of laser light does not affect the component orientation in layers characterized by the first type of angular distribution. In layers with the second type of angular distribution the reorientation of components was observed under the action of radiation. The relative yield of this process increases with increasing single-pulse energy density. It was suggested that the photostimulated reorientation of components results from an increase in the vibration energy, which is stored by absorbing component of the layer and transferred to its other components not absorbing the radiation.

Films of fluorides may crystallize during vacuum deposition on substrates that leads to undesirable diminishing of transparency of films (having optical thickness more than 3 ÷ 5 μm) for the visible spectral range. To solve this problem we carried out investigation of optical properties of alloyed BaF₂, CaF₂, and PbF₂ films and we demonstrated the possibility of deposition of films being transparent in visible and infrared ranges. We defined optimal values of concentration of alloying impurities and functional dependencies of impurity's concentration and optical losses. Based on alloyed BaF₂ films there were synthesized, made and researched interference coatings for lasers in visible and middle IR spectral ranges. The synthesis was realized due to special elaborated techniques allowing to get over the restriction of the number of film-forming materials with different refractive indexes and to produce coatings with required spectral characteristics. There were shown examples of the set of multilayer film coatings functioning successfully for laser radiation on wavelengths 0.63 and 10.6 μm simultaneously.

The comprehensive results are presented on the behaviour of high purity synthetic quartz glasses under the action of intensive ionizing radiation (x-rays and energetic electrons) and UV laser radiation with 248-nm wavelength. They are concerned to the application of e-beam-pumped large-size KrF-laser as a driver for the Inertial Fusion Energy.

From wave Maxwell equation we derive a system of differential equations described multiwave backward and forward stimulated Raman scattering with diffraction effects. The results of numerical simulations of this system are quantity and quality agreed with experimental results. The numerical simulations of quasi-phase matched forward and backward SRS showed that the influence of backward SRS on QPM structure realization results in the small difference between layers length of optimal QPM stmcture and small decreasing of resulting anti-Stokes conversion efficiency (~25%at backward and forward SRS, ~3O% at forward SRS). The oscillations of optimal layers length are partially connected with backward SRS influence and with insufficient precision of layers length determination due to high computational complexity of this task.

No Abstract Available.

Experiments on the Equation of State (EOS) of Carbon were performed at the PALS and LULI laboratories. We used Carbon samples with two different value of initial density, in order to explore a wider region of the phase diagram. We obtain experimental data for carbon Hugoniot at Megabar pressures induced by laser-driven shock waves. The target rear side emissivity due to the shock unloading was recorded from (two-materials two-steps) targets (Al-C) with space and time resolution. By applying the impedance mismatch method, a direct determination of relative EOS points was obtained. Experimental data are compared with previous experiments and with theoretical models. Our results indicate a higher compressibility of carbon at Megabar pressures compared to theoretical models.

No Abstract Available.

A Nd:YAG laser was employed to ignite methane- and hydrogen-air mixtures to investigate relevant parameters of laser ignition. The lean side ignition limit of methane was found to be at air/fuel-equivalence ratios (λ) of 2.4 applying a laser pulse energy of 50 mJ. It has to be mentioned, however, that above λ = 2.2 only slowest combustions causing weak pressure rises could be observed. Successful ignitions of hydrogen-air mixtures were achieved up to λ = 8 but it was not possible to examine the lean side limit due to weakest pressure rises far below detection limits for λ >8. Despite much lower values of minimum ignition energy for reported hydrogen-air mixtures in the literature, the minimum laser pulse energies examined for ignition are of the same magnitude as for ignition of rich methane-air mixtures lying around 5 mJ. Minimum pulse energy needed for ignition was decreasing with increasing pressure for hydrogen-air mixtures showing the same trend as in case of methane. The ignition delay time for hydrogen at λ = 2.0 could be observed as ~7 ms being 40 times shorter compared to methane at the same air/fuel ratio. Unfavorable transmission losses of laser energy were observed for methane/air mixtures below λ = 2.1 demanding optimized focusing optics and temporal pulse shaping for future laser ignition systems.

Laser ablation of porous silicon as a function of laser wavelength and width of silicon nanowires was studied in our experiments. The time-resolved evolution of the cloud of the porous silicon particles produced by laser ablation is studied in situ by the analysis of the kinetics of photoluminescence signal. The laser ablation of porous silicon produced by pulses of 532 nm or 337 nm radiation with addition of synchronized power pulses of 1064 nm radiation. The cloud of the nanometer-sized silicon crystallites had the high enhancement of luminescence quantum efficiency in the red region of spectra. The slow PL kinetics component, which is due to the localized carriers, decays on a millisecond time scale. The squeezed electron-hole plasma heating by IR-laser radiation may produce a damage of silicon nanowires. The fragments of nanowires in cloud must be smaller, than the critical length. The energy of excitation of e-h pair in fragment with contribution of longitude quantum modes must be lower than energy of the excited photons. Particles with lesser length don't absorb excited laser radiation and don't damage. For this case we may speak about the quantum mechanism of laser ablation of nanowires.

“Self-coordinated” method is used in this paper in order to solve approximately nonlinear problems in electrodynamics and in thermal physics. Comparison of results between the exact solution and the approximate solution, obtained by using “self-coordinated” method is shown. This approach is also used to estimate thresholds of electric-dynamic and thermal instabilities for condensed media with optical nonlinearity of different kind.

There is presented a physical interpretation of Keldysh's calculations of laser-induced ionization of solids. The aim of our considerations is to understand the generality of Keldysh's formula for ionization rate and to determine the area of its validity. In particular, we show the sensitivity of the ionization rate given by Keldysh's formula to the details of the band structure. In that connection we discuss the applications of Keldysh's formula to interpretation of experimental data on laser-induced ionization of solids.

This review is devoted to a long-term investigation into the nature of the laser-induced damage of silicate glasses. Besides damage threshold measurements, it includes data about linear and nonlinear absorption, multiple pulse damage, and subthreshold modification of media. The experiments were carried out over a wide range of wavelengths, pulse durations, and spot sizes. As an important result, we show that the threshold power density of the intrinsic damage of the boro-silicate glass at ~1 µm wavelength does not depend on pulse duration from 2x10^-13 to 3x10^-8s as long as self-focusing is avoided. This result cannot be explained by existing theories and indicates that the damage mechanism involves a collective response of a certain volume in the dielectric as a whole, rather than the accumulation of electrons via individual generation processes, like multiphoton, tunneling, or avalanche. Special attention in the research was paid to investigation into the processes of electron excitation in alkali- and lead-silicate glasses.

Periodical variations of the optical properties of solids are interesting for applications to optoelectronic materials. One path to the realisation of such structures could be the spatially dependent photoburning of optically active lattice defects. In this experiment, specially prepared radiation defects in A1₂0₃ are submitted to illumination by two orthogonally polarised copropagating femtosecond pulses (polarised along the ordinary and extraordinary directions). Due to their different light velocities, the two pulses overpass each other inside the material, and the local behavior of the resulting polarisation produces a spatially periodic excitation of the defects with a limited spatial extension. We measure the defect luminescence which exhibits this spatially localised periodical structure. We studied the influence of the pulse duration on the width of this periodical structure and found that it has no effect when the pulse duration is varied using the chirp induced by group velocity dispersion. On the contrary, if the pulse duration is changed by manipulating the spectrum of the radiation, one observes a linear dependence of the spatial width of the modulation with the pulse duration. Hence, it is not the pulse duration that matters, but the coherence time.

In this paper we report on the state-of-the-art of the ultrashort (fs) laser pulse-driven surface microprocessing of materials [metals, semiconductors and dielectrics (glasses and polymers)]. We emphasize the advantages of fs time scale pulses of laser-matter interactions, e.g., no heat effects in laser-coupled outside zones in plasma breakdown below intensity scales. A two-temperature model (energy coupling between electronic and phonon subsystems), the role of Dember effects, and ballistic transport are also considered.

There is proposed and described a physical model for possible sequence of effects induced by femtosecond high-intensity laser pulses in semiconductor and dielectric crystals. Basic points of the model are considered on the basis of the simplest estimations allowing to judge if the points do not contradict general physical regulations. Main advantage of the proposed model is capability of explaining extremely deep heating induced by super-short laser pulses and drilling of high-aspect holes.

Fresnel formula for the normal incidence of light is generalized to the case of reflection of broad-spectrum radiation off a dielectric with nonresonant dispersion and nonlinearity. Considering reflection of few-cycle light pulses off a bloomed dielectric interface, we show that self-division of a reflected pulse can occur at low incident intensities, while substantial modification of the pulse shape including self-compression is possible at higher intensities.

In present paper we enhance the model of polarization response in field of extremely short pulse by a pseudoclassical description of multiphoton ionization. The system of material equations now includes a part related to a ionization nonlinearity of the optical material. We also obtain a new wave equation, which describes extremely short pulse propagation in tnmsparent dielectric when electromagnetic field intensity values approach to a boundary of dielectric destruction beginning. The equation is used for modeling computations, numerical analysis of pulse propagation. Also new expressions for media refraction index are derived from the equation.

Quantum physical aspects of near-field optics are discussed on the basis of photon wave mechanics, and the upgraduation of the present transverse propagator formalism to the field-theoretic level described.

A simple model resembling those used in scanning tunneling microscopy is proposed for an optical probe tip. The tip is considered as a pointlike source (detector) displaced from the apex in the direction towards or from the sample. The exact position of this point depends on the shape of electric field lines within the gap and is a crucial factor determining the probe imaging properties. For various probes, both the aperture and apertureless ones, a general expression relating the lateral resolution with the corrugation amplitude, the gap width, and the tip (the aperture) radius is obtained.

The development of new principles for near-field probe design has been crucial for near-field technology progress for the last ten years. Employing surface polaritons gives the new opportunity for near-field probe development. Using this waves it can be provided not only efficient energy channel along near-field probe but good field localization in the tip.

A theoretical model of the interaction between finite mesoscopic objects within the layer structure situated on a substrate and the light in the near-field zone is presented. Consideration is based on a set of self-consistent integral equations for the electric field obtained from the Maxwell equations using a Green-function technique. In the work we give special attention to construct in the quasi-electrostatic approximation the dyadic Green's function of the reference system, which includes the substrate and the solid layer embedded in an infinite homogeneous medium. Our approach also allows us to construct the Green's function for two mediums with plane interface. We use unretarded approximation due to the fact that the distances between all points, which are included in the consideration, are assumed to be much smaller than the wavelength of the light in SNOM. On the base of this approach we obtain the analytical expression of the dyadic Green's function in direct space and numerically calculate the distribution of electric field intensity in the system. We consider two SNOM configurations. We show that the layer structure and substrate may play significant role in image formation. In the work we also discuss the scattering problem of longitudinal surface polaritons in SNOM of the collection configuration.

The theoretical study of the some processes taking place under the intense light excitation of the small area of the semiconductor surface by the short laser pulse had been carried out. The results of the performed analysis show that the absorption due to the “impurity depletion” must be taken into account in the processes of the ultra-short pulse action on the extremely small areas of semitransparent materials.

No Abstract Available.