Removal of material from the surface of metals and semiconductors following irradiation with pico- or femtosecond laser pulses is a thermal process involving states of matter having unusually thermodynamic, hydrodynamic and optical properties.

An intense VUV-IR coherent light source based on the both spatial and temporal phase modulation in rare gas media induced by tera-watt laser field is presented. A spectra intensity of 1 GW/nm has been obtained from the UV to IR regions. An up-conversion broadband optical parametric amplifier based on the four-wave-mixing in a non- birefringence nonlinear materials has also been demonstrated for time gated spectra measurements with the ultra-broadband light source.

The exact steady-state solution of the optical Bloch equations for the density matrix of atoms interacting with a monochromatic field is found in a compact analytical form for closed F_g equals F yields F_e equals F + 1 transitions. The obtained solution is valid for arbitrary light ellipticity and intensity. Some applications of this new result are outlined.

An experimental and theoretically study is performed of the angular photoelectron distribution for three-photon ionization of Ba atoms through the 2(omega) -excited intermediate state 6p² (¹S_o) and the auto- ionized state 6p8s(³P₁). Rotation of the polarization plane of dye-laser radiation allowed us to investigate the photoelectron angular distribution. Electrons were counted with the help of a time-of-flight electron spectrometer. Employing the density-matrix formalism, expressions have been obtained for angular dependence of the differential ionizations probability. Possible experiments are discussed.

In a simple `free-electron' model framework, we develop an analytical approach to multiphoton processes in aromatic molecules using the Green's function technique. As an example, we calculate the electron polarizability of benzene ring. The results for benzene accord with the experimental values for static polarizability. Dynamic polarizability taken from theoretical investigation has poor agreement with the experimental data.

The Schwarz-Hora effect, observed under attempts to modulate an electron beam by laser light, was discussed extensively in the literature in the early 1970s. The analysis of the literature shows there are the unresolved up to now contradictions between the theory and the Schwarz experiments. The new model for the interpretation of the Schwarz-Hora effect is proposed. The problem of the description of the long-wavelength spatial beating in the Schwarz-Hora radiation is essential for the model and is considered in detail.

Laser plasma generated on the surface of solid targets located in gas atmosphere leads to the formation of a strong shock wave, which changes thermodynamic and spectral plasma characteristics accompanied by Stark effect. The registration of Stark shift and broadening of emission spectral lines allowed us to determine electron temperature and electron density for the ambient gas pressure range of 200 - 1200 Torr without considering presence of local thermodynamic equilibrium in the studied volume of aluminum plasma. The electron temperature and density of plasma increased along with gas pressure, which was explained by the formation of the more intensive shock wave. The velocity of laser plasma expansion in vacuum was obtained by measuring Doppler shift of weakly broadened lines of emission spectra, collected at two different angles from the normal of target surface. The measurement of line broadening, caused by square Stark effect, gave us an estimate of electric field in aluminum plasma. For Q- switched Nd:YAG laser operating at a 1.064-micrometers wavelength with a pulse energy of 0.6 J and a time duration of the laser pulse of 20 ns, the electric field in the studied plasma volume was 18 kV/cm for ambient gas (helium) pressure of 760 Torr.

Present report gives the results of experimental and numerical investigations of magnetic fields produced by crossed gradients of electron density and temperature in laser plasma. Plasma was formed in vacuum at radiation of HF-laser on a dielectric target. The nature of generation of magnetic fields on the other side of the target and outside of laser plasma flame was considered. Comparison of numerical results and results of experimental investigations was discussed.

Using the quasienergy set of wave functions: the equation for one-particle density matrix (kinetic equation) describing electron gas kinetics in high-power laser field with consideration for electron-electron and electron- lattice collision processes was derived. The solutions of this equation have been found for two limiting cases: (1) when the electron-electron collision frequency greatly surpasses the frequency of electron-lattice collisions and (2) in the opposite case.

The physics of the long-lived photon echo and the physical principles of the functioning of the optical phase memory, based on this phenomenon, are considered. The principal schemes of the optical echo-processors are discussed. The modern state of the elaboration of these processors is analyzed.

Population and third order nonlinear polarization coherent changes on Raman electronic transition of thallium atoms excited by a couple of 30 ps pulses of dye- and Nd:YAG lasers were observed. Collimated exciting and probing beams propagated through a heated cell of one centimeter length with thallium vapor. Population and nonlinear polarization dependences as functions of exciting pulses energy product were monitored using permanently delayed probing pulses.

Revivals of optical coherence of molecular photoassociation driven by two ultrashort laser pulses are addressed in the Condon approach. Based on textbook examples and numerical simulation of excimer molecules, a prediction is made about an existence of photon echo on free-bound transitions. Delayed rise and fall of nonlinear polarization in the half- collisions are to be resulted from resonant quantum states interference whether it be in gas, liquid and solid phases.

It is studied the effect of the ballistic phonons of heat pulses of the nanosecond duration on the inverted photon echoes in ruby and in LaF₃:Pr³⁺ for 4777 angstroms (³P_o - ³H₄) transition at temperature 2 K. The phonon pulses are generated by fast joule heating of thin Cu-film. The photon echo is used as the phonon detector. The decrease in the echo intensity is observed experimentally when ballistic longitudinal phonon pulse was propagated in optically excited volume during photon echo formation. The echo intensity is restored up to initial values by the second ballistic longitudinal phonon pulse in our experiment. In this case the each impurity ion is interacted with two alike phonon pulses after the recording and, accordingly, reading laser pulses. This indicates, that the main effect of the heat ballistic phonon on impurity consists in a shift of the impurity optical frequencies, instead of in relaxation transitions. The energy level shifts are not depended on duration of a pulse in experiment. The effect of the two pulses of the heat ballistic phonons is not additive.

A theoretical investigation is reported of the coherent nonlinear response of excitons and biexcitons in a thin semiconductor film subjected to resonant laser radiation. It is shown that saturation of an exciton transition results in an abrupt qualitative change in the nature of film transition from the regime of total reflection of the incident pulse at low pump amplitudes to oscillatory reflection at high amplitudes. A new area theorem is derived for ultrashort pulses: it establishes a correspondence between the areas of the incident, transmitted and reflected pulses. Anomalous transmission and reflection is predicted for large values of the nonlinear parameter. The equations of the state, describing bistable behavior of the amplitudes of the fields of the transmitted and reflected radiation, are derived for quasi-cw operation.

The model of the solitary defect formation wave (DFW) and the model of the impact ionization wave (IIW) ignited and propagated in semiconductors and dielectrics under intensive laser generation of electron-hole pairs are developed in close analogy with combustion wave. The characteristics of the DFW: critical laser intensity of DFW ignition, the shape, velocity of propagation and point defect concentration created by DFW are determined analytically. Analogous characteristics are obtained for the IIW. Quantitative interpretation of experimental results on modification of crystalline silicon surface by a train of picosecond laser pulses is carried out on the base of results obtained.

Solitonic propagation of IR laser pulse-induced wave of reflection and conduction change is investigated experimentally and theoretically. The temperature dependence of the wave velocity in Ge and high temperature superconductive ceramics is shown to be semiquantitatively described by the theory of slow defect recombination wave.

Observations of new physical phenomena, a photoinduced amplification of subharmonic of light in glass and instability of preliminarily induced optical anisotropy by illumination of medium to coherent radiation, are produced. Connection between phenomena is adduced. Physical models of phenomena taking into account of coherent photovoltaic effect are offered.

The first observation of narrow low-frequency resonances of the dielectric complex function in 1-asparagine monohydrated crystals is represented. The nature of the resonances and the possibility of excitation of thickness-extensional and thickness-shear piezo-acoustic modes are discussed.

Incident radiation intensity influence on spectral dependences of Faraday rotation and circularly polarized light absorption in single crystals CdCr₂Se₄ near the fundamental absorption edge were investigated. Strong nonlinear Faraday effect and nonlinear absorption were observed. The magnitudes of the effects are nonmonotonic function of the radiation intensity. The maximum increase of the Faraday rotation is equal to 100% of the linear effect value. The effects are explained by influence of photoexcited charge carriers on an excitonic resonance through screening of the internal electric fields existing in single crystals CdCr₂Se₄ as well as screening of the electron-hole interaction.

In this article we consider the intensity distribution of the light scattering by anisotropic (nonordinary) polaritons in the wave number--wave vector coordinates. We propose formulae for polariton spectra numerical calculation which are adequate for any wave vector direction and for resonant and nonresonant frequency areas. The case of polariton branch splitting along the wave vector coordinate when this vector directs close to optical axis of orthorhombic crystal is discussed as an illustration of the method availability.

Conditions of excitation of surface plasma waves depend on dielectric permittivity of a transitive layer directly bordering with a metal film in which they are exciting. Using a Langmuir-Blodgett film consisting of photochrome molecules of bacteriorhodopsin as a transitive layer, it is offered family of devices allowing to operate light with the help of light. Namely, light modulator controlled by light without using of external electronic devices, deflector of light controlled by light and converter of light of one wavelength of light to another one.

We have determined the effective density of deep photorefractive centers and the effective electro-optic coefficient by measuring two-wave mixing gains in a Ce:Pb_0.5Ba_0.5Nb₂O₆ photorefractive crystal and compared with those of PBN. We have also investigated the light-induced absorption through pump-probe measurements at relatively low optical power densities. The density of shallow trap centers and their properties are studied from the buildup and decay of the light-induced absorption and its dependence on light intensity and temperature. Two- center model is applied to explain the experimental results.

A hot free-carrier absorption in nonparabolic conduction bands is rigorously modeled on the base of Bloch waves. Computations are performed for GaAs, InAs and InSb. Other more relaxed (non)parabolic models can deviate from this up to 100%.

Reported is the observation of nonlinear gyrotropy of the aggregated colloidal silver solution, caused by the spatial dispersion of nonlinear response. In experiments, we measured the angle of self-induced rotation of the polarization plane of the pulsed laser source at (lambda) equals 0.532 micrometers and (tau) equals 11 ns. The technique developed allowed to separate the spatial dispersion effect from the nonlinear rotation occurring due to local response of a medium. The latter was measured in the pump-probe configuration via inverse Faraday effect.

The exciton absorption and emission bands in the presence of Bose-Einstein condensation (BEC) of excitons, induced by the coherent laser radiation is considered. The laser radiation creates the coherent macroscopic polarization of the crystal, which is described as a virtual BEC of excitons. The energy spectrum of the elementary excitations as well as the probabilities of the quantum transitions depend essentially on the frequency detuning (Delta) ^-. The nonequilibrium occupation numbers of out-of-condensate excitons n^ex_q arising in the presence of virtual BEC influence on the forms of absorption and emission bands.

There is considered a model describing abrupt local increasing of electric-field amplitude in transparent dielectric due to light-induced resonances in nonabsorbing inclusion. It is based on idea of self-induced formation of unstable field structure in dielectric microinclusions due to nonlinear variations of refractive index. Obtained results show that small (its radius is about wavelength) transparent inclusion can cause large field amplification. Possibility for field instability to arise is estimated using model of scattering for high-power plane wave by dielectric sphere and cylinder which radius is about or less radiation wavelength. Field instability is shown to have threshold. Presented results of computer modeling of nonlinear evolution of high-power laser radiation in dielectric cylinder confirm the developed ideas.

Theory of the resonant hyper-Raman scattering (RHRS) of light by the longitudinal optical phonons in semiconductors is developed. It was shown that the forbidden scattering mechanisms can result in features of the RHRS intensity frequency dependence under resonant conditions.

It is well-known that small (micrometers -sized) particles can be accelerated by a powerful laser pulse to considerable velocities. The laser-induced particle motion destroys the temporal coherence of the scattered light. The effect of particle motion on the coherence of scattered radiation is enhanced in concentrated suspensions of particles where the light scattering is substantially multiple. Hence the temporal correlation function of multiple-scattered light appears to be sensitive to the laser-induced particle flows. This point is of fundamental importance because traditional optical methods of particle flow diagnostics fail in the multiple-scattering regime. We analyze the possibility of optical diagnostics of laser-induced particle flows in concentrated multiple-scattering suspensions. We show that scattered radiation of the accelerating laser beam could give information on the `light-to-particles' momentum transfer, and, consequently, on the characteristic velocities of the laser-accelerated particles.

The theory of Bragg acoustooptic interaction of multi- component optical radiation with a single acoustic wave is developed. The multi-component radiation is assumed to be a multi frequency beam with two possible polarizations of each component. It is shown that the deciding factor for such interaction is to establish the phase synchronism conditions between every component of the optical radiation and the acoustic wave. This diffraction can be realized in anisotropic media only. These ideas are experimentally confirmed by using a two-color optical radiation diffracted on a single acoustic wave propagating in TeO₂ mono crystal. Two diffraction regimes of six-component Ar-laser radiation are proposed and investigated. A total diffraction efficiency up to 90% is obtained.

In this paper, we survey our previous and recent results of magneto-induced effects in second harmonic generation (SHG) from magnetic nanostructures. The degree of such effects is governed by the fine structure parameter and subsequently small in low order susceptibilities, yet enhanced at higher orders. One mechanism responsible for the enhancement of magneto-induced contributions to the SHG intensity is related to optical interference in the far-field region of the second harmonic fields generated by nonmagnetic and magneto-induced nonlinear polarizations. An interference model is considered for resonant and nonresonant, centrosymmetric and noncentrosymmetric media and is used to interpret the magneto-induced SHG results of Co nanocrystals and Gd monolayers.

Size effects in optical second harmonic generation (SHG) from Si(001)-SiO₂ planar micro-cavity structures are studied for fundamental wavelengths from 700 nm to 850 nm. The observed dependence of SHG intensity on the thickness of oxide layer is explained, in part, by an optical Casimir nonlocality arising from interference of zero-point fluctuations in micro-cavity, which is distinguished from microscopic interface effects. Detailed theoretical analysis of the Casimir nonlocal contribution to the quadratic susceptibility using a diagrammatic technique is performed for visible and IR regions. The difference in the length scale of the Casimir contribution at 800 nm and 1064 nm fundamental wavelength is discussed.

The dispersion of cubic optical susceptibility of submicron films of cyanine dyes J-aggregates is measured by a z-scan technique. The values of Im(chi) ⁽³), Re(chi) ⁽³) near to J-peak were 10^-5 esu. It was found that Im(chi) ⁽³) has a negative sign but at a low-frequency side of J-peak the sign is reversed. The measured dependence of Re(chi) ⁽³) ((omega) ) has compared with the value calculated by Kramers-Kronig transformation. The dispersion dependence of Im(chi) ⁽³), Re(chi) ⁽³) is quite well described on a basis of four-level model for J- aggregates.

This paper presents the results of investigation into the process of silicon surface solid-phase destruction under YAG:Nd laser pulses. The glow was registrated that was due to emission of the heated particles from the sample surface, which can be caused by microexplosions and microcracking of the surface owing to great thermoelastic stresses in the interaction area.

The paper presents the results of the study on nonthermal glow from the surface of metals, which is initiated by thermal deformations resulting from laser pulse action. The glow was registered from back, relative to laser pulse action, side of the sample. Oscillations of glow intensity have been revealed which are interpreted by the certain order of dislocations rising onto the surface.

This paper proceeds from basic research on carrier dynamics to applications in high-speed laser devices. Different retardation mechanisms are studied experimentally and theoretically providing input for the design of high-speed laser devices. Optically detected carrier dynamics in III/V semiconductor quantum well (QW) heterostructures perpendicular to the interfaces is studied. Photoluminescence emissions originating from different semiconductor layers are recorded time-resolved to probe the carrier dynamics between these layers. High spatial and temporal resolution is obtained experimentally, partly even in the nm and sub-ps ranges, respectively. Retardation effects are separated and studied experimentally and theoretically by corresponding model calculations. A material comparison shows that GaInAsP is beneficial due to considerable advantages in technological implementation processes and AlGaInAs is superior from a physical point of view enabling higher modulation band-widths due to larger conduction band discontinuities. The equalization of the carrier densities in the individual wells is found to be mainly retarded by hole thermionic emission. Hole transport in the p-sided confinement layer and electron capture from the p-sided confinement layer is also found to be also a limiting factor. These results are used to optimized AlGaInAs/InP lasers with asymmetric confinement layers. The p-sided confinement layer is reduced on the costs of the n- sided confinement layer to obtain (1) a faster hole transport across the p-sided confinement layer and (2) to accelerate the capture of electrons from the p-sided confinement layers being uncaptured during the transfer across the QWs. In our experiments a modulation bandwidth of 26 GHz is obtained. Even higher values are found in corresponding theoretical model calculations demonstrating an interesting development potential.

The theory of amorphization under pulsed laser melting of surfaces of crystalline semiconductors, based on mechanism of point defect capture and formation of nanometer periodic defect-deformational structures, is developed. The critical defect concentration and critical solidification front velocity at exceeding of which amorphization occurs are determined. The hierarchy of structural transformations at surface after melt solidification observed with decrease of laser fluency is analytically described.

It is shown that a high concentration of laser-induced point defects (interstitials, vacancies), interacting with each other through deformation field, phase transition with formation of nanometer periodic Defect-Deformational- structure occurs, accompanied by appearance of modulation of the surface relief. The shape, period and amplitude of relief modulation are determined as functions of defect concentration. It is shown that the local field factor at metal surface undergoes resonance increase (10² times) under scanning of the temperature in vicinity of roughening transition point lying just below the melting point.

Photoluminescence and picosecond differential absorption spectra measurements of the CdSe quantum dots embedded in phosphate glass are reported. The dots are in the strong quantum confined regime (the mean particle radius, 2.9 nm). The photoluminescence spectra are observed to depend on excitation intensity: increasing of excitation leads to appearing of a new luminescence peak. The differential absorption spectra show bleaching accompanied by time- delayed induced absorption on the high energy side.

Silicon crystallites produced by low temperature plasma- enhanced chemical vapor deposition technique have been shown size-dependent photoluminescent and second harmonic generation responses. The crystalline volume fraction was estimated by using Raman spectra. The grain sizes of crystallites were measured by using x-ray diffraction. The structural chemical properties of poly-Si films were studied by means of Fourier-transform infrared spectroscopy and transmission spectrophotometry. The size- and shape- dependent second-harmonic generation of poly-Si films is, also, studied. The second-harmonic generation intensity for poly-Si deposited by using SiH₄/SiF₄/H₂ gas mixture as function of such deposition conditions as hydrogen flow rate, silicon tetrafluoride flow rate, deposition temperature was studied.

A theoretical investigation of one- and two-photon absorption of weak probe light, respectively, by exciton- polaritons and biexcitons in the presence of a strong laser pulse in a planar microcavity embedded quantum well is presented. The strong pulse pumps the lower branch polariton into the biexciton and both states undergo the optical Stark splitting, which manifests oneself in the above mentioned absorption spectra. Besides the usual polariton gap an additional forbidden region for the pump and probe frequencies appear. This is due to the fact that the most part of the lower polariton branch is below the cavity photon mode energy. For this reasons the optical Stark effect manifests himself better in the biexciton two-photon absorption spectrum, while the renormalized lower branch polariton is not completely revealed in the one-photon absorption.

Photoinduced processes on surfaces of nanoporous semiconductors, such as Si and GaAs, are experimentally investigated. It was shown the possibility of change and control of desorption states on porous surface and, consequently, luminescence properties under laser irradiation by IR and visible light.

Using the generalized method of integral equations we developed the technique for the macroscopic description of any multicomponent medium with allowance of a discreteness of a medium for the first time in molecular optics. Proceeding from the microscopic parameters of the medium we derive the dielectric response and the nonlinear susceptibilities of a two-component crystal.

We show that a promising way towards photonic crystals for the visible range is connected with the synthetic opals which consist of close-packed submicron silica spheres. By filling intersphere voids with different liquids and titanium oxide it is possible to enhance refraction index modulation and to optimize the topology of the structure. Impregnation of opal with absorbing material, such as Fe₂O₃, allows us to investigate the influence of absorption on the optical properties of the photonic crystals.

It is demonstrated that two-photon polymerization can be employed as a basis for a technology for the fabrication of 3D micro- and submicrostructures, including structures with a periodically alternating refractive index. The rate of polymerization, energy expenditure, and required radiation doses characteristic of two-photon polymerization are estimated. The possibility to apply two-photon polymerization in the bulk of a medium to fabricate 3D photonic crystals in the optical range is discussed.

Mesoscopic structures with characteristic size either of the order of an electron de Broglie wavelength in semiconductors (1 - 10 nm) or close to the optical photon wavelength (100 - 1000 nm) exhibit non-trivial properties due to modified electron or photon density of states. 3D spatial confinement of electrons in nanocrystals (quantum dots) results in size- dependent energies and probabilities of optical transitions. The photon density of states can be modified in structures with strong modulation of the refractive index in three dimensions (photonic crystals) and in microcavities. Because of the essentially different electron and photon wavelengths, electron and photon densities of states can be engineered separately within the same mesostructure. We report here on synthesis and properties of semiconductor quantum dots corresponding to the strong confinement limit embedded either in a photonic crystal exhibiting a pseudogap or in a planar microcavity. We show that the interplay of electron and photon confinement within the same structure opens a way towards novel light sources with controllable spontaneous emission. Spontaneous emission which is not an inherent property of quantum systems but a result of their interaction with electromagnetic vacuum can be either promoted or inhibited depending on the modification of the photon density of states in a given mesostructure.

Self-phase modulation and compression of short laser pulses in 1D photonic band-gap (PBG) structures are considered as particular cases of the general problem of the propagation of short light pulses in photonic crystals. The nonlinear finite-different time-domain technique are applied to simulate the propagation of ultrashort laser pulses in linear and nonlinear 1D PBG structures. It is demonstrated that photonic crystals with embedded optical nonlinearity provide an opportunity to efficiently compress laser pulses to a duration of several optical cycles on a submillimeter spatial scale, providing new opportunities for the miniaturization of femtosecond solid-state laser systems. Examples of PBG pulse compressors that can be fabricated by means of currently existing technologies are considered.

The establishment of new phenomenological correlation between microscopic chemical structure and macroscopic linear optical and second order nonlinear optical properties of binary and ternary oxide materials have been carried out. It is shown that the most efficient binary oxide crystals have arranged in the place of chemical bond lengths on rosette of two extended ellipses with focal axes crossing on the line of simple oxides. The same ternary crystals have positioned in the space of chemical bond lengths on surface of four ellipsoids, which have been formed by rotation of these ellipses around minor and focal axes. The ellipse equation is a key criterion for formation of high efficient acentric crystals and it is defined by dimensional ratio of cations to tetrahedral and octahedral hollows of anionic sublattice. The new binary nitrate and iodate crystals have been predicted and synthesized with using of this concept.

Recently new borate crystals, CsLiB₆O₁₀ (CLBO), YCa₄O(BO₃)₃ (YCOB) and Gd_xY_1-xCa₄O(BO₃)₃ (Gd_xY_1-xCOB) have been developed by the present author. Here, the growth and nonlinear optical properties of CLBO, YCOB and Gd_xY_1-xCOB crystals are reviewed and their properties are discussed in relation to those of other nonlinear optical crystals, such as (beta) -BaB₂O₄ and LiB₃O₅.

The results of the tests for the second harmonic generation in powders of halogenosubstituted nitrodiphenyls are presented. The 4,4'-iodine-nitrodiphenyl single crystals have been grown from a solution, their linear and nonlinear optical characteristics have been measured. The Miller's constant for this crystal is one of the largest among investigated as far as we know.

Spectroscopic characterization of chromium doped calcium tetragermanate single crystals had been investigated. The investigations showed that these crystals may be considered as promising material for an active medium of tunable solid- state laser of near IR-range.

Bi₁₂TiO₂₀ crystals doped with Nb atoms ranging 0.05 - 0.2 wt.% are grown from non-stoichiometric melts by modified Czochralski pulling technique. Doping studies showed that Nb⁵⁺-ions occupy tetrahedral sites in sillenite lattice. Experimental results on spectral dependent characteristics, such as, absorption, photochromic effect, photoconductivity and electrooptic efficiency are presented. Comparison with similar properties of Bi₁₂TiO₂₀ crystals doped with another pentavalent atoms (V,P) is discussed. A relationship of these characteristics with local structural defects in doped Bi₁₂TiO₂₀ lattice is proposed.

Optical and nonlinear optical properties of LiNaCO₃ single crystals in triclinic and hexagonal phases have been investigated. The refractive indexes were measured for triclinic phase by means of prism method. Sellmeier equations and constants were determined.

The influence of acidity of KDP salt solution on KDP crystal properties has been investigated. A number of crystals were grown from acid solutions in wide range of solution acidity. Optical properties of the crystals were studied. It has been found that UV absorption of KDP crystals depends on the acidity of solution.

The new nanolithography technique realized experimentally using the local field of femtosecond laser pulses enhanced in nanoscale region due to lighting rod effect and to the excitation of local resonances in STM tip--substrate system. Surface topography analysis in STM mode demonstrates the controlled surface modification in a suitable regime of intensity parameters and femtosecond laser pulses focusing in the STM tip region.