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Laser wakefield acceleration (LWFA) continues to grow and awaken interest worldwide, especially as in various applications it approaches performance comparable to classical accelerators. However, numerous challenges still exist until this can be a reality. The complex non-linear nature of the process of interaction between the laser and the induced plasma remains an obstacle to the widespread LWFA use as stable and reliable particle sources. It is commonly accepted that the best wavefront is a perfect Gaussian distribution. However, experimentally, this is not correct and more complicated ones can potentially give better results. in this work, the effects of tuning the laser wavefront via the controlled introduction of aberrations are explored for an LWFA accelerator using the shock injection configuration. Our experiments show the clear unique correlation between the generated beam transverse characteristics and the different input wavefronts. The electron beams stability, acceleration and injection are also significantly different. We found that in our case, the best beams were generated with a specific complex wavefront. A greater understanding of electron generation as function of the laser input is achieved thanks to this method and hopes towards a higher level of control on the electrons beams by LWFA is foreseen. [ABSTRACT FROM AUTHOR]

The amplification in a free-electron laser undulator of a short-wavelength subattosecond pulse formed in a laser plasma upon its interaction with a relativistic electron bunch produced by a petawatt laser is considered. The aim of this work is to find the parameters of the system at which it is possible to amplify ultrashort pulses with a duration of up to hundreds of zeptoseconds. [ABSTRACT FROM AUTHOR]

We present a new phenomenon resulting from the interaction of magnetic beads with cancer cells in a laser trap formed on a slide containing a depression 16.5 mm in diameter and 0.78 mm of maximum depth. This phenomenon includes the apparent formation and expansion of a dark bubble that attracts and incinerates surrounding matter when it explodes, which leads to a plasma emitting intense radiation that has the appearance of a star on a microscopic scale. We have observed the star-like phenomenon for more than 4 years, and the intensity depends on the laser's power. Measuring the laser power of the dark bubble shows the entrapment of electromagnetic energy as it expands. [ABSTRACT FROM AUTHOR]

THz radiation through a novel scheme based on a three-pulse configuration in two-dimensional ordinary and extraordinary modes was investigated. The electromagnetic radiation driven by the linear and nonlinear current density created by the laser-induced plasma mechanism has been evaluated. The numerical findings of the present study show that the electric field of THz radiation is significantly improved compared to the two-color scheme if the third harmonic is included. The asymmetric three-color femtosecond laser fields can be used to control the polarization state, radiation power, and the directivity of the THz radiation. With adjustable time delays between pulses, the polarization controllability of THz radiation from plasma, based on experimental conditions, can be achieved. With this scheme, not only tuning to circularly polarized THz radiation is feasible, but also linear or elliptical polarization can be realized by adjusting time delays. The effects of different laser profiles and wavelengths on ionization rate are considered. Variation of the electric field of the generated THz waves for both ordinary and extraordinary modes of photocurrent mechanism is examined numerically for various spatial laser profiles. The study indicates that a laser pulse profile can be used to control THz radiation. [ABSTRACT FROM AUTHOR]

A novel approach to stabilize the laser's discharge plasma impedance by trigger modulation is presented. The discharge plasma impedance of laser drops due to increased charge carriers during laser operation. The absence of intermittent high voltage discharge pulses provides enhanced time for recombining charge carriers, thus restricting the fall in the laser impedance. It has been observed that by missing 0.1% of discharge pulse, the drop in the laser voltage is improved from 4.3 to 2.3%, and an increase in the laser head current is limited to 3% from 3.6% in 6 h of laser operation. The drop in the optical output power is reduced by 10% at the end of 6 h. Further, the controlled intermittent discharge missing ceases the thermal loading at the cathode fall and lowers the probability of thermal instability in discharge plasma. This will improve the discharge stability and reduces the jitter in the metal vapor laser. We believe this approach of manipulating trigger to attain stable impedance and prevent instability, can be applied to other applications requiring high current large volume stable discharges. [ABSTRACT FROM AUTHOR]

The article presents a physical model of the processes occurring in a nonequilibrium plasma of the working body of metal vapor lasers excited by an inductive pulsed-periodic high-freaquency discharge. The model is based on differential equations of population kinetics, electron energy balance, electric circuit, development of stimulated emission, etc. All equations are adapted to the features of induction discharge and the special geometry of the discharge chamber. A description of the model is presented for a variant of a copper vapor laser with a neon buffer gas. Peculiarities of the dynamics of the parameters of plasma and laser radiation under high-freaquency discharge conditions are noted. [ABSTRACT FROM AUTHOR]

Laser wakefield acceleration (LWFA) of electrons is a highly promising and advanced technique within the field of laser plasma physics, which enables the generation of remarkably high-energy electron beams over a comparatively short distance. In this paper, we have used different Gaussian-like laser pulse profiles of the same amplitude of electric field and laser intensity in magnetized plasma. Generated wakefield and energy gain are calculated analytically by using equation of motion and Maxwell's equation. Our results show that generated wakefield and energy gain are greatly affected by the shape of laser electric field profile. Pulse with broader electric field profile produces more effective LWFA under identical conditions of other parameters. Energy gain by electrons increases slightly with increase in the strength of external magnetic field. Results show that for the broadest laser profile, the magnetic field has more influence on wakefield production and electron energy gain. The role of laser pulse length is also analyzed. In this study, we have obtained a maximum of 151.6 MeV energy gain with experimentally feasible parameters. Our findings will assist researchers in selecting the most energy-efficient pulse profile for LWFA. [ABSTRACT FROM AUTHOR]

The possibility of implementing the relativistic self-trapping of an ultraintense laser pulse in a plasma with an inhomogeneous density profile is proved using the three-dimensional kinetic particle-in-cell simulation. The necessary focusing conditions of laser light are determined depending on the gradient length of the plasma density. The comparison of the efficiency of the laser-induced acceleration of electrons with the case of a homogeneous plasma indicates that the appropriate choice of the position of the focus of laser light and the size of the focusing spot on the density profile ensures the relativistic self-trapping of the laser pulse and its use in innovative applications with the same efficiency as in the case of a homogeneous target. [ABSTRACT FROM AUTHOR]

Interaction of two-color lasers in X-mode and magnetized plasma is investigated. Propagation of lasers perpendicular to the direction of the applied magnetic field in plasma leads to the generation of terahertz waves. A perturbative method is used to solve cold-plasma fluid equations along with electromagnetic wave equations in far-field approximation to characterize the interaction of lasers and magnetized plasma. The analysis leads to the derivation of expressions for the angular and spectral distribution of Terahertz radiation. The effect of plasma density, DC magnetic field, and laser profile on the directionality of THz waves is investigated. Proper selection of laser and plasma parameters leads to the maximization or minimization of radiation power in specific directions. [ABSTRACT FROM AUTHOR]

Experiments were carried out using a tightly focused, prepulse-free KrF laser of 700 fs pulse duration. Harmonics up to 20 eV were generated at an intensity of 1.5×1017 W/cm2 from the plasma on the surface of solid targets. The observation of diffuse harmonics propagation for intensities above 1016 W/cm2 and the fact that polarization of the harmonics appears to be mixed for the highest intensities are attributed to the surface rippling which is an intrinsic consequence of the unstable balance between plasma expansion and light pressure. [ABSTRACT FROM AUTHOR]

The interaction of a noble gas jet (Xe, Kr, He) with a laser plasma at a distance of ∼1 cm from a solid target (Mg, (CH[sub 2])[sub n], LiF, or CF[sub 4]) was studied for the first time. The line spectra that were excited in the course of charge exchange of multicharged ions with noble gas atoms in the interaction region were recorded. A clean (debris-free) soft X-ray source excited by laser pulses focused into a xenon jet was designed and investigated. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Optical and photo-thermal effects have emerged in many fields, including thermal characterization, spectroscopy, transportation, and non-destructive examinations. In this study, the Moore-Gibson-Thompson (MGT) thermoelastic model is used to explore the photo-thermal coupling of an isotropic, homogeneous, semiconducting and thermomagnetic solid. The heat conduction law is modified to include the time derivative of fractional order and theoretically formulate the system of governing equations. Using the extended Mittag–Leffler functions as nonsingular kernels, the Atangana and Baleanu derivatives considers the features of fractional derivatives. As measured by an external reference frame, it is taken into account that the medium rotates with a constant angular velocity about the axis of symmetry. The cavity boundaries undergo thermal shock and time-varying heat flux. It has been shown that the Laplace transform method is a powerful technique for solving such problems that link the plasma and heat transfer with phase delays. It is finally aimed to describe the numerical results for changes in carrier density as a function of time and radial distance, temperature increment, strain, thermal stresses, and displacement using a photo-induced carrier with different values of physical relaxation time and fractional operator. [ABSTRACT FROM AUTHOR]

Laser-wakefield accelerators (LWFAs) driven by widely available 100s TW-class near-infrared laser systems have been shown to produce GeV-level electron beams with 10s–100s pC charge in centimetre-scale plasma. As the strength of the ponderomotive force is proportional to the square of the laser wavelength, more efficient LWFAs could be realised using longer wavelength lasers. Here we present a numerical study showing that 10.6 μ m , sub-picosecond CO2 lasers with peak powers of 100–800 TW can produce high-charge electron beams, exceeding that possible from LWFAs driven by femtosecond near-infrared lasers by up to three orders of magnitude. Depending on the laser and plasma parameters, electron beams with 10s MeV to GeV energy and 1–100 nC charge can be generated in 10–200 mm long plasma or gas media without requiring external guiding. The laser-to-electron energy conversion efficiency can be up to 70% and currents of 100s kA are achievable. A CO2 laser driven LWFA could be useful for applications requiring compact and industrially robust accelerators and radiations sources. [ABSTRACT FROM AUTHOR]

Spectra and structures of near-surface plasma torches were studied experimentally by measuring the specific mass loss and plume luminosity caused by dual-pulse laser radiation at wavelengths 1064 and 532 nm on titanium in air as functions of the time between laser pulses and their sequence. Dependences of the laser-plasma temperature and concentration of charged particles on the paired laser pulse parameters were established at laser radiation power densities q1064 ≤ 3.1·109 and q532 ≤ 2.7·109 W/cm2 for λ = 1064 and 532 nm. The optimal conditions for recording erosion plasma spectra had the initial effect from second-harmonic radiation with a time interval between pulses of 4–5 μs; for specific mass loss, 3–6 μs. The results were important for enhancing the efficiency of laser emission spectral analysis and laser-plasma processing of materials. [ABSTRACT FROM AUTHOR]

New experimental data on the laser irradiation of low-density porous materials in the Mishen facility are presented and discussed. A wide set of optical and X-ray diagnostics was used to analyze the physical processes in porous media with different microstructures and specific densities of 1–30mg/cm[sup 3] exposed to laser pulses with λ = 1.054μm,τ = 3 ns, and I = 10[sup 13]–10[sup 14]W/cm[sup 2]. The features of laser absorption and scattering and the processes of energy transfer in porous media were investigated for different average densities, thicknesses, and microstructures of the targets and different incidence angles of the laser beam. It was found that the material microstructure (chaotic or quasi-ordered) significantly affected the formation and dynamics of a plasma produced inside the irradiated samples that model the components of the advanced targets used in inertial confinement fusion research. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Abstract. The spatial dependence of K[sub alpha] emission generated from laser-produced hot electrons is investigated experimentally and theoretically. In addition, the conversion efficiency of K[sub alpha] production as a function of laser intensity is measured and compared with modeling results. We use the terawatt Ti:sapphire laser at MPQ and vary the peak intensity from 10[sup 15] to 10[sup 18] W/cm[sup 2] with a pulse duration of 200 fs. A solid Cu target is placed at various positions in the laser focus, which allows one to vary the intensity but keep the total energy on the target constant. When the target is near best focus, the FWHM of the K[sub alpha] emission, measured using a knife-edge, is considerably larger than the FWHM of the laser intensity. In measuring the efficiency of K[sub alpha] production using the fundamental wavelength of the laser, a clear maximum of K[sub alpha] emission is observed at a position away from best locus, where the peak intensity is down by more than an order of magnitude from the value at best focus. When the second harmonic of the laser is used, the K[sub alpha] emission is peaked near best focus. The K[sub alpha] emission from layer targets is used to obtain an estimate of the temperature of the hot electrons. Modeling of K[sub alpha] production, using a Monte Carlo electron/photon transport code, shows the relationship between incident electron energy and the emitted K[sub alpha] emission. Efficient K[sub alpha] generation from the low-intensity wings of the laser pulse contributes to the large spot size of the K[sub alpha] emission. The lower electron temperatures that are expected for the second harmonic explain the differences in the location of maximum K[sub alpha] emission for the two wavelengths. We discuss the use of K[sub alpha] emission in photoionizing inner-shell electrons with the goal of achieving X-ray lasing at short wavelengths. [ABSTRACT FROM AUTHOR]

We introduce a new two-step method to fabricate silver-silicon gratings that can excite surface plasmons efficiently. The grating structure was firstly created on a flat silicon substrate by single-pulse nanosecond laser interference lithography. Next, a silver layer of 50 nm was evaporated on the silicon substrate. With proper laser energy, a silver-silicon grating with a period of 1120 nm and depth of 18 nm was successfully fabricated. This grating can produce high-quality surface plasmon resonance (SPR) peaks at various incident angles. Moreover, a SPR sensor was experimentally demonstrated based on the silver-silicon grating, which had high sensitivity of 961.5 nm/RIU and figure of merit of 60. Our method is an efficient way to fabricate periodically nanostructured metals at high speed and low cost. [ABSTRACT FROM AUTHOR]

In this study, a novel method to prepare ZnO nanostructures was proposed by irradiation zinc acetate with nanosecond laser in a liquid medium. Nd-YAG laser was used with energy of 180 mJ and 6000 pulses. As well as, the effects of using various liquids such as ethanol, deionized water, and ethylene glycol on the properties of the prepared ZnO were investigated. Structural, morphological, and optical properties were studied for all samples. Specifically, the X-ray diffractometer results revealed the presence of ZnO with hexagonal crystallization. Most importantly, as indicated by micrographs of scanning electron microscopy, the laser irradiation caused the immediate growth of ZnO nanorods in aqueous solution on the contrary of nanospheres which were grown in the other used solutions. Notably, the optical properties of the prepared ZnO showed that the highest absorption was obtained by ZnO nanospheres. Meanwhile, the energy gap was also studied and found to be between 3.5 and 3.59 eV. The incorporation of all these investigations provides a clear vision for growth mechanisms. This mechanism revealed the one-step growth of ZnO nanostructures with interesting properties that prepared by laser irradiation method. The splendid properties of nanorods structures enhance the photocatalytic performance of ZnO rather than spherical structures. The photocatalyst results revealed that the maximum decomposition of 5 ppm MB by the ZnO nanorods was greater than 98% which achieved after 40 min under UV light irradiation with a fixed catalyst concentration of 12 mg / L. [ABSTRACT FROM AUTHOR]

We have demonstrated proof-of-principle of an incoherent ArF ∗ emission source with a quasi-point emission geometry using a laser-produced plasma in an Ar/F 2/He/Ne mixed gas. The VUV emission characteristics, such as the emission size, were dependent on those of the plasma-initiating laser. The average emission power was 10 μW at a repetition rate of 10 Hz at 193 nm. The average power conversion efficiency of the 193-nm emission from the plasma-initiating Nd:YAG laser was 6.3×10 −6. The average emission power at 193 nm was proportional to that of the plasma-initiating laser, indicating the scaling of the emission source. [ABSTRACT FROM AUTHOR]

We present the results of experiments in which jets are created through the collision of two laser-produced plasmas. These experiments use a simple ‘v-foil’ target design: two thin foils are placed at an angle of 140° to each other, and irradiated with a high-energy laser. The plasmas from the rear face of these foils collide and drive plasma jets moving with a velocity of ∼300 km s−1. By choosing the foil thickness and material to suit the laser conditions available, it has proven possible to create plasma jets for which the relevant scaling parameters show significant overlap with those of outflows associated with young stellar objects (YSOs). Preliminary results are also shown from experiments to study the effect of an ambient gas on jet propagation. Nominally identical experiments are conducted either in vacuum or in an ambient medium of 5 mbar of nitrogen gas. The gas is seen to increase the jet collimation, and to introduce shock structures at the head of the outflow. [ABSTRACT FROM AUTHOR]

A new kind of laser beam named off-axis elliptical flat-topped beam is proposed. This beam is expressed as a finite series of off-axis elliptical Gaussian beams with different beam parameters. Analytical propagation formulas for the off-axis elliptical flat-topped beam through aligned and misaligned optical systems are derived. As a numerical example, the propagation properties of the off-axis elliptical flat-topped beam in free space are calculated and discussed. [ABSTRACT FROM AUTHOR]

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 1014 W/cm2 was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density Ne=(1-1.9)×1021 cm-3 and the electron temperature Te=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 1012 photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period. [ABSTRACT FROM AUTHOR]

An assessment of a novel laser-assisted pulsed plasma thruster (PPT) was conducted, in which a laser-induced plasma was induced through laser-beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration using only a laser beam. It was found that the discharge duration at low-voltage cases was as long as that of laser-induced plasma. However, in high-voltage cases, the discharge duration was much longer than that of laser-induced plasma. In this case, the laser-induced plasma should be leading the main discharge from a capacitor, where a certain amount of neutral components of vaporized propellant must be ionized through the discharge. At 8.65-J discharge energy, the maximum current reached about 8000 A. With a newly developed torsion-balance-type thrust stand, thrust performances of laser-assisted PPTs could be estimated. The impulse bit and the specific impulse linearly increased. On the other hand, the coupling coefficient and the thrust efficiency did not increase linearly. The coupling coefficient decreased with energy showing a maximum value (20.8 µN?s/J) at 0 J, or in a pure laser ablation case. The thrust efficiency first decreased with energy from 0 to 1.4 J and then increased linearly with energy from 1.4 J to 8.6 J. At 8.65-J operation, an impulse bit of 38.1 µN?s, a specific impulse of 3791 s, a thrust efficiency of 8%, and a coupling coefficient of 4.3 µN?s/J were obtained. [ABSTRACT FROM AUTHOR]

Results are presented from experimental studies of pulsed plasma flows generated by nanosecond laser pulses with an intensity of 7 × 108 W/cm2 from a solid-state target in a strong electric field. The current pulses through the laser target and the depth distributions of the iron ions implanted in a silicon substrate to which a negative high-voltage pulse was applied are measured. The physical processes occurring in laser plasma with an initial iron ion density of 6 × 1010 cm–3 are simulated numerically by the particle-in-cell method for different delay times and different shapes of the accelerating high-voltage pulse. The model developed allows one to calculate the ion flows onto the processed substrate, the electron flows onto the target, and the energy spectra of the implanted ions. The results from computer simulations are found to be in good agreement the experimental data. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

We investigate the ablation process in SiO2 by the superposition of 180 fs laser pulse (?center=800 nm) with a 15 ns laser pulse (?center=532 nm). Compared to femtosecond laser pulses alone, we measured an increase of 270±30% in volume of the ejected material with only a total increase of 40% of lasers fluences. This increase of ablation is the result of thermal and incubation effects generated by the femtosecond laser pulse. [ABSTRACT FROM AUTHOR]

Abstract. A femtosecond high-power KrF-laser system was used to create a rapidly ionizing plasma on a BK7 glass slide and the plasma formation was probed by a second laser pulse at 497 nm. During the formation of the plasma the electron density reaches the critical density for 497 nm. Therefore, the reflectivity of the surface rises from a value given by the Fresnel formulas to a value close to 100% and the transmission decreases on the same time scale. It is shown that this method permits a precise timing of two femtosecond laser pulses at different wavelengths. [ABSTRACT FROM AUTHOR]

High-power lasers in the relativistic intensity regime with multi-picosecond pulse durations are available in many laboratories around the world. Laser pulses at these intensities reach giga-bar level radiation pressures, which can push the plasma critical surface where laser light is reflected. This process is referred to as the laser hole boring (HB), which is critical for plasma heating, hence essential for laser-based applications. Here we derive the limit density for HB, which is the maximum plasma density the laser can reach, as a function of laser intensity. The time scale for when the laser pulse reaches the limit density is also derived. These theories are confirmed by a series of particle-in-cell simulations. After reaching the limit density, the plasma starts to blowout back toward the laser, and is accompanied by copious superthermal electrons; therefore, the electron energy can be determined by varying the laser pulse length. [ABSTRACT FROM AUTHOR]

We propose and justify a simple calculation method for (i) evaluating the optimum conditions for the generation of extreme ultraviolet (EUV) emission by a laser plasma source employing a supersonic xenon jet and (ii) finding ways to increase in the efficiency of such sources. The main processes involved in the interaction of laser radiation with a xenon jet target, which account for the EUV emission with a wavelength of 13.5 nm, are taken into account. It is shown that one of the main factors that decreases the output efficiency of such EUV sources is the absorption of generated radiation by the gas target. Qualitative calculations of the optimum conditions for the generation at 13.5 nm have been performed for three lasers with various wavelengths. The most promising results can be expected for a CO2 laser, for which the radiation conversion efficiency on the order of 3% at a xenon pressure of 10–15 Torr can be achieved. [ABSTRACT FROM AUTHOR]

The spectra and dynamics of the line emission of a lead erosion laser plasma at a distance of 1 mm from the target are investigated. The plasma is ignited in a vacuum (P = 3–12 Pa) with a pulse-periodic neodymium laser (τ = 20 ns, f = 12 Hz, W = (1–2) × 10[sup 9] W/cm[sup 2] , and λ = 1.06 μm). The data obtained are used to analyze the emission dynamics and the mechanism of formation of the laser plume. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A long-pulse-width high-output energy (120 ns FWHM, 7 J) XeCl laser has been focused on thin tape targets (Cu and Ta) to generate more than 100-ns-long (FWHM) EUV pulses in the 10-30 nm spectral region, suitable for projection microlithography. The conversion efficiency was more than 20% over a 2π solid angle. We observed debris emission using a gated CCD camera, and measured the debris speed for different irradiation conditions. We found irradiation conditions such that the measured velocities were low enough that simple mechanical devices combined with krypton at low-pressure could efficiently stop both ionic debris and cluster debris. Our results show that a suitable combination of driving-laser characteristics, target material and thickness, environment gas and mechanical choppers can make clean and increase the power of EUV solid-target laser-plasma sources. [ABSTRACT FROM AUTHOR]

One of the problems when increasing the intensity of a femtosecond laser pulse is the propagation of the beam. As the intensity increases nonlinear effects begin to play a significant role. When arriving to the terawatt domain, nonlinear effects and filamentation give rise to a new phenomenology in the propagation. The aim of this paper is to analyze new possibilities to control the beam shape to Taylor the interaction of the beam with the target at large distances. [ABSTRACT FROM AUTHOR]

Results of an experiment on the interaction of laser-produced plasma with a pulsed gas jet are reported. A resonant charge-exchange pumping of the n=3 level of the C3+ ion was observed. A spatial structure of the region of intensive interaction was obtained by a short time imaging of filtered plasma radiation. According to independent probe measurements, the interaction was realized at densities of ions and gas particles in excess of 1016 cm-3. The obtained data provide a prospect for future experiments on laser gain in the EUV spectral range based on charge-exchange pumping of the C5+ ion. [ABSTRACT FROM AUTHOR]

We report the generation of diffraction patterns using X-ray pulses from a fs-laser plasma focused by an X-ray capillary lens to a spot size smaller than 100 μm. A thin moving iron tape is irradiated at 10 Hz with 200 mJ/130 fs titanium–sapphire laser pulses. [ Fe]Kα (λ=0.194 nm) radiation emitted from the rear side of the tape is focused to a spot by the capillary lens resulting in an intensity enhancement of about 1600. The ability of this system to effectively allow diffraction from samples of micron size is demonstrated by producing well-illuminated diffractograms from a Si(111) crystal with good signal to noise ratio obtained in only about 10 s. The different path lengths of propagation in the lens induce an angle-encoded delay of the converging X-ray pulse and thus provide the possibility of realizing a novel ultra-fast streak camera. [ABSTRACT FROM AUTHOR]

For the interpretation of experiments for acceleration of electrons at interaction up to nearly GeV energy in laser produced plasmas, we present a new model using interaction magnetic fields. In addition to the ponderomotive acceleration of highly relativistic electrons at the interaction of very short and very intense laser pulses, a further acceleration is derived from the interaction of these electron beams with the spontaneous magnetic fields of about 100 MG. This additional acceleration is the result of a laser-magnetic resonance acceleration (LMRA) around the peak of the azimuthal magnetic field. This causes the electrons to gain energy within a laser period. Using a Gaussian laser pulse, the LMRA acceleration of the electrons depends on the laser polarization. Since this is in the resonance regime, the strong magnetic fields affect the electron acceleration considerably. The mechanism results in good collimated high energetic electrons propagating along the center axis of the laser beam as has been observed by experiments and is reproduced by our numerical simulations. [ABSTRACT FROM AUTHOR]

Ultrashort high-energy electron beams are generated by focusing fs Ti:sapphire laser pulses on a thin metal tape at normal incidence. At laser intensities above 1016 W/cm2 , the fs laser plasma ejects copious amounts of electrons in a direction parallel to the target surface. These electrons are directly detected by means of a backside illuminated X-ray CCD, and their energy spectrum is determined with an electrostatic analyzer. The electrons were observed for two laser polarization directions, parallel and perpendicular to the observation direction. At the maximum applied intensity of 2×1017 W/cm2, the energy distribution peaks at around 35 keV with a hot tail detectable up to about 300 keV. The number of electrons per shot at 35 keV is about 5×108 per sterad per keV. Quasi-monoenergetic electron pulses with a relative energy spread of 1% were produced by using a 50-µm slit in the beam path after the analyzer. This approach offers great potential for time-resolved studies of plasma, liquid, and surface structures with atomic-scale spatial resolution. [ABSTRACT FROM AUTHOR]

Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV?m-1 (refs 1-3). These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators as compact next-generation sources of energetic electrons and radiation. To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse. The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread, which limits potential applications. Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 109 electrons above 80?MeV). Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance. The results open the way for compact and tunable high-brightness sources of electrons and radiation. [ABSTRACT FROM AUTHOR]

The results of measurements of the spectral and temporal parameters of the 3ω[sub 0]/2-harmonic emission in experiments on irradiating burning-through thin foils by laser pulses with intensities of ∼10[sup 14 ]W/cm[sup 2] are presented and analyzed. The time-dependent scale length of the plasma density and the temperature at a level of one-fourth the critical density are estimated from the measured splitting between the spectral components and the measured ratio of their intensities by using a simplified model that takes into account the detailed mechanism for 3ω[sub 0]/2-harmonic generation. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The formation of craters in targets of various materials under the action of a high-power neodymium-laser pulse at radiation intensities from 10[sup 10] to 10[sup 14]W/cm[sup 2] was studied experimentally and theoretically. The interaction between the laser beam and solid targets is investigated to determine the efficiency of the ablation loading of various materials and the transformation of the laser energy into the energy of a shock wave. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The crater formation process is studied in the "laser - Al solid target" interactions on the PALS iodine laser facility. A great variety of laser beam parameters are used to irradiate massive aluminum targets. Large laser energies available (up to 600 J) open a possibility to investigate the process of crater formation for physical conditions different from the earlier studies for the lower laser energies. Comparison with the earlier results is presented. A simple theory, LSM (laser simulation method), has been applied for the analysis of the experimental results. This model leads to a universal relation (scaling law) for the crater relative volume. Our work extends the study of crater formation to the "virtual" macroparticle velocities exceeding 100 km/s. The scaling law is derived here for this previously unexplored region. An alternative method of studying crater formation is also proposed. [ABSTRACT FROM AUTHOR]

A defect–deformation (DD) model of irregular rough microstructure formation on the surface of semiconductors and metals under laser irradiation is developed. The DD model describes the development of roughness on various (from micron to nanometer) scales and agrees with the experimental data on the relationships between the surface roughness scale and the parameters of laser radiation and processed materials. Possibilities of controlled modification of the characteristics of laser-induced roughness by means of external actions are considered. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

An efficient diode-pumped passively Q-switched Nd:GdVO4/Cr4+:YAG laser was employed to generate a high-repetition-rate, high-peak-power eye-safe laser beam with an intracavity optical parametric oscillator (OPO) based on a KTP crystal. The conversion efficiency for the average power is 8.3% from pump diode input to OPO signal output and the slope efficiency is up to 10%. At an incident pump power of 14.5 W, the compact intracavity OPO cavity, operating at 46 kHz, produces average powers at 1571 nm up to 1.2 W with a pulse width as short as 700 ps. [ABSTRACT FROM AUTHOR]

Reports that high acceleration rates and the production of well-populated, high-quality beams, signal the potential of electron accelerators which make electrons surf a laser-driven plasma wave. Generation of waves in a plasma using short laser pulses; Observation that particles have been accelerated in wakefields at rates that are more than a thousand times higher than those achieved by accelerators based on conventional large-scale technology.

We present the set-up and the results of a supercritical radiative shock experiment performed with the LULI nanosecond laser facility. Using specific designed targets filled with xenon gaz at low pressure, the propagation of a strong shock with a radiative precursor is evidenced. The main measured quantities related to the shock (electronic density, propagation velocities, temperature, radial dimension) are presented and compared with various numerical simulations. [ABSTRACT FROM AUTHOR]

The wavelength conversion of femtosecond laser pulses in laser plasmas containing clusters of different nature and dimension (fullerenes, metal nanoparticles) is studied. Pulses of a titanium-sapphire laser are used in combination with orthogonally polarized second-harmonic pulses as radiation to be converted. Variations in the generation efficiency of higher harmonics are analyzed under conditions of phase-modulated pulses. It is shown that the optimization of components of a nonlinear optical plasma medium, of plasma excitation conditions by single- and two-color pumps, and of phase and spectral parameters of radiation to be converted leads to a considerable increase in the generation efficiency of higher harmonics. [ABSTRACT FROM AUTHOR]

Abstract. X-ray emission from a double-stream gas puff target irradiated with a nanosecond Nd:glass laser pulse was studied for the first time. The target was formed by pulsed injection of a high-density gas into a gas cloud by using the double-nozzle setup. This new concept allows a high-density gaseous target to be formed at a relatively large distance from the nozzle output. Enhanced X-ray emission in the 1-keV energy range and a smaller source size were observed as compared to the ordinary gas puff target created by pulsed injection of gas into vacuum. This new approach should be useful in the development of a laser-produced X-ray source for various applications. [ABSTRACT FROM AUTHOR]

Intense laser fields interact very differently with micrometric rough surfaces than with flat objects. The interaction features high laser energy absorption and increased emission of MeV electrons, ions, and of hard x-rays. In this work, we irradiated isolated, translationally-symmetric objects in the form of micrometric Au bars. The interaction resulted in the emission of two forward-directed electron jets having a small opening angle, a narrow energy spread in the MeV range, and a positive angle to energy correlation. Our numerical simulations show that following ionization, those electrons that are pulled into vacuum near the object's edge, remain in-phase with the laser pulse for long enough so that the Lorentz force they experience drive them around the object's edge. After these electrons pass the object, they form attosecond duration bunches and interact with the laser field over large distances in vacuum in confined volumes that trap and accelerate them within a narrow range of momentum. The selectivity in energy of the interaction, its directionality, and the preservation of the attosecond duration of the electron bunches over large distances, offer new means for designing future laser-based light sources. [ABSTRACT FROM AUTHOR]

An Omega-like beam configuration is considered where the 60-beam layout can be separated into two independent sub-configurations with 24 and 36 laser beams, each minimizing direct drive illumination non-uniformity. Two different laser focal spot profiles, one associated with each configuration, are proposed to apply the zooming technique in order to increase the laser-target coupling efficiency. This approach is used by 1D hydrodynamics simulations of the implosion of a direct-drive capsule characterized by a relatively large aspect ratio A = 7 and an optimized laser pulse shape delivering a maximum of 30 TW and 30 kJ, with different temporal pulse shapes in each of the two sets of beams. It is shown that zooming allows for an optimistic 1D thermonuclear energy gain greater than one while without zooming the thermonuclear gain remains largely below one. While this is incompatible with the as-built Omega laser, it provides a promising option for a future intermediate-energy direct drive laser system. [ABSTRACT FROM AUTHOR]

This paper mainly discusses the current research status and development trend of on-line monitoring technology for laser additive manufacturing. We have analyzed various on-line monitoring techniques for laser additive manufacturing based on visual imaging, temperature field, spectral analysis, and acoustic principles. Numerous analyses are performed on the monitored objects, the melt pool, including melt pool temperature and morphology dimensions, and the formed parts, including microstructure and properties. The analysis of on-line monitoring techniques for laser additive manufacturing is expected to find the research directions that meet future development trends. [ABSTRACT FROM AUTHOR]

One of the remarkable phenomena in the laser-matter interaction is the extremely efficient energy transfer to γ -photons, that appears as a collimated γ -ray beam. For interactions of realistic laser pulses with matter, existence of an amplified spontaneous emission pedestal plays a crucial role, since it hits the target prior to the main pulse arrival, leading to a cloud of preplasma and drilling a narrow channel inside the target. These effects significantly alter the process of γ -photon generation. Here, we study this process by importing the outcome of magnetohydrodynamic simulations of the pedestal-target interaction into particle-in-cell simulations for describing the γ -photon generation. It is seen that target tailoring prior the laser-target interaction plays an important positive role, enhancing the efficiency of laser pulse coupling with the target, and generating high energy electron-positron pairs. It is expected that such a γ -photon source will be actively used in various applications in nuclear photonics, material science and astrophysical processes modelling. [ABSTRACT FROM AUTHOR]

The collision of plasma fronts upon laser breakdown in atmosphere under normal conditions has been studied. This interaction leads to an increase in the integral luminosity (which can be 85% higher than that for the noninteracting plasmas, depending on the regime of motion of the colliding plasma fronts) and in the intensity of emission lines on the background of continuous emission from laser plasma. [ABSTRACT FROM AUTHOR]