This PDF file contains the front matter associated with SPIE Proceedings Volume 6614, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We report a front-end system that provides selection, stretching and amplification of 240 fs pulses from sub-nJ level up to 5 mJ with contrast ratio >10⁷. Laser system consists of a master oscillator GLX-200, single pulse selector, diffraction-grating stretcher, regenerative amplifier and electrooptical deflector. It is shown that spectral shaping reduces spectrum narrowing in amplifier . This system will be used for seeding a powerful CPA laser chain.

A prism/grating aberration-free stretcher for OPCPA system with chirp reversal is presented. A designed stretcher with a conventional grating compressor allows to accurately compensate the residual dispersion of the system up to the 4-th order inclusive. The peak power of 200 TW in the 45-fs pulse at the output of the OPCPA laser was achieved.

A development of a method for analysis of diffraction grating with a multilayer dielectric coating is presented. The new method enables the calculation of the diffraction efficiency and damage-threshold for the wide area of the depth to period ratio. It is shown, that the high efficiency diffraction grating with high damage-threshold may be produced. This problem may be resolved by using of relatively deep holographic gratings with multi-layered dielectric coating and by using of different thickness of dielectric layers in different pares of layers.

The influence of small mutual displacements and turns of diffraction gratings that make up a compound grating on their summary reflected wave intensity in the Littrow mount was theoretically studied. It was shown that these displacements cause phase shifts between diffraction waves reflected by different gratings, that can considerable decrease their summary wave intensity. The admissible limits of displacements and turns, that enable to obtain maximum summary wave intensity were determined. The phases of diffracted waves were calculated on the base of coupled integral equation method.

Mode structure and nonlinear dynamics of the chirped pulse are studied in the graded-index optical fiber with a longitudinal inhomogeneity of the refractive index. Chirps are classified with respect to the relationship between the depth of the linear frequency modulation and the width of the pulse spectrum. Considered in the paper are the regimes: (1) the modulation depth essentially less than the spectrum width - chirped pulses; (2) the depth of modulation is commensurate with the width ofthe pulse spectrum - strongly chirped pulses. The pulse propagation is modelled with a nonlinear wave equation in which the refractive index depends quadratically on the wave field. This equation is solved asymptotically with two different ansatzes for chirp and strong chirp regimes. The mode structure ofthe pulse is shown to differ for chirped and strongly chirped pulses, and in both cases relationships are stated confining the coefficient of the linear frequency modulation with the phases of high-frequency carrier and envelope. Consequent asymptotic procedure leads to the nonlinear equations governing the dynamics of the envelopes of chirped and strongly chirped pulses. Studied in more details is the envelope of the chirped pulse, in this case some additional assumptions on the longitudinal inhomogeneity of the optical fiber enable to reduce the equation for the envelope to the second Painleve equation. Comparison with sech-soliton of the nonlinear Schroedinger equation is carried out and important features conditioned by the linear frequency modulation are ascertained.

Using computer simulation, we investigate an optical wave formation in optical fiber with cubic nonlinearity under the influence of time dispersion of nonlinear response. We show possibility of attosecond pulses train formation at the shock wave front. This train takes place if time dispersion ofnonlinear response influences significantly on laser pulse propagation in optical fiber. The influence of frequency modulation is considered as well. Our analysis is based on original transform of well-known generalized nonlinear Schrodinger equation with temporal derivation from nonlinear response. We analyze the influence of weak temporal dispersion and weak second order dispersion on propagation of picosecond (or femtosecond) pulse with low intensity in nonlinear optical fiber. Under such conditions the formation of train sub-pulses, which duration is from ten to fifty times shorter than input pulse duration, are obtained. We investigate dependence of distance of train pulse formation on dispersion coefficient, coefficients characterizing nonlinearity and dispersion of nonlinear response. For computer simulation we use conservative difference schemes, which allow us to make simulation with big accuracy.

A nonlinear wave equation suitable for describing a propagation of a light pulse containing few oscillations of a strong electric field in isotropic dielectric media is deduced. It describes non-resonant dispersion of linear refractive index and non-inertial third-order non-linearity as well as inertia of dielectric non-linearity of electron nature, including parts caused by energy state population dynamics and free electron motion. The dependence of the conditions for the dominance of different physical factors in the self-action of few-cycle optical pulses in dielectrics on the intensity, duration, and spectrum of radiation has been theoretically analyzed. It is shown that the larger the pulse width and the central wavelength, the stronger the effect of plasma nonlinearity. For example, for a quartz glass in the field of pulses with a duration of 10 fs and a central wavelength of 780 nm, this nonlinearity mechanism is dominant at intensities exceeding 3 - 10¹³ W/cm².

We have demonstrated the sub-10-ps time-resolved measurement of the x-ray absorption fine structure (XAFS) in laser-excited Si foil by using a femtosecond laser-produced plasma soft x-ray as a probe. We observed a rapid change and recovery in the absorption structure near its L_II,_III edge induced by 100-fs laser pulse irradiation when the laser intensity was in the 10⁹-10¹⁰ W/cm² range. When the incident laser intensity was of the order of 10¹² W/cm², which is higher than the damage threshold, the extended x-ray absorption fine structure (EXAFS) signals clearly revealed inter atomic distance expansion and structural disordering as well as a change in the electronic structure caused by the production of liquid Si. We also describe our recent results on spatio-temporally resolved soft x-ray absorption in an expanding ablated particle cloud from aluminum that was heated with a 10¹⁴-W/cm², 100-fs laser pulse by using an imaging system for time-resolved soft x-ray absorption spectroscopy.

The generation of ultra-intense laser pulses is very important in a number of scientific and technical applications, such as plasma accelerators, x-ray lasers, etc. Present Nd:glass lasers are able to deliver sufficiently large pulse energies because a big diameter of their final amplifier aperture and enough high damage threshold of glass for nanosecond laser pulses. However, the damage threshold decreases with the laser pulse duration and, therefore, nanosecond multi kilo-joule laser pulses have to be compressed without a losses of energy and beam quality after the end amplifiers to obtain the required ultra-intense sub-picosecond pulses. The standard technique to reach maximal laser peak power by reducing its pulse length at a given energy is the CPA-scheme [1] in which the laser pulse is stretched, amplified, and compressed by dispersive linear optics. CPA-based optical systems have been able to produce petawatt (PW) laser pulses. The pulse energy is limited by the thermal damage of the optical elements, especially the compression gratings, which for kJ applications have to be very large and therefore extremely expensive. One possibility would be to develop less expensive large-size compound gratings or one could, perhaps, significantly increase the damage threshold of the gratings by multi-layer dielectrics [2] or even using plasma gratings [3]. In the last case back reflection of a short, intense laser pulses at oblique incidence on solid targets is explained with a model where a periodic electron density modulation acts as a diffraction grating. The pump and reflected electromagnetic waves drive through the ponderomotive force the grating and the overall system becomes parametrically unstable. The instability is shown to saturate at some level, because the higher harmonics in the electron density modulation turn the diffraction more diffuse thus reducing both the sustaining ponderomotive force and the back reflection coefficient. The calculated reflection coefficient value is close to the experimental one at the same conditions [4]. We considered the conversion of pump laser long pulse energy into seed short pulse energy on surface plasma gratings. The optimal conditions for maximal conversion efficiency into a back reflected pulse are found. The analytical model and numerical code, which simulate and explain the processes were developed. The result of calculations show that at short plasma length and the optimal parameters of plasma grating the diffraction efficiency can be enough high and such gratings can be used for laser pulse compression.

It was found that maximum particle output and best possible spatial uniformity of proton beam took place for two-layer target when the front layer was the high-Z film. It was shown that the ion radiography of the convenient objects with using the two-layer targets allow to get the projecting pictures with high spatial resolution that was about one micron. Threshold spatial sensitivity of proton radiography is estimated.

The investigation of the transition radiation of the laser plasma electrons is an important physical problem, because the radiation spectrum contains the information about the function of fast electrons' distribution, about the structure of target surface, and about the distribution of density and of electromagnetic fields nearby the target surface. The transition radiation is the additional mean of target diagnostics and makes it possible to determine experimentally the parameters of ions' acceleration in laser plasma [1-5] and the parameters of fast electrons, which generate the X-rays [6-8].

Development of highly effective debris free EUV (extreme ultraviolet) radiation source is an actual problem today. Experimental results on EUV output from the source based on laser-produced plasma in supersonic Xe jet have been obtained. The conversion efficiency is 0.08% at a wavelength of 13.5 nm (Δλ = 0.35 nm, 2π sterrad). The methods of optimization of gas-jet converter have been determined. Measurements of EUV radiation energy dependence on the laser energy and the target material (solid-state Cu, Mo, W, Ta and supersonic Xe jet) have been made. The conversion efficiency of laser-produced plasma (CELPP) has been determined and the experimental values have been obtained for different materials of the target.

The conversion efficiency of laser radiation into EUV radiation was obtained for the Tin plasma target. The plasma is the result of radiation-with-matter interaction using Nd-glass and CO₂ laser. Numerical simulations of target plasma parameters were made with the help of a one-dimensional and two-dimensional radiation hydrodynamics codes.

The numerical calculations of the spectrum of nonlinear polarization for 3- and 4-level system in femtosecond pulses have been made. The strong field interaction is responsible for coherence transform, red -, blue shifts and splitting on the spectrum. The reverse Fourier transform for restore of time domain is proposed for dephasing rate determination. The comparison with experimental results for complex molecules and semiconductors has been made.

Physical aspects of resonance effects arising in plasma due to interactions of nuclei with the electrons are considered. Among them are resonance conversion (TEEN) and the reverse process of NEET. These processes are of great importance for pumping the excited nuclear states (isomers) and for accelerating their decay. Experiment is discussed on studying the unique 3.5-eV^229m Th nuclide.

The decay of a pure nuclear exciton (immobile collective excitation), created by a pulse of synchrotron radiation, is analyzed. It is shown that in the later phases of the decay, the exciton becomes localized at the sample's frontal surface. Inside the sample, the secondary gamma-quanta, emitted by the contracting exciton, are converted into the polaritons (mobile nuclear excitations), characterized by different frequencies and equal group velocities. On the sample's back surface, the polariton interference causes a beating structure of the transmitted radiation, observed in experiments.