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This paper considers various channels of y-quantum generation via an ultra-short high-power laser pulseinteraction with different targets.We analyse the possibilities to create a pulsed y - radiation source usinglaser triggering of some nuclear reactions and isomer targets. It is shown that 0.2 MeV monochromaticshort pulse ofy - radiation can be obtained with pulse energy sub-mJ level from isomer atoms localizedin a magnetic trap. For nuclear reaction channel in light- atom materials, it is shown that 100-TW laserpulse gives rise to formation of about io6 photons near 5 MeV energy. 1. Introduction To date, many physical problems call for using a sources of'y -radiation and vast scope of theseproblems ranging from non destructive gamma flaw detection to medical examinations[1I. It should benoted that, presently, the intensity of ordinary radioactive sources cannot be higher than 10-100 GBk,whereas much higher intensity is necessary for many investigations.Commonly, synchrotron radiation is used as a high-intensity y -source, its activity being about PBk.However, significant success notwithstanding, the use ofthe synchrotron radiation as a y -sourcefeatures some essential drawbacks. First, it is impossible to obtain the high intensity 'y -radiation in verynarrow frequency range, because the synchrotron radiation spectrum is continuous. Hence narrow-frequency-band experiments with a high-power y -source appear to be impossible, because the power of

The results of Monte-Carlo modeling of volume and spark ignition of spherical laser targets are systematized and the critical parameters are obtained both of isobaric and of isochoric central ignitors. It is shown that the target thermonuclear (TN) burning is independent on ignitor present if the ignitor dimension and temperature lower than the critical ones. In the opposite case TN flash result in effective burning with gain G-100, and the TN energy release is practically independent on the further increase of ignitor parameters. The intermediate gains 1 < G < 100 are obtained in rather narrow range of ignitor parameters near the critical. It is shown that the values of critical ignitor parameters are very sensitive to the way of ignition. The critical dimensions of isobaric ignitors are greater by several fold than ones of isochoric ignitors. On the contrary the overcritical target gain is practically independent on ignition origin and may be evaluated with a good accuracy by the simple asymptotic expression. The isochoric spark ignition associated with the fast ignition scheme is considered in detail and evaluations of minimum energy absorbed by extra laser pulse in terms of energy absorbed by basic driver are presented.

One of the most interesting effects predicted by quantum electrodynamics is photon-photon scattering, and thecause of it is vacuum polarization. This phenomena was successfully studied since 1930th [6]. Now the scientificinterest to these processes experiences a new rise. And the reason is following: development of high-power laserswith femtosecond pulses of petawatt power made actual the investigation of influence of vacuum polarization onparameters of radiation.The central effect of vacuum polarization is the electron-positron pairs production in the strong light fields.Although modern lasers are unable yet to produce them and the maximum of this phenomenon is laying in the

Femtosecond laser produced plasmas emit radiation in a wide spectral range and, in particular, they show strong emission in the water window (2.3 - 4.4 nm).

Numerical simulation of thermonuclear flash with isobaric ignitor for laser spherical targets with different dimensions and temperatures are performed and the target energy gain as a function of ignitor parameters is obtained. As a result the requirements for ignitor parameters are elaborated under which the spark ignition provides an essential increase in the gain as compared with volume ignition. Calculations are carried out with the use of TERA code based upon self-consistent solution for system of kinetic equations for thermonuclear particles and radiation, obtained by the Monte Carlo method, and of hydrodynamic equations.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In result of numerical and analytical consideration is shown, that the essential part electrons, having been in area undercritical density, under action of arising forces is formed in clots and takes off for vacuum in a direction, different from normal to a normal of a surface in a narrow interval of corporal corners. The received results provide an opportunity of laser electronics acceleration at reflection USLP from a flat target.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work we consider a possibility of pulse (gamma) - source creation for atoms of nuclear isomers localized in a magnetic trap. It was shown, that in this case we can obtain a (gamma) -radiation pulse duration of 102-103 picosecond with a pulse energy about 10-3.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The use of self phase modulation for spectrum broadening with subsequent pulse compression by diffraction gratings allow to compress high energy laser pulses in wide range of pulse lengths. We have discussed different feasibility of such method for pulse shortening.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We performed computer simulation of the amplifier tract of a terawatt picosecond laser with pulse compression by means of our 3-D computer code PIKA. Parameters of the laser system on Nd-glass for obtaining subpicosecond pulses were determined. Our computer code VERA was used for simulation of a compressor based on holographic metallized gratings with dielectric coating and increased damage threshold.

While the optical breakdown of transparent dielectrics for nanosecond and longer laser pulses is well investigated theoretically and experimentally, the breakdown in a field of picosecond and femtosecond pulses has not been adequately explored. At the same time such investigation presents scientific interest, because short pulse duration can make some change for a mechanism of the optical breakdown. Also these data have practical importance for high energy laser development and management of temporal parameters of a pulse. Thus we have carried out measurements of the damage thresholds for pulse durations 450 ps and 3 ps (FWHM) for fused silica. Theoretical analysis is presented to explain experimental results. The possibility of applying the optical breakdown for pulse shortening is discussed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The recent development of ultra-short pulse lasers has made possible the investigation of laser matter interaction at ultra-high intensities. For sub-picosecond pulses, a hot and overdense plasma is produced very rapidly during the rise of the pulse and further laser interaction occurs with this plasma. One of the results of the interaction is the generation of fast electrons and of intense hard x-ray emission. The x-ray pulse duration is determined by the mean free path of the fast electrons in the target material. It can be very short (< 1 ps) and its intensity sufficient to be registered by the usual methods. With high laser pulse repetition rates, it has been demonstrated [1] that one can obtain an instantaneous signature of fast-x-ray dense-matter interaction processes. The high energy of the x-ray photons (up to ≈ 1MeV) makes it possible to study small size objects and even to excite nuclear levels. Numerous papers [2-7] have been devoted to the study of femtosecond laser pulse interaction with plasmas. In this paper, we calculate the electron energy distribution function in the presence of the laser field, the absorption coefficient, and the parameters of the fast electron flux in the plasma. Our absorption results are in agreement with previously published [3-5] papers. A new feature of our calculations is the determination of the energy and spectrum characteristics of the hard x-ray pulse produced by the interaction of an intense laser with a solid-state target.

We present observations of intense beams of energetic negative hydrogen ions and fast neutral hydrogen atoms in intense (5 × 1019 W/cm2) laser plasma interaction experiments, which were quantified in numerical calculations. Generation of negative ions and neutral atoms is ascribed to the processes of electron capture and loss by a laser accelerated positive ion in the collisions with a cloud of droplets. A comparison with a numerical model of charge exchange processes provides information on the cross section of the electron capture in the high energy domain.

The scenario of “electron capture and loss” has been recently proposed for the formation of negative ion and neutral atom beams with up to MeV kinetic energy [S. Ter-Avetisyan, et al., Appl. Phys. Lett. 99, 051501 (2011)]. Validation of these processes and of their generic nature is here provided in experiments where the ion source and the interaction medium have been spatially separated. Fast positive ions accelerated from a laser plasma source are sent through a cold spray where their charge is changed. Such formed neutral atom or negative ion has nearly the same momentum as the original positive ion. Experiments are released for protons, carbon, and oxygen ions and corresponding beams of negative ions and neutral atoms have been obtained. The electron capture and loss phenomenon is confirmed to be the origin of the negative ion and neutral atom beams. The equilibrium ratios of different charge components and cross sections have been measured. Our method is general and allows the creation of beams of neutral atoms and negative ions for different species which inherit the characteristics of the positive ion source.

Ion acceleration phenomena at relativistic intense laser interaction with thin foil targets are studied to find an efficient laser-target interaction concept at the conditions, where neither the ponderomotive pressure of the laser light nor the hot electron pressure is negligible. Particle in cell simulations and the analytical model are allowing to predict optimum laser-target parameters and suggesting a significant increase of proton energy if a hybrid proton acceleration scheme is used. In the proposed scenario, the laser polarisation is changed during the acceleration process: First with circularly polarised laser light the target is accelerated as a whole by the ponderamotive pressure, and then with linearly polarised laser light the electrons are heated which additionally increases the accelerating field. The calculations are in good agreement with experimental findings.

A possibility for compression of self-modulated pulses with Joule energy and duration about 1 psec to durations lessthan 100 fsec is shown. Variation ofthe compression degree and of contrast of such pulses was studied in dependence on their shape, parameters of the medium, type of applied compressor, and limitations by competing nonlinear processes. The effect of supercompression of self-modulated and modulated pulses by means of a compressor of aspecial type was found. The possibility of SBS compression of laser pulses with super-high power was found.Keywords: pulse generation, CPA, phase modulation, supercompressionI. INTRODUCTIONAt present, application of the technique for chirped pulses amplification made possible to create compact solid-statelasers that give ultrashort laser pulses with superhigh intensity."4 The basic scheme of such lasers includes thefollowing stages: generation of short pulses with low energy; expansion and chirping; amplification up to considerable energy; and, finally, compression to durations comparable with initial one and reaching high powers.Initially, pulse expansion was performed in fiber light guides by means of nonlinear phase modulation.' Later, othermethods with application of diffractive gratings appeared. They permitted to advance to the domain of shorter pulses.At present, the shortest pulses (< 0.1 ps) were obtained by application of spectral broad-band crystals, such as TiA12O3or LiSAF, and the pulses with the highest energies (duration I ps) -byapplication of Nd glasses. The authors of Ref.20 proposed additional compression of picosecond pulses of considerable energy by means of nonlinear phase

We have found out that in the case of the laser pulse with pico- or subpicosecond duration its energy part, scattered via SBS in the strongi y i nhomogeneous short p1 asma, reaches the val ue of fracti on of percent for the intensity of W/cm2 , if there is rio prepulse, and for the intensity of 1O W/cm , if such a prepulse is pr esented . Thi s fact may be of use i n the exper i mental eval uati on ofthe pul se contrast val ue and influence. I NTRODUCTI ON The development of CPAbased (Chirped Pulses Amplification) lasers made possible the generation of super-intensity ultrashort pulses and I t was i nduced the great i nterest to the investigations f distinctions of nonlinear interaction of the pulses with the plasmaThe stimulated Briliouin scattering (SBS) is fundamental nonlinear process with low threshold by comparision and which is determiriatedeasily in the experiments. The SBS was investigated in detail for the 1 ong pul ses' . The anal ysi s of the SBS I n undeense p1 asma for the

Hot electrons and hard x‐ray pulses produced by the interaction of strong laser radiation with an underplasma is analytically and numrically investigated. The distribution function and parameters of the fast particles are determined, and the energy and spectrum of hard x%‐ray pulses are calculated. (AIP)

The theoretical results have been compared with experiments carried out on laser plasma source. A significant role of the tail of the asymmetric subnanosecond pulse, that change noticeably the charge composition, was shown.

We regard the amplification of Stokes pulses with diffractional divergence for stimulated Brillouin scattering compression in multimode pump irradiation. It is demonstrated the possibility of effective compression up to nanosecond duration with conservation diffractional quality Stokes pulses or anti-phase conjugation, into pump range from tens up hundreds jouls which is comprehensible for experimental testing.

Phase modulation interferometer with the phase difference computed from the ratio of the first and second harmonics amplitudes has been developed. Signal distortions and deviations of measuring conditions against normal conditions are analyzed and appropriate corrections are made. The instrumental error of small displacement measurements is equal to +/- 0.8 nm (0.95). The digital readout interval is of 1 nm.

In recent years new high-intensity subpicosecond lasers allowed to investigate property of matter in ultrahigh electromagnetic fields. In this work the electron motion equations in field of three orthogonal standing waves is being solved. This solution was obtained by method of average Hamiltonian, when the electron velocity in laser field v E equals eE 0 /m(omega) is less than light velocity c ((omega) - laser frequency).

The linear problem of p-polarized laser radiation absorption in sharp-edged plasmas under the normal skin-effect regime was considered. Magnetic component equation has been solved analytically by the use of perturbation techniques in the limit when the density scale length is much less than the laser wavelength. Asymptotic expressions for an absorption efficiency have been obtained for a linear plasma density profile.

It’s shown that the imposition of sub-laser wavelength relief structures on the surface of mass-limited-targets results into several folds higher short-pulse laser absorption, and consequently the efficient generation of fast ions. The optimum relief parameters for enhanced short-pulse laser absorption and higher ion acceleration are estimated numerically by particle-in-cell simulations and then corroborated by analytical scalings. The stability of the pre-imposed surface modulation during the laser pulse foil interaction is also examined.

Ion acceleration resulting from the interaction of ultra-high intensity (2 × 1020 W/cm2) and ultra-high contrast (∼1010) laser pulses with 0.05–10 μm thick Al foils at normal (0°) and 35° laser incidence is investigated. When decreasing the target thickness from 10 μm down to 0.05 μm, the accelerated ions become less divergent and the ion flux increases, particularly at normal (0°) laser incidence on the target. A laser energy conversion into protons of ∼6.5% is estimated at 35° laser incidence. Experimental results are in reasonable agreement with theoretical estimates and can be a benchmark for further theoretical and computational work.

MeV negative oxygen ions are obtained from a water spray target irradiated by high intensity (5 × 1019 W/cm2) and ultrashort (50 fs) laser pulses. Generation of negative ions is ascribed to electron-capture processes that the laser-accelerated high-energy positive ion experiences when it interacts with atoms in the spray. This mechanism implies the existence of a large number of MeV neutral oxygen atoms, which is consistent with indirect experimental evidence.

The proton acceleration from a thin foil irradiated by a laser pulse at relativistic intensities is a process highly dependent on the electron dynamic at the rear side of the foil. By reducing the lateral size of the laser irradiated foil the hot electrons are confined in a small volume leading to an enhancement of both the maximum proton energy and the conversion efficiency in the target normal sheath acceleration regime. In this paper we demonstrate that an optimal lateral size of the target can be found. While a smaller target surface leads to a better hot electron confinement and enhances the Debye sheath accelerating the protons, it also leads to an increase of preplasma formation due to limited laser contrast available experimentally and hence to a decrease of the proton acceleration. The experimentally found optimum is in good agreement with analytic theory and 2D particle in cell simulations. In addition, the maximum proton energy as a function of pulse duration has been investigated. The experimental results fit to an analytical model.

The interaction of high-power femtosecond laser pulses with matter has now become an important field of study, as the advent of high-power short-pulse laser systems offers the chance of studying a completely new and very complex regime of laser plasma generation. In this paper the results on conversion efficiency into X-ray are presented for a broad range of experimental parameters. The situation is studied, when the contrast of laser pulse is sufficiently high, i.e. the prepulse is eliminated. The results are then compared with the experimental data. We pay the main attenuation on the regime of normal skin-effect in contrary of our previous report.

Various regimes of interaction of ultrashort laser pulses with solid targets in vacuum are analyzed. Analytical formulas that characterize plasma parameters and x-ray emission during the laser pulse are obtained in a very broad range of experimental parameters. For constant laser energy, the conversion efficiency into x rays during laser pulse is shown to grow with laser pulse length in all interaction regimes.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on our experiments on laser-driven ion acceleration using fully isolated mass-limited spheres with a diameter down to 8 μm for the first time. Two-dimensional (2D) particle-in-cell (PIC) and hydro-code simulations were used to show that the pre-plasma at both the front and rear sides of the target strongly affect the efficiency of the ion acceleration. The mechanism of the plasma flow around mass-limited targets has not yet been identified for laser-driven ion acceleration. Our models indicate that this effect is the cause of the observed limitation to the ion-beam energy in both previous experiments and in our own.

We propose an analytical model that analyzes the divergence of fast ion beams accelerated at the rear of thin foils irradiated with ultra-short intense laser pulses. We demonstrate the critical role played by the non-stationary character of the side components of the electric field, which is responsible for ion acceleration from the back of the foil. The model predictions are in very good agreement with 2D PIC simulations and with the experiments performed in the ultra-high-contrast regime as well.

An analytical distribution function is developed that describes the influence of a light ion component on the explosion of a spherically symmetric, charged cluster composed of two species, when the cluster is irradiated by an ultrashort, intense laser pulse. It is shown that the energy distribution of light ions can be used for diagnostics of the initial density profile of the plasma cluster. The evolution of the energy distribution of light ions is investigated as a function of their number in the cluster. It is possible to create a quasimonoenergetic distribution of the light ions at a specific proportion of the light ions and the degree of ionization of the heavier ion component. Analytical calculations of the explosion of 50 nm water clusters exposed by ultrashort and intense laser pulses are in good agreement with Particle-In-Cell simulations.

The modern state of research on nonlinear optical interaction of high-power laser radiation with plasmas is described in the context of spatial characteristics of radiation. It is shown that SBS and self focusing allow desirable spatial structures of laser pulses to form in plasma© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The unprecedented properties of laser accelerated ion beams result from a highly organized ion emission scenario at the laser-driven source. Multi-channel high resolution ion spectroscopy reveals exact and strong correlation between spectral characteristics and ion trajectories in the beam. These properties are coupled to a well defined ion source evolution as suggested by the experimental data. Such beams are ideal candidates for manipulation with well-established ion beam optics. This is demonstrated with a set of magnetic quadrupole lenses in order to achieve beam collimation and monochromatization.

This paper discusses the width increase of a chirped pulse compressed in an optical compressor when there are various types of mismatches of the components of its diffraction gratings, such as the deviation of the gratings from parallelness and relative rotations and shifts of the grating segments of a composite compressor. Formulas are presented for computing the increment of the dispersion of the group delay and the width increase of the reconstructed pulse, which is associated with the presence of residual angular dispersion, along with formulas for computing the angles of deviation of the diffraction waves for relative rotations of the grating segments and the width increase of the compressed pulse accompanying such rotations. Formulas are obtained for calculating the phase shifts accompanying relative shifts of the grating segments. The question of the diffraction efficiency and the absorption of light energy at the grating surface is considered. The range of groove depths of a sinusoidal grating that makes it possible to maximize the efficiency with the minimum losses of light energy is obtained.

This paper presents the results of studies of the acceleration of macroparticles consisting of fragments of matter from the back side of a solid target when its front surface is irradiated with a picosecond laser pulse with intensity 1013–1015W∕cm2. It is experimentally shown that there are optimal conditions for maximizing the spalling momentum of the target fragments, depending on its thickness and the intensity of the laser pulse on the front surface. The focusing of melted fragments of the substance, split off from the back surface of a target made in the form of a hemisphere, is experimentally demonstrated. The spalling momentum from such a target is greater than the momentum from a flat target of the same thickness by a factor of 6 –7.

Recent investigations of relativistic laser plasmas have shown that the energy transfer from the laser field to the kinetic ion energy and therefore the attainable maximum energy of the ions increases when ultrathin targets are irradiated by laser pulse without prepulse. In this paper, the influence of the target thickness and laser pulse contrast on the energy of the accelerated ions has been studied theoretically as well as experimentally. An optimum target was searched if a real laser pulse with a certain prepulse irradiates the target.

Studies of interaction of a cloud of submicrometer water droplets with ultrashort (40fs) and intense (∼2×1019W∕cm2) laser pulses demonstrate an efficient acceleration of protons and oxygen ions. Due to a high ratio of the volume to the enveloping surface of a single droplet and a large number of droplets in a focal volume, efficient laser pulse absorption is enabled, which provides high electron temperatures and ion acceleration to high energies. The generation of ions with energies more than 1MeV per nucleon is demonstrated. The observed quasi-monoenergetic feature in the proton spectrum is discussed with the thermal expansion–Coulomb explosion model and numerical simulations.

Ion bursts, accelerated by an ultrafast (40 fs) laser-assisted target normal sheath acceleration mechanism, can be adjusted so as to deliver a nearly pure proton beam. Such laser-driven proton bursts have predominantly a low transverse emittance and a broad kinetic spectrum suitable for continuous probing of the temporal evolution of spatially extended electric fields that arise after laser irradiation of thin foils. Fields with a strength of up to 1010 V/m were measured with a new streaklike proton deflectometry setup. The data show the temporal and spatial evolution of electric fields that are due to target charge-up and ion-front expansion following intense laser-target interaction at intensities of 1017-1018 W/cm2. Measurement of the field evolution is important to gain further insight into lateral electron-transport processes and the influence of field dynamics on ion beam properties.

Intense short laser pulses may accelerate ions in thin targets to energies of several MeV per nucleon and highly collimated ion beams may be formed. Quasi-monoenergetic ion beams were generated last year from foils with a specially treated rear surface and from the water droplets. Mass-limited targets such as water μm-sized spheres or small metal discs offer an advantage of reducing the absorbed laser energy spread in the transverse directions. Ion acceleration in targets irradiated by short ultra-intense laser pulses is studied here via two-dimensional in space and three-dimensional in velocities (2D3V) relativistic electromagnetic particle-in-cell code. Simulations were performed for plane and curved foil sections and cylindrical targets that serve as a two-dimensional model of spherical micro-droplets. Two ion species with different charge-to-mass ratios facilitate the formation of persistent peak in energy distribution of the lighter ions, while the heavier ions act like a piston.

Ion acceleration by ultrashort intense femtosecond laser pulses (∼4×1019W∕cm2, ∼30fs) in small targets of uniform chemical composition of two ion species (protons and carbon C4+ ions) is studied theoretically via a particle-in-cell code with two spatial and three velocity components. Energy spectra of accelerated ions, the number and divergence of fast protons, are compared for various target shapes (cylinder, flat foil, curved foil) and density profiles. Dips and peaks are observed in proton energy spectra due to mutual interaction between two ion species. The simulations demonstrate that maximum energy of fast protons depends on the efficiency of laser absorption and the cross section of the hot electron cloud behind the target. A rear-side plasma density ramp can substantially decrease the energy of fast ions and simultaneously enhance their number. These results are compared with analytical estimates and with previously published experiments.

Specific ion spectra have been obtained by irradiating spherical and planar targets with 40fs Ti:Sa laser pulses at intensities of ∼1019W∕cm2. From the mass-limited spherical target, strong modulations in the proton/deuteron spectra and a high laser to ion energy conversion originate, whereas the planar target provides higher cutoff energies of protons. We compare qualitatively models in which the acceleration field is assigned to a multitemperature electron distribution and alternatively where multispecies ion acceleration is important, which both can account for the observed modulations in the spectra. The abundance of ion species and especially the observed strong suppression of the heavy ion species during the ion acceleration from planar targets are estimated on the basis of the interplay of ions with different mass during their ultrafast acceleration and the further ion-bunch propagation.

For measuring the source profile of proton beams, a method using a Thomson mass spectrometer, which has precise energy resolution and enables the discrimination of ion species, was proposed and applied in an experiment with irradiation of 55-fs, 6.6×1018-W∕cm2-laser pulses on a 5-μm-thick copper tape target. The typical measured source size was 150μm at E=400keV and 44μm at E=980keV in full width at half maximum.

It is shown that, when a dielectric coating is deposited, its profile deviates from the initial profile of the metallic grating (

Spectra of intraband absorption of polarized mid-IR light were investigated in undoped, p-, and n-doped InAs/GaAs quantum dots (QDs) covered with an InGaAs layer. Optical matrix elements for intraband electron and hole transitions in QDs have been calculated for different polarizations of light, and a good agreement with the experimental data is obtained. It is shown that the intraband absorption of light by electrons strongly exceeds the absorption by holes. Photoluminescence spectra and TEM images of structures with artificial molecules formed by pairs of QDs were studied.

Arrays of InAs quantum dot (QD) molecules in the GaAs matrix, which consist of pairs of vertically aligned InAs QDs, have been synthesized by molecular beam epitaxy. A study of the resulting structures by transmission electron microscopy demonstrated that the vertically aligned QDs are equal in size. Photoluminescence measurements revealed that the spectra of the samples under study contain bands corresponding to electronic states in QD molecules.