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Publications (267)
Total ionization yields are reported for the noble gases in ultrastrong fields. The intensity range studied is from 1015W/cm2yy to 1018W/cm2 with ionization charge states from one to twelve. Sequential ionization processes are modeled by tunneling ionization and
shown to be accurate within a factor of two near saturation. Nonsequential, multielectr...
Irradiation of molecules by strong optical fields readily leads to rupture of one or more molecular bonds. Such rupture is
a consequence of field-induced multiple electron ejection from the molecule, leaving behind two or more ionic cores that experience
strong Coulombic repulsion. The resulting Coulomb explosion occurs on ultrafast time scales. It...
We present, in this chapter, numerical results of high order harmonic generation spectra (HOHG), in the Born-Oppenheimer approximation, of the diatomic molecular ion H+2 and the linear triatomic molecule H2+3 under strong laser fields. We revisit, first, the standard electron classical re-collision model. The atomic limit of 3.17 Up for re-collisio...
Polyatomic molecules undergo neutral dissociation in moderate intense laser fields. As a typical molecule species, methane
has been studied in the laser intensity of 1012 – 1013W/cm2 of a Ti-sapphire laser (λ = 800nm). The fragments of electronically excited CH (A 2Δ, B 2Σ, C 2Σ+) and H (n = 3), where n is the principal quantum number, are observed...
Recent progress in the generation of multiterawatt optical pulses into the 10-fs range is reviewed. A design, performance
and characterization of a compact titanium-doped sapphire laser system based on chirped-pulse amplification, which has produced
a peak power of 0.85-PW (850-TW) with 33-fs pulse duration is described. Further extension of the sy...
The nonperturbative analytical approximation method known as the SFA (Strong-Field Approximation) is traced to its roots in
the early days of strongfield physics. Although the SFA is now the primary analytical method used in practice, several departures
from the appropriate rules of application have arisen that needlessly restrict the broad power o...
We discuss the ionization and explosion dynamics of rare-gas clusters under intense femtosecond laser pulses. On one hand,
we show how a microscopic treatment by means of a mixed quantum/classical approach provides detailed and time-resolved insight
into the mechanisms of excitation and ionization of the irradiated clusters. Furthermore, we compare...
Powerful femtosecond laser pulses propagate in an apparent form of filamentation in all transparent optical media. This universal
nonlinear phenomenon is currently an interesting topic of research at the forefront of applied physics and attracts more and
more people to enter this field. This paper attempts to clarify some of the fundamental physics...
This second part of our review is devoted, in particular, to the description of the heating of a background material induced
by fast electron propagation, the propagation geometry of fast electron beams (including the issues of possible collimation
and filamentation instability), the formation of electron bunches, the refluxing of electrons in the...
We discuss the recent progress in the theoretical study on ionization processes of rare-gas atoms in strong optical fields,
in atomic physics and in nonlinear dynamics. Special emphasis is placed on using the notion of trajectories in the study,
which are particular Feynman paths in quantum mechanics. In terms of trajectories, both mechanisms of tu...
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We developed a technique for controlling the duration of XUV pulses by modulating the polarization of an intense short pulse We developed a technique for controlling the duration of XUV pulses by modulating the polarization of an intense short pulse
and using this pulse for high order harmonic generation. This approach allows c...
When ultrashort (fs), high-power laser pulses propagate through the atmosphere, extended plasma filaments form and emit white light in a spectral range spanning from the ultraviolet (230 nm) to the infrared (4.5 µm). This strongly non-linear optical phenomenon results from a dynamical balance between respectively focusing and defocusing Kerr- and p...
An effective scheme for the laser control of wavepacket dynamics applicable to systems with many degrees of freedom is discussed.
It is demonstrated that specially designed quadratically chirped pulses can be used to achieve fast and near-complete excitation
of the wavepacket without significantly distorting its shape. The parameters of the laser p...
The static electric field effects on nonlinear carrier dynamics in low-doped GaAs bulk under the influence of an intense sub-terahertz
field are studied by a three-dimensional multivalleys Monte Carlo simulation. The conversion efficiency is calculated by using
the appropriate Maxwell equation for the propagation of an electromagnetic wave along a...
By using the continuous wavelet transform with Haar basis the second-order properties of the wavelet coefficients are derived for the random telegraph signal (RTS) and for the /f noise which is obtained by summation of many RTSs. The correlation structure of the Haar wavelet coefficients for these processes is found. For the wavelet spectrum of the...
We discuss the role of strongly driven electrons in the generation of attosecond laser pulses and in time-resolved experiments
that can be performed using attosecond lasers. We show that the formation of attosecond laser pulses in high harmonic generation
is an inevitable consequency of the physics of atoms in strong laser fields, combining the sub...
We demonstrated accurate pulse shaping of amplified femtosecond laser pulses by modulating the amplitude and the phase prior
to regenerative chirped-pulse amplification. Based on a spectral interferometer, the pulse shaper was adjusted to compensate
for a transfer function of the amplifier consisting of the gain narrowing and self-phase modulation....
Ionization of organic molecules irradiated with intense infrared femtosecond pulses is explained from the perspective of intact
molecular ion formation. Although fragmentation is more suppressed in general by femtosecond pulse excitation than pico- and
nanosecond pulse excitations, molecules are still often heavily fragmented. Among the excitation...
Two laser-plasma processes among several others, namely the formation of relativistic electromagnetic solitons in warm plasmas
and the ion acceleration driven by the interaction of ultraintense and ultrafast laser pulses with thin solid targets, have
attracted great scientific interest in the last few years, both from a fundamental point of view an...
Rapid progress in recent years in the development of high power ultra-short pulse laser systems has opened up a whole new
vista of applications and computational challenges. New experimental developments in the field of extreme nonlinear optics
will require more rigorous electromagnetic propagation models beyond those existing in the current litera...
Fast electrons are generated in the interaction between intense ultra-short laser pulses and the target. This interaction
depends on the laser’s intensity, polarization, incident angle, the scale length of the plasma, and the target material. In
this review, recent studies carried out at our laboratory on the dependence of the fast electrons on the...
The focusability of intense coherent radiation generated by high-order harmonic conversion is investigated. A variety of focusing
mirrors are tested and used in the focusing experiments. We demonstrate the focusing of an extremeultraviolet/soft X-ray beam
to a 1 µm spot size with a peak intensity as high as 1 × 1014 W/cm2, which is sufficient to st...
High-order harmonic generation in a long gas jet is controlled in the space and time domains using chirped and self-guided
femtosecond laser pulses. Since high-order harmonic generation is intrinsically connected to the ionization process of harmonic
generation medium, ionization effects on high-order harmonic generation should be properly understo...
We show that different schemes can be now followed to produce collimated X-ray radiation using laser systems. By focusing
intense femtosecond laser light onto a gas jet, electrons of the plasma can be manipulated to generate ultrafast (femtosecond)
X-ray radiation in the forward direction along the laser axis. In this chapter we discuss nonlinear T...
The nuclear dynamics of polyatomic molecules in intense laser fields (∼1 PW/cm2) is studied through the momentum imaging of the fragment ions produced through Coulomb explosion. Characteristic nuclear
dynamics that occur on the multidimensional potential energy surfaces in intense laser fields, such as sequential and concerted
bond-breaking and hyd...
X-ray line emissions from ultrashort high-intensity laser-produced plasma were studied in order to clarify the physics of
energy transport associated with the generation of ultrashort X-ray pulses for use in various applications. This article reviews
two topics. The first is the application of Kα spectroscopy to the study of energy transport in las...
Calculations of the frequency noise spectra and of the coherence functions between the electrical and the optical noises for a single-mode packaged vertical surface emitting laser (VCSEL) are reported.A rate-equation model for an index guided VC-SEL is used, implemented with the electrical noise model including the intrinsic device, the package and...
This book series addresses a newly emerging interdisciplinary research field, Ultrafast Intense Laser Science, spanning atomic and molecular physics, molecular science, and optical science. Its progress is being stimulated by the recent development of ultrafast laser technologies. Highlights of this second volume include Coulomb explosion and fragm...
Generation of second and third harmonics of a pump wave, taking place during electron beam propagation in a plasma with a return current, is investigated. Polarization properties and generation efficiency are specifically addressed. Analytical dependencies of the investigated physical values are reported for both the cases when the generation mecha...
In this review, the physics of short-pulse laser-produced plasmas at moderate intensities is described, together with applications
to X-ray sources and material processing.
The self-compression phenomena of intense femtosecond pulses in normally dispersive solids were investigated experimentally.
Both un-chirped and negatively chirped laser pulses were used as input pulses. It is demonstrated that intense femtosecond
laser pulses can be compressed by the nonlinear propagation in the transparent solids, and the tempora...
Strong-field processes in the few-optical cycle regime are significantly affected by the carrier-envelope phase of the driving
pulses and the control of such parameter is essential for many application, particularly for the generation of isolated and
reproducible attosecond pulses. In this chapter we have reviewed, both from an experimental and a t...
A concise overview of new optical properties of dense nonequilibrium plasma formed on the solid state target boundary is given.
In this chapter, we describe phenomena such as the third harmonic generation in the skin layer, collisionless electron heating
in the high frequency skin-effect regime, absorption, and reflection and transmission of radiat...
A review of several correlation techniques used to extract quantitative information from two-dimensional images obtained with fast-frame CCD cameras is presented. Three examples are discussed that demonstrate the power of these techniques for revealing field-induced dynamics: (1) the relative probability for Coulomb explosions of CO
26+ as a functi...
We consider dynamical tunneling between two symmetry-related regular islands that are separated in phase space by a chaotic
sea. Such tunneling processes are dominantly governed by nonlinear resonances, which induce a coupling mechanism between “regular”
quantum states within and “chaotic” states outside the islands. By means of a random matrix ans...
Recent advances of radiative recombination in the presence of strong laser fields are reported. The intense laser radiation
is found to introduce new relevant features, among which enhancement and control of the emitted X-ray spectra are the most
important. The influence of the plasma medium in which the process generally takes place is considered...
Experimental investigations of the low frequency noise
of multimode 780 nm vertical cavity surface emitting lasers are
reported. Electrical noise, optical noise and their correlation
have been measured in the frequency range 1 Hz–95 kHz. The
results show that the main contribution to the electrical noise is
located in the distributed Bragg reflecto...
The conditions are found when rapid heating of the
electrons of a degenerate semiconductor in the presence of two
electric fields, one constant and the other variable, is
accompanied by the formation of a distribution function
significantly departing from the Fermi one. It is also shown that
the newly found modification of the electron distribution...
We have investigated the laser-assisted radiative recombination in the presence of a few-cycle pulse with the aim of demonstrating means of controlling such process. Within the Coulomb-Volkov approach already employed to describe the radiative recombination assisted by a monochromatic laser field, we have found that the emitted photon spectrum is a...
The explicit analytical forms of nonlinear currents in degenerate semiconductors serving as sources of coherent radiation in the wavelength millimetric and submillimetric ranges are established.
The flux density time evolution of radiation at the even harmonics frequencies of a test wave is found and its link with the evolution of the current density produced by a constant electric field is established. Even harmonics generation is studied in two regimes: that of free accelerated motion which takes place for small time intervals and that o...
The advent of the ultraintense Tabletop Pulsed Laser Systems (TPLSs) has opened new and thus for unexpected frontiers allowing
for the development and the progress of new research areas, in particular in scientific and industrial fields. Usually, these
laser systems are used in order to generate plasma on solid or gaseous targets, so-called laser-i...
We have observed various femtosecond laser-induced phenomena in glasses. We have also observed the photo-oxidation of transition
metal ions in a glass sample after the femtosecond laser irradiation. Furthermore, we have demonstrated the 3D optical memory
with ultrahigh storage density by using photoreduction phenomenon of the rare-earth ions. We ha...
The study of atoms and molecules in strong laser fields is one of the most active research areas in Atomic, Molecular, and
Optical Physics. Following extensive study over the past two decades, most phenomena involving strong fieldatom interactions
have been relatively well understood. However, there have been a number of observations suggesting tha...
In this chapter the fundamental physical processes underlying the interaction of relativistically intense EM radiation with a preformed collisionless plasma have been discussed, introducing the most appropriate relativistic models which are currently used in the theoretical research: the kinetic approach, the multi-fluid model, and the electron-flu...
A theoretical treatment of the laser-assisted radiative recombination (LARR) is presented in which the low-frequency (LF) assumption is exploited. The merit of the proposed LF approximation is twofold. First, the LF approximation considerably simplifies the calculations of the transition rates, whereas the results obtained within this approximation...
The possibility of radiation resonant transmission and reflection by a thin layer of a plasma possessing an anisotropic electron velocity distribution strongly elongated in the direction of the incident wave polarization is established.
We report on laser writing of 2D and 3D structures based on laser induced structural modifications. In our experiment, bulk glasses of chalcogenide systems Ga-Ge-S, As<sub>2</sub>S<sub>3</sub> and Ga-Ge-S thin films have been used. Photo-structuring of the bulk glasses has been obtained by using low energy (< 2.5 nj) fs laser pulses with wavelength...
A concise overview of a number of anomalous properties of hot dense nonequilibrium plasmas is given. The possibility of quasistationary megagauss magnetic field generation due to Weibel instability is discussed for plasmas created in atom tunnel ionization. The collisionless absorption and reflection of a test electromagnetic wave normally impingin...
The kink effect in low-noise pseudomorphic (AlGaAs/InGaAs) HEMT’s has been examined in detail by investigating the steady-state and pulsed I–V characteristics, the behavior of the output conductance dispersion and the performance of the gate leakage current to understand its origin. No clear evidence of impact ionization occurrence in the InGaAs ch...
Generation of high frequency radiation harmonics in a current-carrying plasma is studied. The physical mechanism responsible for harmonics generation is provided by electron-ion collisions. The current in the plasma is sustained by a constant electric field. It is shown that the electron distribution function anisotropy due to the static field yiel...
Investigations of high-frequency (HF) even-harmonics generation in a plasma embedded in a static electric field are reported. Even-harmonics generation is studied in two regimes: (i) that of free accelerated-electron motion, which takes place for small time intervals, and (ii) that of current saturation, corresponding to time moments much larger th...
It is shown that using even harmonics of a test wave it is possible to diagnose the fast time evolution of the current density.
We report on field induced inelasticity effects in state-to-state transitions caused by collisions of helium with Rydberg atoms in the presence of parallel static electric and magnetic fields. Due to the phases accumulated by the wavefunctions of the states involved into the collision events, the transition cross sections plotted as a function of t...
The basic properties of infrared laser radiation odd harmonic generation due to electron-charged impurity collisions in degenerate semiconductors are investigated. It is found that in the case of relatively weak fields, the electron Fermi distribution is the cause of an anomalous suppression of harmonic radiation. In the case of strong fields, the...
Harmonics generation of high-frequency radiation in a plasma embedded in a constant electric field is investigated theoretically. It is shown that the electron directed motion due to the static electric field yields the appearance in the plasma emission spectrum of high-frequency radiation even harmonics. The conditions are established when the eve...
Alignment and orientation effects in collisions of helium with Rydberg atoms due to the presence of static electric and magnetic fields are predicted. Analytical expressions are obtained for the cross sections of the state-to-state transitions within the manifold with the same principal quantum number. For moderate field-induced inelasticity, the c...
It is shown that in a weakly nonuniform plasma with electron heat flux the generation of odd and even harmonics of high frequency radiation is possible. The even harmonics properties qualitatively differ as compared to those of odd harmonics and depend in an essential way on the heat flux value and orientation with respect to the fundamental wave p...
A Langevin approach to understand the noise of microwave devices is presented. The device is represented by its equivalent circuit with the internal noise sources included as stochastic processes. From the circuit network analysis, a stochastic integral equation for the output voltage is derived and from its power spectrum the noise figure as a fun...
Strong-field laser-assisted radiation recombination is investigated: (a) to explore the control possibilities with two laser fields having commensurable frequencies and (b) to get some insight into the influence of the medium (a plasma) in which recombination occurs. It is found that by varying the relative phase of the two fields it is possible to...
Even order harmonics generation of the laser radiation due to electron-ion collisions in a plasma embedded in a constant electric field is investigated theoretically. Even harmonics are generated because the presence of a static electric field removes the invariance of the electron distribution function under the symmetry operation of velocity dire...
To qualify the feasibility of standard semiconductor materials and Schottky-barrier diodes (SBDs) for THz high-order harmonic generation and extraction, the harmonic intensity, intrinsic noise and signal-to-noise ratio are calculated by the Monte Carlo method when a periodic high-frequency large-amplitude external signal is applied to a semiconduct...
nterference effects caused by the simultaneous action of a two low frequency fields with commensurate frequencies during laser assisted radiative recombination (LARR) are investigated theoretically. Varying the relative phase of the two fields the following LARR features may be controlled: a) location of the maxima in the total emitted power; b) en...
The problem of laser assisted radiation recombination, taking into account the influence of the plasma in which the elementary process takes place, is investigated theoretically. Among the reported results, remarkable broadening and enhancement of the X-ray photon emission spectrum is found, provided some conditions are met. First, a sufficiently i...
The third-harmonic generation of a pump wave, resulting from the electron-ion collision frequency dependence on the electric field in the skin layer of a hot dense plasma is investigated. The relation of the current third harmonic with the high-frequency field in the skin layer is established for arbitrary ratios of the electron-ion collision frequ...
A treatment is given of harmonics generation resulting from nonlinear inverse bremsstrahlung in a plasma with an anisotropic bi-Maxwellian electron velocity distribution function. Inverse bremsstrahlung absorption of test electromagnetic wave is investigated as well.
The third harmonic generation in the skin-layer of a dense hot plasma due to inverse bremsstrahlung is investigated for regimes having increasing experimental relevance. New analytical dependencies of the radiation flux density at the frequency 3ω on the plasma and fundamental wave parameters are established.
The formation of a highly anisotropic photoelectron velocity distribution as a result of the interaction of a powerful ultrashort laser pulse with a thin foil is found to yield a large skin-layer depth and an anomalous increase of the transmission coefficient. The physical reason for the effect is the influence of the incident wave magnetic field,...
Monte Carlo simulations for high harmonic generation by two mixed electric fields linearly polarized with frequency in the far-infrared range in GaAs crystal are examined. The wave-mixed signal conversion efficiency is calculated by the use of the appropriate Maxwell equation for the propagation of an electromagnetic wave along a given direction in...
Reflection and collisionless absorption of a test wave by a plasma, with a sharp boundary and containing a small amount of hot electrons, besides the bulk of more cold electrons, are investigated. It is established that, in the high-frequency skin-effect regime, the conditions are possible, when the absorption coefficient is basically determined by...
Production of sum-frequency radiation and even harmonics from two mixed fields with frequency
in the far-infrared region, due to the nonlinearity of the velocity-field relation in Si crystal, is investigated and
compared to the relative conversion efficiency of the independent fields. The conversion efficiency of the wave-
mixed signal is calculate...
The collisionless absorption and reflection of a test electromagnetic wave normally impinging on a plasma surface are investigated within the formalism of the surface impedance. The plasma is assumed to possess an anisotropic two-temperature bimaxwellian electron velocity distribution function. Due to the wave magnetic field influence on the electr...
The dependencies of third harmonic generation due to electron scattering by charged impurities versus electron effective mass, electron temperature and infrared radiation intensity and frequency are derived. For semiconductors with strong electron effective mass anisotropy, a gigantic anisotropy in the generation efficiency is found.
The reflection of a test electromagnetic wave normally impinging on a plasma surface is investigated within the formalism
of the surface impedance. The plasma is assumed to possess an anisotropic two-temperature bi-Maxwellian electron velocity
distribution function. The linearly polarized impinging wave during reflection transforms into an elliptic...
Dense plasma heating by an ultrashort laser pulse is investigated in the regime of the high-frequency skin effect. The electron temperature evolution on the plasma surface and the properties of the classical heat transfer into the plasma interior are studied. Three possible plasma heating mechanisms are considered. At relatively not large temperatu...
A theoretical and numerical analysis of the elementary process of the laser assisted radiative recombination for the regime in which the amplitude VE of the quiver velocity of the incoming electron is equal to or larger than the average translation velocity Vq is given. It is shown that the power emitted during the laser assisted radiative recombin...
Dense plasma heating by an ultrashort laser pulse is investigated in the regime of the high-frequency skin-effect. It is shown that the diffuse electron reflection by the plasma boundary yields a significant increase of electron temperature as compared to the specular reflection case, and a faster propagation of the heat flux inside the plasma.
We investigate theoretically high-order harmonic generation in gases and show that, if the target thickness is high, off-axial phase matching is of importance. Results of a numerical study of harmonic generation that takes into account the self-action of the laser pulse are presented. We show that self-guiding of the laser pulse in a noble gas make...
We present results of analytical and numerical calculations of the
angular spectrum and the power of high-order harmonics generated with a
limited laser beam in an extended medium. It is shown that the spectrum
of harmonics generated in a thick target dramatically differs from that
of the single-atom response. In particular, in this spectrum there...
Results of analytical and numerical calculations of the angular spectrum and the power of highorder harmonics generated with a limited laser beam in an extended medium are presented. It is shown that the spectrum of harmonics generated in a thick target dramatically differs from that of the single-atom response. In particular, in this spectrum ther...
Pseudomorphic (AIGaAs/InGaAs/GaAs) HEMT's have exhibited the best noise performance over the entire LF-to-microwave frequency range if compared to MESFET's and conventional GaAs HEMT's, due to either a reduced flicker noise, a lower G/R contribution and a smaller high-field diffusion noise. We have recently investigated the microwave (up to 18 GHz)...
A treatment is given of harmonics generation resulting from
nonlinear inverse bremsstrahlung in a plasma with an anisotropic
bi-Maxwellian electron velocity distribution function. A complete
characterization of the process is reported. In particular,
analytically and numerically we established how the efficiency
of the odd harmonics generation...
The high-order harmonics generation in bulk InN, subjected to a high-frequency alternating electric field of strong-amplitude is investigated theoretically using Monte Carlo simulations of carrier interacting with a multi-mode electric field. This approach allows on the one hand to account in a natural way for the effect of the reabsorption of the...
Collisionless absorption of linearly polarized electromagnetic wave in a plasma with anisotropic bi-Maxwellian electron velocity
distribution is investigated. Due to the wave magnetic field influence on the electron kinetics in the skin layer, the wave
absorption is found to significantly depend on the degree of the electron temperature anisotropy....
We describe the linear stage of Weibel instability in a plasma heated via inverse bremsstrahlung absorption of a high-frequency, moderate intensity radiation field under conditions in which the plasma electron velocity distribution function is weakly anisotropic. We report on the possibility of a significant amplification of spontaneous magnetic fi...