We have constructed an apparatus for high-resolution electron spectroscopy and electron-ion coincidence experiments on gas-phase molecules in intense laser fields. The apparatus comprises an electron time-of-flight (TOF) spectrometer and an ion TOF spectrometer with a position detector, placed on either side of an effusive molecular beam. The ionizing radiation is either the fundamental (800 nm wavelength) of a Ti:sapphire laser or frequency doubled 400-nm light, with pulse durations of ~ 150 fs and the repetition rate of 1 kHz. We have investigated the electron emission and fragmentation of linear alcohol molecules, methanol, ethanol and 1-propanol, in laser fields with peak intensities up to ~ 1×10¹⁴ W/cm². Details of our apparatus are described along with an overview of some recent results.

We theoretically investigated the stability of highly charged fullerene cations produced with an ultrashort intense nearinfrared (IR) laser pulse (light intensity I~ 5 × 10¹⁴ W/cm² and wavelength λ ~ 1800 nm). The effects of nonlinear interactions with near-IR pulses are taken into account by combining an ab initio molecular dynamics method with an time-dependent adiabatic state approach. The results indicate that large-amplitude vibration with energy of > 10 eV is induced by impulsive Raman excitation in the delocalized h_g(1)-like mode of C₆₀ ^z+. The field-induced large-amplitude vibration of the h_g(1) mode persists for a rather long period. In conclusion, C₆₀ and its cations created upon ionization are extremely robust against field-induced structural deformation. We found that the acquired vibrational energy is maximized at T_p ~ _vib/2, where T_p is the pulse length and T_vib is the vibrational period of the h_g(1) mode. We confirmed that the vibrational energy deposited in C₆₀ can be controlled by a pulse train, i.e., by changing the intervals between pulses. Vibrational mode selectivity is also achieved by adjusting the pulse intervals.

Explosive evaporation of metallic Rb or K clusters in the presence of excited atoms stimulated by resonant CW laser radiation has been observed in a glass cell. Evaporation occurs at low laser-power density. The effect consists of the generation of optically thick and sharply localized alkali vapor clouds propagating in the cell against the laser beam. The clouds are charged and exhibit a strong luminescence of Rb or K spectral lines. The explosive evaporation of metallic clusters is explained by the laser excitation of alkali atoms, which collide onto the surface of the clusters and transfer their internal energy, which thereby causes other atoms to be evaporated and to continue the avalanche process.

A study of femtosecond laser interaction with a range of transparent solids, such as glass, sapphire, and fused silica in femtosecond-to-nanosecond time domain is reported. Time-resolved pump-probe microscopic imaging of femtosecond laser breakdown area in different transparent solids has been done. Both absorption and Femtosecond Time-resolved Optical Polarigraphy (FTOP) microscopy techniques were used. White continuum was used as a probe pulse. Strong filamented plasma absorption initially dominates, being replaced by refraction index variations in filament traces and blast wave at hundreds of picoseconds delays. Dynamics of transient absorption in K8 glass was for the first time precisely linked with the pump pulse passage observed by FTOP. Cylindrical blast wave generation was observed starting from 200 ps delays in K8 glass and silica and its velocity has been measured. Exponential decay time of laser-induced plasma in sapphire, both pure and Ti doped has been found.

A new nonlinear wave equation describing a propagation of a strong few-cycle optical pulse in isotropic dielectric media is used for an analysis of inertial polarization nonlinearity. The dependence of various inertial factors on the intensity, duration, and spectrum of radiation has been theoretically analyzed. Numerical simulation of few-cycle pulse propagation in fused silica illustrates some expected effects of nonlinear polarization inertia.

The motions of electrons driven by the fields of linearly and circularly polarized relativistically intense laser pulses are analyzed. The treatment is based on the numerical solution of Newton's equation with the Lorentz force. The electromagnetic radiation of an electron interacting with a laser pulse is studied. It is shown that this radiation comprises short pulses having the attosecond range durations. An electron which is at rest initially does not follow the figure-eight trajectories in the field of a linearly polarized laser pulse.

We show numerically that the two-photon Raman resonance in Ar⁺ ions with 24-fs and shorter laser pulses can influence strongly on spectral dynamics and efficiency of high-order harmonic generation as compared with longer pulses.

Using the analytically obtained solution of the Schrödinger equation for an electron in a quantized electromagnetic field, the ionization of an atom has been considered in the framework of a simple one-dimensional model. Expressions for the ionization rate and photoelectron spectrum have been derived and analyzed. We discuss a difference between the results obtained in the model in which the electromagnetic field is described classically and the results obtained in the model of quantized electromagnetic field. In particular, in the latter model the photoelectron spectrum can have a minimum at a certain number of absorbed photons. The minimum is a consequence of destructive interference between the contributions of two parts of the interaction operator.

We present a new class of exact nonsingular solutions for the Maxwell equations in vacuum, which describe the electromagnetic field of the counterpropagating focused laser beams and the subperiod focused laser pulse. These solutions are derived by the use of a modification of the "complex source method", investigated and visualized.

Modifications of temporal parameters of ultrashort laser pulses (USP) with intensity more than 10¹² W/cm² and duration not less than 700 ps, reflected from boundary "air-plasma" and emitted by the neodymium superregenerator are investigated. We explain shortening of pulses by Doppler effect originating in plasma that results in occurrence in it of properties of an abnormal dispersion. Designed circuits of a superregenerative amplification of a USPs appeared fit for examination of high-speed processes in the plasma excited in air, and also for production of polyatomic carbon compounds (fullerenes).

Two-photon transitions between the perturbed 6s^{2 1}S₀ ground state and the perturbed 5d7s³D₂ state of a Ba atom have been experimentally investigated with different perturbing and exciting radiations. A strong dependence of the probability of two-photon transitions between these perturbed states on the mutual orientation of the electric vectors of the exciting and perturbing radiations has been found.

The process of formation of doubly charged ions upon multiphoton ionization of barium atoms by linearly and circularly polarized radiation of dye lasers is studied in the frequency range from 16 600 to 17 900 cm^-1. A large number of resonance maxima in the yield of Ba⁺ and Ba²⁺ ions were observed upon tuning the radiation frequency. It is unambiguously proved that most resonance maxima in the yield of Ba²⁺ ions are associated with the resonance transitions in the spectrum of Ba⁺ ions. This fact confirms the cascade mechanism of formation of Ba²⁺ ions in the frequency range of localization of these maxima. But the number of the resonant maxima in Ba²⁺ ions yield do not identified by transitions both in spectra of Ba atom and Ba⁺ ion. This fact indicates on realization of the noncascade mechanism of Ba²⁺ ions formation in the frequency range of these maxima.

The non-stationary problem of electron-molecular ion scattering is solved analytically in the frame of the perturbation theory on the scattering potential and without the plane wave approximation for the incident electron. The influence of the parameters of the incident electron wave-packet on the observed diffraction images is studied. Effect of interference between incident and scattered wave packets is analyzed in details and shown to result in dramatic changes of the angular distributions.

It is argued that, unlike the case of the mutual trapping of several light beams, the selftrapping of a single light beam in the vacuum due to vacuum polarization would require the field strengths much greater than 10¹⁶V/cm and hence can not be observed in the foreseeable future.

The probabilities of photoionization by the black-body radiation (BBR) were calculated for singlet and triplet S-, P-, and D-Rydberg states of a neutral helium atom. The numerical values obtained on the basis of the Fues model potential for states with the principal quantum number n ranging from 8 to 45 were used to derive a formula which not only reproduces the asymptotical behavior of the ionization rate for n → ∞ but also describes exactly its maximums. The n-independent constants in this formula are determined by a third order polynomial in powers of the absolute temperature with coefficients derived from the calculated data for the temperature range from 200 to 2000 K.

A behavior of nanostructured conducting Lengmuir - Blodgett films and nanoporous alumina in resonant electromagnetic fields was investigated. To describe interaction between an intensive electromagnetic field and the nanocomposite, a behavior of metal atom, which is disposed in a nanobubble, in a resonant electromagnetic and slowly varying external magnetic fields taking into account of a self-consistent electromagnetic field of matrix was examined. The performed description has allowed to conclude about possibility of mixing states in such nanocomposites under action of oscillating magnetic fields.

Excitation of low-lying nuclear levels by inelastic scattering of laser-accelerated electrons was considered. The process has a threshold dependence on the laser intensity. The estimates give a short-term activity of certain isotopes up to 10³ Cu for 10-fs laser pulses with energy 3 J for concentration of this isotope in the gaseous target about 10²⁰ cm^-3.

This study is devoted to investigation of femtosecond laser radiation parameters (intensity, contrast, polarization) influence on properties of hot electron population of dense plasma created at the surface of melted metal target.

We present the results of our experiments directed to the suppression of atmospheric gases influence on delivering of superintense femtosecond laser radiation to solid target at atmospheric conditions.The suppression of atmospheric gases effects is attained by expositing the target to a double-pulse radiation and caused by reducing gas density near the target surface). In our scheme the first pulse (nanosecond UV pulse from XeCl excimer laser) acts as a vacuum pump. The second laser pulse (tightly focused femtosecond pulse) delaying up to several microseconds respect to the first laser pulse delivers the basic energy necessary for switching a hot plasma on the target surface. We have observed the maximum X-ray yield increasing up to 17 times under double pulses exposure compare with the single femtosecond pulse regime.

The semiclassical theory of laser cooling is applied for the analysis of cooling of unbound atoms with the values of the ground and exited state angular moments 1/2 in a one-dimensional nondissipative optical lattice. We show that in the low-saturation limit with respect to the pumping field a qualitative interpretation of the cooling mechanisms can be made by the consideration of effective two-level system of the ground-state sublevels. It is clarified that in the limit of weak Raman transitions the cooling mechanism is similar to the Doppler mechanism, which is known in the theory of two-level atom. In the limit of strong Raman transitions the cooling mechanism is similar to the known Sisyphus mechanism. In the slow atom approximation the analytical expressions for the coefficients of friction, spontaneous and induced diffusion are given, and the kinetic temperature is estimated.

A semiclassical theory of superradiant scattering from Bose-Einstein condensate of dilute gas without the mean- field approximation is proposed. Solutions of the system of Maxwell-Schrödinger equations describing this effect as well as the coherent reflection of light and the backward amplification of matter waves are obtained.

The interaction of a linear polarized weak probe wave with the molecular iodine driven by the strong pump wave with the orthogonal polarization is experimentally studied. An effect of electromagnetically induced transparency (EIT) is observed. The group velocity of the probe wave is decreased to 0,13c.

High fidelity, high count rate four qubit linear cluster states have been realized by using two photons that are entangled both in polarization and linear momentum. Their properties have been investigated by evaluating the entanglement witness and carrying out a "stronger two observer all versus nothing" test of quantum nonlocality. The experimental results concerning the realization of single qubit rotations demonstrates the feasibility of one-way quantum computation by using these states.

We consider possible ways to recognize multi-photon entangled states in experiment. A commonly used technique is to measure higher-order multi-photon correlation functions and their dependence on certain phase delays (multi-photon interference). Theoretically and experimentally, we show that multi-photon interference can have very high visibility for classical sources: up to 81.8% in the three-photon case and up to 94.4% in the four-photon one. Therefore, the visibility of multi-photon interference should not be used as a criterion of multi-photon entangled states generation. Instead, we suggest to characterize multi-photon entanglement by the photon-number dependence of the normalized correlation functions.

We present a detailed analysis of the coherent backscattering spectrum of two atoms. We identify frequency domains where the interference contribution can be positive or negative, or exhibits dispersive features, and explain these distinctive features.

We have investigated the propagation of plane waves through one-dimensional superlattices composed of alternate layers characterized by two di.erent refractive indexes, which may take on positive as well as negative values. For both indices of refraction positive we have found null-gap points for commensurate values of the optical path lengths of each layer at which the superlattice becomes transparent. We have determined the symmetry properties of the electromagnetic field demonstrating the degeneracy of the solutions at these points. Furthermore, we have been able to characterize non-Bragg gaps that show up in frequency regions in which the average refractive index is null, by obtaining analytically the non-Bragg gap width which depends only on the ratio ^b/_a of the layer widths.

Quantum dynamics of an interaction of an elementary photodetector with multiphoton states of electromagnetic field is discussed. Some nonlinear processes during the elementary detector operation are considered.

Under conditions of intracavity laser pumping of the absorbing cell the possibility of high-temperature BEC-like phase transitions in polariton assemble is shown. It manifests in spectral features of the field-matter-cavity system and results in the "spectrum" condensation.

Zero-point quantum fluctuations in a medium with oscillation of optical length in time cause spontaneous two-quantum emission of light. This emission is usually very weak, but it strongly enhanced if a resonance condition for frequency and amplitude of the oscillation is fulfilled.

In continuation of our previous works, systematic investigation of the magneto-optical (MO) resonances from the ³P₁(1s₄) (Pashen notation), ³P₂ (1s₅), and ³P₀ (1s₃) levels of NeI was carried out. This study aims to clarify the formation mechanisms of the neon 1s_i (2p⁵3s) states coherences. Anomalous MO resonances are experimentally observed and the possible mechanisms of their creation are discussed.

Analytical dependences on a static electric field F₀ are derived for the wave functions, matrix elements and probabilities of radiation transitions between multiplet substates interacting in field in pairs, ranging from ordinary doublet states with spin S=1/2, pair-wise interacting sublevels of triplet and quintet states with the magnetic quantum number M=0, to the most general case of states with arbitrary angular L and spin S momenta and maximal magnitude of the magnetic quantum number |M|=L+S-1. Equalization of doublet line intensities in the anticrossing field region and vanishing of one of the two doublet lines in the high-field regime are demonstrated. A general relation is determined between the anticrossing field F_A, multiplet splitting and tensor polarizability.

The Bose-Einstein Condensation (BEC) of the two-dimensional magnetoexcitons on the superposition state is studied. The superposition of two excitonic states formed by electron and hole on the lowest Landau levels (0, 0) and on the first excited Landau levels (1, 1) was considered. The generalized Bogoliubov u-v transformation was deduced. The criterion on the exciton concentration was established. The influence of the BEC on the absorption band shape is discussed.

Optical activity of atomic medium with interfering laser induced continuum structures is studied theoretically and illustrated by the example of hydrogen. The optically active region in the atomic spectrum is scanned by linearly polarized probe field whose polarization properties are changed by the medium. Analytical equations for acquired ellipticity and polarization plane rotation are obtained. They demonstrate that the optical activity is a non-trivial function of the parameters of the driving laser fields. Numerical results are presented for the VUV probe radiation with two circularly polarized lasers, coupling the hydrogen Ep continuum with the 2s and the 5s, 5d states, respectively.

We consider the influence of an operational pulses' shape and Rabi frequency on the accuracy of implementation of quantum repeater protocol on based NV+¹³C centers in diamond. It is shown that rectangular pulses with properly chosen Rabi frequency provide the best quality of operations over the center.

The problem of entanglement distribution between distant cites (laboratories) is considered for the states, composed by linear superposition of coherent states with opposite phases. The protocol based on transmission of ancillary field with small amplitude is proposed.

A bipartite, arbitrary-dimensional entanglement measure based on local correlations of any set of generators of the corresponding algebras is proposed. An explicit relation with the I- and 3-concurrences for pure states, and a limit for entangled mixed states, are given.

In this paper we will present some of the work performed at INRIM on the application of quantum optical states to quantum information and metrology. In particular we will consider some specific tools needed for quantum information researches as the characterization of the quantum optical states, communication lines and detectors. In little more detail, after a general presentation of the activity of our lab, we will describe a series of experiments where we have reconstructed the statistics of various quantum optical states with an innovative method based on a "variable" quantum efficiency of detectors. The success of the presented applications and the simplicity of the method suggest a possible widespread applicability of it. We will then describe our work on photo-detectors calibration by exploiting PDC light and in particular the extension to analog detectors. Finally, we will mention some research in progress on the effects of the communication line (fiber, open air) on the transmitted quantum state.

An effective and robust method for generating random bits from random time intervals between quantum jumps of optical field is proposed and experimentally tested with spontaneous switchings in a bistable vertical-cavity surface-emitting laser. This algorithm allows one to avoid the problem of biasing in the output bit stream as well as to obtain low correlation between generated bits. A comprehensive comparative statistical analysis of different methods of extraction of random bits from experimentally measured time intervals between spontaneous polarization switchings in a bistable vertical-cavity surface-emitting laser shows the advantage of the proposed method.

The quantum key distribution protocol ΒΒ84 combined with the repetition protocol for error correction are analyzed from the viewpoint of security against individual eavesdropping empowered by quantum memory. We show that a mere knowledge of the error correction protocol changes the optimal attack and provides the eavesdropper with additional information about the generated key.

The phase sensitivity of the atomic ionization by intense one-cycle linearly polarized laser pulses has been discussed within the analytic Landau-Dykhne approximation. The generalized Keldysh parameter has been introduced for analysis of two regimes of ionization. In the case of super-intense laser field we found that ionization by cosine waveform pulse is much more effective than that by sine waveform pulse with the same energy in the pulse. This is pure quantum destructive interference effect. Electron energy spectra and effective electron temperatures are also derived analytically for both waveform pulses.

The results of numerical simulation of two-photon resonance generation and propagation in Ar+ of single attosecond pulses at two-photon self-induced transparency are presented.