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Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations. Here, we investigate how to optimize their coupling with solid targets. Experimentally, we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside. The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations, revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection, which is one possible mechanism to boost electron energization. In addition, the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation. Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams. [ABSTRACT FROM AUTHOR]

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing. [ABSTRACT FROM AUTHOR]

Epithermal neutrons from pulsed-spallation sources have revolutionised neutron science allowing scientists to acquire new insight into the structure and properties of matter. Here, we demonstrate that laser driven fast (~MeV) neutrons can be efficiently moderated to epithermal energies with intrinsically short burst durations. In a proof-of-principle experiment using a 100 TW laser, a significant epithermal neutron flux of the order of 105 n/sr/pulse in the energy range of 0.5–300 eV was measured, produced by a compact moderator deployed downstream of the laser-driven fast neutron source. The moderator used in the campaign was specifically designed, by the help of MCNPX simulations, for an efficient and directional moderation of the fast neutron spectrum produced by a laser driven source. [ABSTRACT FROM AUTHOR]

Ion acceleration resulting from the interaction of ultra-high intensity and ultra-high contrast (~10-10) laser pulses with thin Al foil targets at 30° angle of laser incidence is studied. Proton maximum energies of 30 and 18MeV are measured along the target normal rear and front sides, respectively, showing intensity scaling as Ib. For the target front bfront = 0.5-0.6 and for the target rear brear = 0.7-0.8 is observed in the intensity range 1020-1021 W/cm2. The fast scaling from the target rear ~I0.75 can be attributed enhancement of laser energy absorption as already observed at relatively low intensities. The backward acceleration of the front side protons with intensity scaling as ~I0.5 can be attributed to the to the formation of a positively charged cavity at the target front via ponderomotive displacement of the target electrons at the interaction of relativistic intense laser pulses with a solid target. The experimental results are in a good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

The dynamics of self-generated magnetic B-fields produced following the interaction of a high contrast, high intensity (I>1019W cm-2) laser beam with thin (3 μm thick) solid (Al or Au) targets is investigated experimentally and numerically. Two main sources drive the growth of B-fields on the target surfaces. B-fields are first driven by laser-generated hot electron currents that relax over ~10-20 ps. Over longer timescales, the hydrodynamic expansion of the bulk of the target into vacuum also generates B-field induced by non-collinear gradients of density and temperature. The laser irradiation of the target front side strongly localizes the energy deposition at the target front, in contrast to the target rear side, which is heated by fast electrons over a much larger area. This induces an asymmetry in the hydrodynamic expansion between the front and rear target surfaces, and consequently the associated B-fields are found strongly asymmetric. The sole long-lasting (>30 ps) B-fields are the ones growing on the target front surface, where they remain of extremely high strength (~8-10 MG). These B-fields have been recently put by us in practical use for focusing laser-accelerated protons [B. Albertazzi et al., Rev. Sci. Instrum. 86, 043502 (2015)]; here we analyze in detail their dynamics and structure. [ABSTRACT FROM AUTHOR]

The experimental evidence of the correlation between the initial electron density of the plasma and electromagnetic soliton excitation at the wake of an intense (1019 W/cm2) and short (1 ps) laser pulse is presented. The spatial distribution of the solitons, together with their late time evolution into post-solitons, is found to be dependent upon the background plasma parameters, in agreement with published analytical and numerical findings. The measured temporal evolution and electrostatic field distribution of the structures are consistent with their late time evolution and the occurrence of multiple merging of neighboring post-solitons. [ABSTRACT FROM AUTHOR]

Proton radiography using laser-driven sources has been developed as a diagnostic since the beginning of the decade, and applied successfully to a range of experimental situations. Multi-MeV protons driven from thin foils via the Target Normal Sheath Acceleration mechanism, offer, under optimal conditions, the possibility of probing laser-plasma interactions, and detecting electric and magnetic fields as well as plasma density gradients with ∼ps temporal resolution and ∼ 5-10 μm spatial resolution. In view of these advantages, the use of proton radiography as a diagnostic in experiments of relevance to Inertial Confinement Fusion is currently considered in the main fusion laboratories. This paper will discuss recent advances in the application of laser-driven radiography to experiments of relevance to Inertial Confinement Fusion. In particular we will discuss radiography of hohlraum and gasbag targets following the interaction of intense ns pulses. These experiments were carried out at the HELEN laser facility at AWE (UK), and proved the suitability of this diagnostic for studying, with unprecedented detail, laser-plasma interaction mechanisms of high relevance to Inertial Confinement Fusion. Non-linear solitary structures of relevance to space physics, namely phase space electron holes, have also been highlighted by the measurements. These measurements are discussed and compared to existing models. [ABSTRACT FROM AUTHOR]

The direct observation and full characterization of a phase space electron hole (EH) generated during laser-matter interaction is presented. This structure, propagating in a tenuous, nonmagnetized plasma, has been detected via proton radiography during the irradiation with a ns laser pulse (Iλ2≈1014 W/cm2) of a gold hohlraum. This technique has allowed the simultaneous detection of propagation velocity, potential, and electron density spatial profile across the EH with fine spatial and temporal resolution allowing a detailed comparison with theoretical and numerical models. [ABSTRACT FROM AUTHOR]

Through the time- and space-resolved interferometry of a short-pulse low-energy probe beam reflecting on the rear surface of a solid target irradiated on its front surface by a high-intensity laser, we have measured a very abrupt expansion of the target rear surface. The experiments were performed using the LULl 100-TW laser facility with a maximum of 10-20 J energy pulses of > 1019 W · cm-2 intensity, wavelength of 1.053 µm irradiating Al targets. The detected phase changes, with a few micrometers spatial resolution and picosecond temporal resolution, are interpreted as induced by the cloud of fast electrons having propagated through the target and expanding into vacuum. The measurements have been performed using a laser-pulse duration of 320 fs and a laser energy of 20 J, varying the target thickness from 25, 14, and 9.4 µm. The experimental phase measurements are compared to simulations obtained by postprocessing simulation data, run with a 1-D adiabatic plasma-expansion code. The comparison allows one to access, for the first time, to the dynamics of the density and temperature of laser-accelerated fast electrons in solid targets and expanding into vacuum. The same technique also allows one to have information regarding the cold electrons and the energy-partition dynamics. [ABSTRACT FROM AUTHOR]

This paper reviews recent experimental activity in the area of optimization, control, and application of laser-accelerated proton beams, carried out at the Rutherford Appleton Laboratory and the Laboratoire pour l'Utilisation des Lasers Intenses 100 TW facility in France. In particular, experiments have investigated the role of the scale length at the rear of the plasma in reducing target-normal-sheath-acceleration acceleration efficiency. Results match with recent theoretical predictions and provide information in view of the feasibility of proton fast-ignition applications. Experiments aiming to control the divergence of the proton beams have investigated the use of a laser-triggered microlens, which employs, laser-driven transient electric fields in cylindrical geometry, enabling to focus the emitted protons and select monochromatic beamlets out of the broad-spectrum beam. This approach could be advantageous in view of a variety of applications. The use of laser-driven protons as a particle probe for transient field detection has been developed and applied to a number of experimental conditions. Recent work in this area has focused on the detection of large-scale self-generated magnetic fields in laser-produced plasmas and the investigation of fields associated to the propagation of relativistic electron both on the surface and in the bulk of targets irradiated by high-power laser pulses. [ABSTRACT FROM AUTHOR]

A scheme employing an external axial magnetic field is proposed to diagnose the intrinsic divergence of laser-generated fast electron beams, and this is studied numerically with hybrid simulations. The maximum beam radius of fast electrons increases with the initial divergence and decreases with the amplitude of the axial magnetic field. It is indicated that the intrinsic divergence of fast electrons can be inferred from measurements of the beam radius at different depth under the axial field. The proposed scheme here may be useful for future fast ignition experiments and in other applications of laser-generated fast electron beams. [ABSTRACT FROM AUTHOR]

The interaction of an ultraintense laser pulse with a conical target is studied by means of numerical particle-in-cell simulations in the context of fast ignition. The divergence of the fast electron beam generated at the tip of the cone has been shown to be a crucial parameter for the efficient coupling of the ignition laser pulse to the precompressed fusion pellet. In this paper, we demonstrate that a focused hot electron beam is produced at the cone tip, provided that electron currents flowing along the surfaces of the cone sidewalls are efficiently generated. The influence of various interaction parameters over the formation of these wall currents is investigated. It is found that the strength of the electron flows is enhanced for high laser intensities, low density targets, and steep density gradients inside the cone. The hot electron energy distribution obeys a power law for energies of up to a few MeV, with the addition of a high-energy Maxwellian tail. [ABSTRACT FROM AUTHOR]

Multi-Mev proton beams generated by target normal sheath acceleration (TNSA) during the interaction of an ultra intense laser beam (I≥1019 W/cm2) with a thin metallic foil (thickness of the order of a few tens of microns) are particularly suited as a particle probe for laser plasma experiments. The proton imaging technique employs a laser-driven proton beam in a point-projection imaging scheme as a diagnostic tool for the detection of electric fields in such experiments. The proton probing technique has been applied in experiments of relevance to inertial confinement fusion (ICF) such as laser heated gasbags and laser-hohlraum experiments. The data provides direct information on the onset of laser beam filamentation and on the plasma expansion in the hohlraum’s interior, and confirms the suitability and usefulness of this technique as an ICF diagnostic. [ABSTRACT FROM AUTHOR]

When the dominant mechanism for ion acceleration is the laser radiation pressure, the conversion efficiency of the laser energy into the energy of relativistic ions may be very high. Stability analysis of a thin plasma layer accelerated by the radiation pressure shows that Raleigh-Taylor instability may enhance plasma inhomogeneity. In the linear stage of instability, the plasma layer decays into separate bunches, which are accelerated by the radiation pressure similarly to clusters accelerated under the action of an electromagnetic wave. The energy and luminosity of an ion beam accelerated in the radiation-pressure-dominated regime are calculated. [ABSTRACT FROM AUTHOR]

We have compared the acceleration of high-energy ions from the rear surface of thin foils for various prepulse contrast conditions of the ultraintense laser pulse irradiating the targets. The experiments were performed using the Laboratoire pour l'Utilisation des Lasers Intenses 100-TW laser facility with 15-20 J energy pulses of > 1018 W/cm² intensity irradiating aluminum targets of variable thicknesses. The laser pulse contrast ratio ahead of the main pulse (prepulse) was varied using either a fast Pockels cell or a single or double plasma mirror (PM). The latter was installed at an intermediate field position, in between the focusing optics and the target. This way, the effect of reducing the laser prepulse by the PM was optimized. With both methods improving the laser pulse contrast, we have observed that one can significantly reduce the thickness of the target used for proton acceleration and, at the same time, increase 1) the maximum energy of the accelerated protons and 2) the energy conversion efficiency of the process. This offers interesting perspectives from high-energy (5-10 MeV) ion acceleration using sub-petawatt laser facilities. A full characterization of contrast enhancement due to the PM, as well as a detailed analysis of the accelerated proton beams, is presented. [ABSTRACT FROM AUTHOR]

A regime of laser acceleration of protons, which relies on the interaction of ultrahigh contrast laser pulses with ultrathin targets, has been validated using experiments and simulations. Proton beams were accelerated to a maximum energy of ∼7.3 MeV from targets as thin as 30 nm irradiated at 1018 W cm-2 μm2 (1 J, 320 fs) with an estimated peak laser pulse to pedestal intensity contrast ratio of 1011. This represents nearly a tenfold increase in proton energy compared to the highest energies obtainable using non contrast enhanced pulses and thicker targets (>5 μm) at the same intensity. To obtain similar proton energy with thicker targets and the same laser pulse duration, a much higher laser intensity (i.e., above 1019 W cm-2 μm2) is required. The simulations are in close agreement with the experimental results, showing efficient electron heating compared to the case of thicker targets. Rapid target expansion, allowing laser absorption in density gradients, is key to enhanced electron heating and ion acceleration in ultrathin targets. [ABSTRACT FROM AUTHOR]

Very collimated bunches of high energy electrons have been produced by focusing super-intense femtosecond laser pulses in submillimeter under-dense plasmas. The density of the plasma, preformed with the laser exploding-foil technique, was mapped using Nomarski interferometry. The electron beam was fully characterized: up to 10[sup 9] electrons per shot were accelerated, most of which in a beam of aperture below 10[sup -3] sterad, with energies up to 40 MeV. These measurements, which are well modeled by three-dimensional numerical simulations, validate a reliable method to generate ultrashort and ultracollimated electron bunches. [ABSTRACT FROM AUTHOR]

Kα radiation generated by interaction of an ultrashort (1 ps) laser with thin (25 μm) Ti foils at high intensity (2×1016 W/cm2) is analyzed using data from a spherical Bragg crystal imager and a single hit charge-coupled device spectrometer together with Monte Carlo simulations of Kα brightness. Laser to Kα and electron conversion efficiencies have been determined. We have also measured an effective crystal reflectivity of 3.75±2%. Comparison of imager data with data from the relatively broadband single hit spectrometer has revealed a reduction in crystal collection efficiency for high Kα yield. This is attributed to a shift in the K-shell spectrum due to Ti ionization. [ABSTRACT FROM AUTHOR]

Abstract: Laser-driven MeV proton beams are highly suitable for quantitative diagnosis of density profiles in dense matter by employing them as a particle probe in a point-projection imaging scheme. Via differential scattering and stopping, the technique allows to detect density modulations in dense compressed matter with intrinsic high spatial and temporal resolutions. The technique offers a viable alternative/complementary route to more established radiographic methods. A Monte-Carlo simulation package, MPRM, has been developed in order to quantify the density profile of the probed object from the experimentally obtained proton radiographs. A discussion of recent progress in this area is presented on the basis of analysis of experimental data, which has been supported by MPRM simulation. [Copyright &y& Elsevier]

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiment in which such phenomena have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channelling in underdense plasmas have been studied with this technique, as also the process of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. [ABSTRACT FROM AUTHOR]

The acceleration of high-energy ion beams (up to several tens of MeV per nucleon) following the interaction of short (t<1ps) and intense (Iλ2 > 1018W cm-2μm2) laser pulses with solid targets has been one of the most active areas of research in the last few years. The exceptional properties of these beams (high brightness and high spectral cutoff, high directionality and laminarity, short burst duration) distinguish them from those of the lower energy ions accelerated in earlier experiments at moderate laser intensities. In view of these properties, laser-driven ion beams can be employed in a number of groundbreaking applications in the scientific, technological and medical areas. This paper reviews the current state-of-the-art, highlights recent developments and indicate future directions of this research area. [ABSTRACT FROM AUTHOR]

Highly intense bunches of protons and ions with energies of several MeV/u can be generated with ultra-short laser pulses focused on solid targets. In the most common interaction regime, target normal sheath acceleration, the spectra of these particles are spread over a wide range following a Maxwellian distribution. We report on the design and testing of a magnetic chicane for the selection of protons within a limited energy window. This consisted of two successive, anti-parallel dipole fields generated by cost-effective permanent C-magnets with customized configuration and longitudinal positions. The chicane was implemented into the target vessel of a petawatt laser facility with constraints on the direction of the incoming laser beam and guidance of the outgoing particles through a vacuum port. The separation of protons and carbon ions within distinct energy intervals was demonstrated and compared to a ray tracing code. Measurements with radiochromic film stacks indicated the selection of protons within [2.4, 6.9] MeV, [5.0, 8.4] MeV, or ≥6.9 MeV depending on the lateral dispersion. A narrow peak at 4.8 MeV was observed with a time-of-flight detector. [ABSTRACT FROM AUTHOR]

The production of shock- and collimated jet-like features is recorded from the self-emission of a plasma using a 16- frame camera, which can show the progression of the interaction over short (100s ns) durations. A cluster of laser beams, with intensity \(10^{15}\) W/cm \(^{2}\) , was focused onto a planar aluminum foil to produce a plasma that expanded into 0.7 mbar of argon gas. The acquisition of 16 ultrafast images on a single shot allows prompt spatial and temporal characterization of the plasma and enables the velocity of the jet- and shock-like features to be calculated. [ABSTRACT FROM PUBLISHER]

In the past decade, transverse instabilities in the ion acceleration process using the laser radiation pressure method have been a prominent topic of discussion. These instabilities caused by the coupling between quasi-static ions with oscillating electrons through the ponderomotive force lead to the creation of density ripples in the target, ultimately resulting in the breaking of the target. This article investigates the collisional effects on the instability characteristic through theoretical and two-dimensional PIC simulation analysis. In agreement with our simulation studies, theoretical results show that the collision term enhanced the ion acceleration by decreasing the ion density accumulation and temporal growth rate of instability. [ABSTRACT FROM AUTHOR]

Self-focusing of a laser beam is one of the major consequences of nonlinear interaction of laser with plasma. In this paper, self-focusing of skew cosh Gaussian (skew-ChG) laser beam is studied in anisotropic, collisional plasma where in externally exponentially decreasing magnetic field is applied. Skewness parameters in the field profile of skew-ChG laser beam eventually determine intensity profile of the beam. The symmetry in skewness parameter in two transverse directions simplifies the calculations considerably. Second order, nonlinear, ordinary, coupled differential equations for Beam Width Parameters (BWP) are obtained using Akhmanovs approach under Wentzel–Kramers–Brillouin (WKB) and paraxial approximations which are solved numerically. For given amplitude of applied magnetic field, attenuated oscillatory self-focusing is observed with respect to change in attenuation coefficient. [ABSTRACT FROM AUTHOR]

In this paper a simple and novel scheme to develop optical logic gates for fast switching. This can be obtained by sending two laser beams coaxially through nonlinear media with saturating nonlinearity. The nonlinearity in the optical properties on the medium is assumed to be cubic quintic nonlinearity. Semianalytical solutions of the wave equations for the fields of incident laser beams have been obtained by using a variational formalism. Emphasis are put on dynamical variations of beam widths of the laser beams with distance of propagation through the medium. It has been found that the weak beam modulates the intensity variations of the strong beam that giving rise to the possibility of an optical transistor. Combinations of these optical transistors can further be used to obtain logic gates. [ABSTRACT FROM AUTHOR]

Proton bursts with a narrow spectrum at an energy of (2.8 ± 0.3 MeV) are accelerated from sub-micron water spray droplets irradiated by high-intensity (∼5 × 1019 W/cm2), high-contrast (∼1010), ultra-short (40 fs) laser pulses. The acceleration is preferentially in the laser propagation direction. The explosion dynamics is governed by a residual ps-scale laser pulse pedestal which 'mildly' preheats the droplet and changes its density profile before the arrival of the high intensity laser pulse peak. As a result, the energetic electrons extracted from the modified target by the high-intensity part of the laser pulse establish an anisotropic electrostatic field which results in anisotropic Coulomb explosion and proton acceleration predominantly in the forward direction. Hydrodynamic simulations of the target pre-expansion and 3D particle-in-cell simulations of the measured energy and anisotropy of the proton emission have confirmed the proposed acceleration scenario. [ABSTRACT FROM AUTHOR]

The dynamics of electric field generation and radial acceleration of ions by a laser pulse of relativistic intensity propagating in an underdense plasma has been investigated using a one-dimensional electrostatic, ponderomotive model developed to interpret experimental measurements of electric fields (Kar S et al 2007 New J. Phys. 9 402). Ions are spatially focused at the edge of the charge-displacement channel, leading to hydrodynamical breaking, which in turn causes the heating of electrons and an 'echo' effect in the electric field. The onset of complete electron depletion in the central region of the channel leads to a smooth transition to a 'Coulomb explosion' regime and a saturation of ion acceleration. [ABSTRACT FROM AUTHOR]

AbstractThe use of laser-accelerated protons as a particle probe for the detection of electric fields in plasmas has led in recent years to a wealth of novel information regarding the ultrafast plasma dynamics following high intensity laser-matter interactions. The high spatial quality and short duration of these beams have been essential to this purpose. We will discuss some of the most recent results obtained with this diagnostic at the Rutherford Appleton Laboratory (UK) and at LULI - Ecole Polytechnique (France), also applied to conditions of interest to conventional Inertial Confinement Fusion. In particular, the technique has been used to measure electric fields responsible for proton acceleration from solid targets irradiated with ps pulses, magnetic fields formed by ns pulse irradiation of solid targets, and electric fields associated with the ponderomotive channelling of ps laser pulses in under-dense plasmas. [ABSTRACT FROM AUTHOR]

Spectrally-peaked proton beams of high charge (, , nC ) have been observed from the interaction of an intense laser ( W cm−2) with ultrathin CH foils, as measured by spectrally-resolved full beam profiles. These beams are reproducibly generated for foil thicknesses 5–100 nm, and exhibit narrowing divergence with decreasing target thickness down to for 5 nm. Simulations demonstrate that the narrow energy spread feature is a result of buffered acceleration of protons. The radiation pressure at the front of the target results in asymmetric sheath fields which permeate throughout the target, causing preferential forward acceleration. Due to their higher charge-to-mass ratio, the protons outrun a carbon plasma driven in the relativistic transparency regime. [ABSTRACT FROM AUTHOR]

A scheme for electron acceleration by self-focused q-Gaussian laser pulses in under-dense plasma has been presented. The relativistic increase in the mass of plasma electrons gives nonlinear response of plasma to the incident laser pulse resulting in self-focusing. Under the combined effects of the saturation nature of relativistic nonlinearity of plasma, self-focusing and diffraction broadening of the laser pulse, the beam width of the laser pulse evolves in an oscillatory manner. An electron initially on the pulse axis and at the front of the self-focused pulse, gains energy from it until the peak of the pulse is reached. When the electron reaches the tail of the pulse, the pulse begins to diverge. Thus, the deacceleration of the electron from the trailing part of the pulse is less, compared to the acceleration provided by the ascending part of the pulse. Hence, the electron leaves the pulse with net energy gain. The differential equations for the motion of electrons have been solved numerically by incorporating the effect of self-focusing of the laser pulse. [ABSTRACT FROM AUTHOR]

The hydrodynamics of plasma formed in the interaction of 100 ns UV KrF laser pulses with foam targets with volume densities from 5 to 500 mg/cm3 was studied. Initial and dynamic transmittance at 248 nm wavelength were measured. At intensities of about 1012 W/cm2, the propagation rates of radiation through foam targets reached 80 km/s, while plasma stream velocities from both the front and rear sides of targets were approximately the same, ~ 75 km/s, which confirms a volumetric absorption of radiation within the target thickness and the explosive nature of the plasma formation and expansion. [ABSTRACT FROM AUTHOR]

The progressive development of high power lasers over the last several decades enables the study of γ-photon generation when an intense laser beam interacts with matter, mainly via inverse Compton scattering at the high intensity limit. γ-ray flashes are a phenomenon of broad interest, drawing the attention of researchers working in topics ranging from cosmological scales to elementary particle scales. Over the last few years, a plethora of studies predict extremely high laser energy to γ-photon energy conversion using various target and/or laser field configurations. The aim of this article is to discuss several recently proposed γ-ray flash generation schemes, as a guide for upcoming γ-photon related experiments and for further evolution of the presently available theoretical schemes. [ABSTRACT FROM AUTHOR]

Results of numerical simulations for acceleration of proton beams at the irradiation of Al target by a superintense laser pulse are presented. There is a good agreement with the experimental data in a broad range of laser intensities from W/cm to W/cm at the fixed laser pulse duration. The obtained parameters of proton beams were used for calculation of the total yield of particles and neutrons for the nuclear reactions B() and B() C at the collisions of proton beams with boron targets. It is shown that the number of particles escaping boron target and arriving at track detectors is less than 5 of the total amount of particles, because the majority of these particles remain inside the target owing to ionization losses. The derived values of the yield of particles' which arrive at detectors are in good agreement with the experimental data. We also calculate the total yield of neutrons in the reaction B() C. It is found that, at the intensity W/cm of the picosecond laser pulse, the yield is equal to , this value is approximately of 3 of the total yield of particles. [ABSTRACT FROM AUTHOR]

A theoretical investigation of spatiotemporal dynamics of an intense laser pulse with a q-Gaussian spatial irradiance profile interacting with collisionless plasma has been presented. In particular, the dynamics of pulse width and beam widths of the laser pulse have been investigated in detail. Using variational theory, nonlinear partial differential equation governing the evolution of the pulse envelope has been reduced to a set of coupled ordinary differential equations for the pulse width and beam widths of the laser pulse. The differential equations thus obtained have been solved numerically to envision the interplay between self-focusing and self-compression of the laser pulse. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) of elliptical q-Gaussian laser beams interacting with axially inhomogeneous plasmas has been investigated theoretically. An intense laser beam with frequency ω0 propagating through plasma gets coupled with a preexisting electron plasma wave (EPW) at frequency ωep, due to ponderomotive nonlinearity on plasma electrons exerted by the laser beam. This nonlinear interaction of pump beam with EPW produces a back scattered wave at frequency ωs = ω0 − ωep. Using variational theory semi analytical solutions of the coupled nonlinear wave equations for the three waves (pump, EPW and scattered) have been obtained under W.K.B approximation technique. It has been observed that self focusing of the laser beam significantly affects the power of back scattered wave. [ABSTRACT FROM AUTHOR]

This work presents an analytical and numerical study of the relativistic-ponderomotive effect on self-focusing of an intense cosh-Gaussian laser beam in a collisionless magnetized plasma by considering an external magnetic field in the direction of propagation of the laser beam. The nonlinear differential equation for the beam width parameter/intensity of a cosh-Gaussian laser beam in a magnetized plasma is obtained by Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations. The self-focusing of the cosh-Gaussian beam at different values of the magnetic field parameter is investigated. The results have also been compared to relativistic nonlinearity. The results show that the self-focusing effect of cosh-Gaussian beam in magnetized plasma becomes stronger, when relativistic and ponderomotive nonlinearities acts together. In addition, the self-trapping of cosh-Gaussian beam in magnetized plasma has also been studied. Numerical results are presented for the well-established laser and plasma parameters. [ABSTRACT FROM AUTHOR]

Excitation of an electron plasma wave (EPW) by beating two intense q-Gaussian laser beams has been analyzed in thermal quantum plasma. Moment theory in W.K.B approximation has been invoked to find numerical solution of nonlinear Schrodinger equation for Drude model of dielectric function of plasma. The effect of relativistic increase in electron mass on propagation dynamics of laser beams has been incorporated. The laser induced nonlinearity in the dielectric properties of plasma depends not only on the intensity of the first beam but also on that of second beam. Therefore, propagation characteristics of one laser beam affects that of second beam and hence, cross-focusing of the two laser beams takes place. Due to nonuniform intensity distribution along the wavefronts of the laser beams, the background electron concentration gets modified. The amplitude of EPW, that depends on the background electron concentration, thus gets nonlinearly coupled with the laser beams. Numerical simulations have been carried out to investigate the effects of laser-plasma parameters on cross-focusing of the laser beams and further its effect on power of EPW. [ABSTRACT FROM AUTHOR]

Laser plasma acceleration has made remarkable progress in the last few decades, but it also faces many challenges. Although the high gradient is a great potential advantage, the beam quality of the laser accelerator has a certain gap, or it is different from that of traditional accelerators. Therefore, it is important to explore and utilize its own features. In this article, some recent research progress on laser proton acceleration and its irradiation application, which was carried out on the compact laser plasma accelerator (CLAPA) platform at Peking University, have been introduced. By combining a TW laser accelerator and a monoenergetic beamline, proton beams with energies of less than 10 MeV, an energy spread of less than 1%, and with several to tens of pC charge, have been stably produced and transported in CLAPA. The beamline is an object–image point analyzing system, which ensures the transmission efficiency and the energy selection accuracy for proton beams with large initial divergence angle and energy spread. A spread-out Bragg peak (SOBP) is produced with high precision beam control, which preliminarily proved the feasibility of the laser accelerator for radiotherapy. Some application experiments based on laser-accelerated proton beams have also been carried out, such as proton radiograph, preparation of graphene on SiC, ultra-high dose FLASH radiation of cancer cells, and ion-beam trace probes for plasma diagnosis. The above applications take advantage of the unique characteristics of laser-driven protons, such as a micron scale point source, an ultra-short pulse duration, a wide energy spectrum, etc. A new laser-driven proton therapy facility (CLAPA II) is being designed and is under construction at Peking University. The 100 MeV proton beams will be produced via laser–plasma interaction by using a 2-PW laser, which may promote the real-world applications of laser accelerators in malignant tumor treatment soon. [ABSTRACT FROM AUTHOR]

Applicability of J × B mechanism of MeV fast electron generation is clearly demonstrated through observation of directed electron beam along laser propagation direction (simultaneous emission also along laser polarization/transverse directions) in the interaction of ∼25 fs laser pulse with thin foil target at an intensity of 1–7 × 1019 W/cm2. Fast electron temperature is found to be lower (higher) than ponderomotive for shorter (longer) preplasma scale lengths. Role of pre-acceleration of electrons in the rising part of the laser pulse is suggested for observed efficient J × B acceleration for p-polarization case. 2D particle in cell simulation also supports the above-mentioned observations. [ABSTRACT FROM AUTHOR]