Multi-petawatt Laser Research Articles

Improvement in the temporal contrast in the tens of ps range of the multi-PW Apollon laser front-end.

We demonstrate the impact of the optics roughness in Öffner stretchers used in chirped pulse amplification laser chains and how it is possible to improve the temporal contrast ratio in the temporal range of 10-100 ps by adequately choosing the optical quality of the key components. Experimental demonstration has been realized in the front-end source of the multi-petawatt (PW) laser facility Apollon, resulting in an enhancement of the contrast ratio by two to three orders of magnitude.

Spin-polarized proton beam generation from gas-jet targets by intense laser pulses.

A method of generating spin-polarized proton beams from a gas jet by using a multipetawatt laser is put forward. With currently available techniques of producing prepolarized monatomic gases from photodissociated hydrogen halide molecules and petawatt lasers, proton beams with energy ≳50 MeV and ≈80% polarization are proved to be obtained. Two-stage acceleration and spin dynamics of protons are investigated theoretically and by means of fully self-consistent three-dimensional particle-in-cell simulations. Our results predict the dependence of the beam polarization on the intensity of the driving laser pulse. Generation of bright energetic polarized proton beams would open a domain of polarization studies with laser driven accelerators and have potential application to enable effective detection in explorations of quantum chromodynamics.

Focal-shape effects on the efficiency of the tunnel-ionization probe for extreme laser intensities

We examine the effect of laser focusing on the effectiveness of a recently discussed scheme [M. F. Ciappina et al., Phys. Rev. A 99, 043405 (2019) and M. F. Ciappina and S. V. Popruzhenko, Laser Phys. Lett. 17, 025301 (2020)] for in situ determination of ultrahigh intensities of electromagnetic radiation delivered by multi-petawatt laser facilities. Using two model intensity distributions in the focus of a laser beam, we show how the resulting yields of highly charged ions generated in the process of multiple sequential tunneling of electrons from atoms depend on the shapes of these distributions. Our findings lead to the conclusion that an accurate extraction of the peak laser intensity can be made either in the near-threshold regime, when the production of the highest charge state happens only in a small part of the laser focus close to the point where the intensity is maximal or through the determination of the points where the ion yields of close charges become equal. We show that for realistic parameters of the gas target, the number of ions generated in the central part of the focus in the threshold regime should be sufficient for a reliable measurement with highly sensitive time-of-flight detectors. Although the positions of the intersection points generally depend on the focal shape, they can be used to localize the peak intensity value in certain intervals. Finally, the slope of the intensity-dependent ion yields is shown to be robust with respect to both the focal spot size and the spatial distribution of the laser intensity in the focus. When these slopes can be measured, they will provide the most accurate determination of the peak intensity value within the considered tunnel ionization scheme. In addition to this analysis, we discuss the method in comparison with other recently proposed approaches for direct measurement of extreme laser intensities.

Extremely brilliant GeV γ-rays from a two-stage laser-plasma accelerator.

Recent developments in laser-wakefield accelerators have led to compact ultrashort X/γ-ray sources that can deliver peak brilliance comparable with conventional synchrotron sources. Such sources normally have low efficiencies and are limited to 107-8 photons/shot in the keV to MeV range. We present a novel scheme to efficiently produce collimated ultrabright γ-ray beams with photon energies tunable up to GeV by focusing a multi-petawatt laser pulse into a two-stage wakefield accelerator. This high-intensity laser enables efficient generation of a multi-GeV electron beam with a high density and tens-nC charge in the first stage. Subsequently, both the laser and electron beams enter into a higher-density plasma region in the second stage. Numerical simulations demonstrate that more than 1012 γ-ray photons/shot are produced with energy conversion efficiency above 10% for photons above 1 MeV, and the peak brilliance is above 1026 photons s-1 mm-2 mrad-2 per 0.1% bandwidth at 1 MeV. This offers new opportunities for both fundamental and applied research.

Can Extreme Electromagnetic Fields Accelerate the α Decay of Nuclei?

The possibility to control the α decay channel of atomic nuclei with electromagnetic fields of extreme intensities envisaged for the near future at multipetawatt and exawatt laser facilities is investigated theoretically. Using both analytic arguments based on the Wentzel-Kramers-Brillouin approximation and numerical calculations for the imaginary time method applied in the framework of the α decay precluster model, we show that no experimentally detectable modification of the α decay rate can be observed with super-intense lasers at any so-far-available wavelength. Comparing our predictions with those reported in several recent publications, where a considerable or even giant laser-induced enhancement of the decay rate has been claimed, we identify there the misuse of a standard approximation.

Preplasma effects on laser ion generation from thin foil targets

Under typical experimental conditions related to the interaction of a short pulse laser with a nanometer foil target, the assumption of a target step-function number density profile ceases to be valid due to the existence of a nanosecond long amplified spontaneous emission pedestal prior to the arrival of the main pulse. As a consequence, the formation of a low density extended preplasma should be considered, making the achievement of high ion energy extremely challenging. In this work, a multiparametric study of various preplasma distributions is presented, obtained by combinations of the pedestal intensity, initial foil thickness, and main pulse intensity. Hydrodynamic simulations have been employed to find the target number density distribution prior to the arrival of the main laser pulse. The output of the hydrodynamic simulations is then combined with particle-in-cell simulations, providing a detailed understanding of the complete nanosecond-long laser-foil interaction. Once the laser pulse interacts with the preplasma, it deposits a fraction of its energy on the target, before it is either reflected from the critical density surface or transmitted through an underdense plasma channel. A fraction of hot electrons is ejected from the target, leaving the foil in a net positive potential, which in turn results in proton and heavy ion acceleration. The results of our multiparametric studies are important for forthcoming experiments on the ion acceleration with multipetawatt laser facilities.

Atomic diagnostics of ultrahigh laser intensities

SynopsisWe suggest and discuss a method for precise measurement of ultrahigh laser intensities in the 1020 – 1024W/cm2 range of intensities. The method is based on the observation of multiple sequential tunneling ionization of heavy atoms in the focus of an intense laser beam. It can be of use for probing electromagnetic fields of record power expected to achieve at new multi-petawatt laser facilities.

Multiple colliding laser pulses as a basis for studying high-field high-energy physics

Apart from maximizing the strength of optical electromagnetic fields achievable at high-intensity laser facilities, the collision of several phase-matched laser pulses has been identified theoretically as a trigger of and way to study various phenomena. These range from the basic processes of strong-field quantum electrodynamics to the extraordinary dynamics of the generated electron-positron plasmas. This has paved the way for several experimental proposals aimed at both fundamental studies of matter at extreme conditions and the creation of particle and radiation sources. Because of the unprecedented capabilities of such sources, they have the potential to open up new opportunities for experimental studies in nuclear and quark-gluon physics. We perform here a systematic analysis of different regimes and opportunities achievable with the concept of multiple colliding laser pulses, for both current and upcoming laser facilities. We reveal that several distinct regimes could be within reach of multi-petawatt laser facilities.

Simulating a four-channel coherent beam combination system for femtosecond multi-petawatt lasers.

We simulate a four-channel coherent beam combination (CBC) system designed for femtosecond petawatt lasers. Typical behavior characteristics of the CBC system are revealed. Key parameters relevant to engineering are identified. A simple automatic alignment method is also demonstrated with the virtual CBC system. This work may benefit relevant projects around the world.

Gamma photons and electron-positron pairs from ultra-intense laser-matter interaction: A comparative study of proposed configurations

High-energy γ-photon generation via nonlinear Compton scattering and electron–positron pair creation via the Breit–Wheeler process driven by laser–plasma interaction are modeled, and a number of mechanisms are proposed. Owing to the small cross section, these processes require both an ultra-intense laser field and a relativistic electron bunch. The extreme conditions for such scenarios can be achieved through recent developments in laser technology. Photon emission via nonlinear Thomson and Compton scattering has been observed experimentally. High-energy positron beams generated via a multiphoton process have recently been observed too. This paper reviews the principles of γ-ray emission and e+e− pair creation in the context of laser–plasma interaction. Several proposed experimental setups for γ-ray emission and e+e− pair creation by ultra-intense laser pulses are compared in terms of their efficiency and the quality of the γ-photon and positron beams produced for ultrashort (15 fs) and longer (150 fs) multi-petawatt laser beams.

Extreme brightness laser-based neutron pulses as a pathway for investigating nucleosynthesis in the laboratory

With the much-anticipated multi-petawatt (PW) laser facilities that are coming online, neutron sources with extreme fluxes could soon be in reach. Such sources would rely on spallation by protons accelerated by the high-intensity lasers. These high neutron fluxes would make possible not only direct measurements of neutron capture and β-decay rates related to the r-process of nucleosynthesis of heavy elements, but also such nuclear measurements in a hot plasma environment, which would be beneficial for s-process investigations in astrophysically relevant conditions. This could, in turn, finally allow possible reconciliation of the observed element abundances in stars and those derived from simulations, which at present show large discrepancies. Here, we review a possible pathway to reach unprecedented neutron fluxes using multi-PW lasers, as well as strategies to perform measurements to investigate the r- and s-processes of nucleosynthesis of heavy elements in cold matter, as well as in a hot plasma environment.

Accurate single-shot measurement technique for the spectral distribution of GeV electron beams from a laser wakefield accelerator

We present a technique, based on a dipole magnet spectrometer containing multiple scintillation screens, to accurately characterize the spectral distribution of a GeV electron beam generated by laser wakefield acceleration (LWFA). An optimization algorithm, along with a numerical code, was developed for trajectory tracking and reconstructing the electron beam angle, divergence, and energy spectrum with a single-shot measurement. The code was validated by comparing the results with the Monte-Carlo simulation of electron beam trajectories. We applied the method to analyze data obtained from laser wakefield acceleration experiments performed using a multi-Petawatt laser to accelerate electron beams to multi-GeV energy. Our technique offers a high degree of accuracy to faithfully characterize electron beams with the nonnegligible shot-to-shot beam pointing fluctuations, particularly in the state-of-the-art multi-GeV LWFA experiments performed to push the energy frontier.

Towards ultra-intense ultra-short ion beams driven by a multi-PW laser

AbstractThe multi-petawatt (PW) lasers currently being built in Europe as part of the Extreme Light Infrastructure (ELI) project will be capable of generating femtosecond light pulses of ultra-relativistic intensities (~1023–1024 W/cm2) that have been unattainable so far. Such laser pulses can be used for the production of high-energy ion beams with unique features that could be applied in various fields of scientific and technological research. In this paper, the prospect of producing ultra-intense (intensity ≥1020 W/cm2) ultra-short (pico- or femtosecond) high-energy ion beams using multi-PW lasers is outlined. The results of numerical studies on the acceleration of light (carbon) ions, medium-heavy (copper) ions and super-heavy (lead) ions driven by a femtosecond laser pulse of ultra-relativistic intensity, performed with the use of a multi-dimensional (2D3 V) particle-in-cell code, are presented, and the ion acceleration mechanisms and properties of the generated ion beams are discussed. It is shown that both in the case of light ions and in the case of medium-heavy and super-heavy ions, ultra-intense femtosecond multi-GeV ion beams with a beam intensity much higher (by a factor ~102) and ion pulse durations much shorter (by a factor ~104–105) than achievable presently in conventional radio frequency-driven accelerators can be produced at laser intensities of 1023 W/cm2 predicted for the ELI lasers. Such ion beams can open the door to new areas of research in high-energy density physics, nuclear physics and inertial confinement fusion.

Multi-stage scheme for nonlinear Breit–Wheeler pair-production utilising ultra-intense laser-solid interactions

Multi-petawatt (PW) lasers enable intensities exceeding 1023 W cm−2, at which point quantum electrodynamics (QED) processes, such as electron–positron pair-production via the nonlinear Breit–Wheeler process, will play a significant role in laser-plasma interactions. Using 2D QED-particle-in-cell simulations, we present a two-stage scheme in which nonlinear pair-production is induced via an ultra-intense laser-solid interaction. The first stage is the generation of a γ-ray beam, through the interaction of an ultra-intense laser pulse with a thick target, whose features are found to be strongly dependent on collective plasma effects. This compact, high energy γ-ray beam (characterised by a divergence half-angle ∼10° and average photon energy ∼10 MeV) then interacts with two counter-propagating laser pulses. By varying the laser polarisation and angle of incidence, we show that in the case of two circularly polarised laser pulses propagating at an angle equal to the divergence half-angle of the γ-ray beam, the produced positron distribution is highly anisotropic compared to the case of a standard head-on collision.

Simultaneous polarization transformation and amplification of multi-petawatt laser pulses in magnetized plasmas.

With increasing laser peak power, the generation and manipulation of high-power laser pulses become a growing challenge for conventional solid-state optics due to their limited damage threshold. As a result, plasma-based optical components that can sustain extremely high fields are attracting increasing interest. Here, we propose a type of plasma waveplate based on magneto-optical birefringence under a transverse magnetic field, which can work under extremely high laser power. Importantly, this waveplate can simultaneously alter the polarization state and boost the peak laser power. It is demonstrated numerically that an initially linearly polarized laser pulse with 5 petawatt peak power can be converted into a circularly polarized pulse with a peak power higher than 10 petawatts by such a waveplate with a centimeter-scale diameter. The energy conversion efficiency of the polarization transformation is about 98%. The necessary waveplate thickness is shown to scale inversely with plasma electron density ne and the square of magnetic field B0, and it is about 1 cm for ne = 3 × 1020 cm-3 and B0 = 100 T. The proposed plasma waveplate and other plasma-based optical components can play a critical role for the effective utilization of multi-petawatt laser systems.

Energy absorption in the laser-QED regime

A theoretical and numerical investigation of non-ponderomotive absorption at laser intensities relevant to quantum electrodynamics is presented. It is predicted that there is a regime change in the dependence of fast electron energy on incident laser energy that coincides with the onset of pair production via the Breit-Wheeler process. This prediction is numerically verified via an extensive campaign of QED-inclusive particle-in-cell simulations. The dramatic nature of the power law shift leads to the conclusion that this process is a candidate for an unambiguous signature that future experiments on multi-petawatt laser facilities have truly entered the QED regime.

High power gamma flare generation in multi-petawatt laser interaction with tailored targets

Using quantum electrodynamics particle-in-cell simulations, we optimize the gamma flare (γ-flare) generation scheme from the interaction of a high power petawatt-class laser pulse with a tailored cryogenic hydrogen target having an extended preplasma corona. We show that it is possible to generate an energetic flare of photons with energies in the GeV range and the total flare energy being on a kilojoule level with efficient conversion of the laser pulse energy to γ-photons. We discuss how the target engineering and the laser pulse parameters influence the γ-flare generation efficiency. This type of experimental setup for a laser-based γ-source would be feasible for the upcoming high-power laser facilities. Applications of high intensity γ-ray beams are also discussed.

Broadband main OPCPA amplifier at 808 nm wavelength in high deuterated DKDP crystals.

The optical aperture of ultrashort extreme intensity laser facilities, which reach 10 PW, will be beyond several hundred millimeters. DKDP is by now the only nonlinear crystal that can be grown to such diameter and used in the main optical parametric chirped-pulse amplification (OPCPA) amplifier of such a laser system. Here, at the signal wavelength of 808nm for the first time, we experimentally present a broadband OPCPA system that consists of a pre-amplifier in BBO crystals and a main OPCPA amplifier in two 95% deuterated DKDP crystals. The final amplified spectrum bandwidth exceeds 50nm, and a compressed pulse duration of 27fs has been measured. The conversion efficiency of the main OPCPA amplifier reached 24%, and a net signal gain of 13 was obtained. For the high energy OPCPA amplifier, the influence due to partial absorption on the idler pulses in DKDP crystal is theoretically analyzed. The results indicate the potential utilization of high deuterated DKDP for the main OPCPA amplifiers in a multi-petawatt laser system at 808nm wavelength.

Improvement of focusing performance for a multi-petawatt OPCPA laser facility

In the paper, we demonstrate improvement of the focused intensity for a multi-petawatt optical parametric chirped-pulse amplification laser facility by several methods. An adaptive optics system with a large-size deformable mirror is employed and it applies a closed-loop correction method based on detection of the on-target focal spot rather than wavefront. In addition, a pair of achromatic lenses is designed and utilized to compensate chromatic and spherical aberrations of the laser system. Moreover, the additional dynamic aberrations introduced by 3-stage optical parametric amplifiers are investigated experimentally. After optimization, the focal spot size (full width at half maximum, FWHM) is 3.3 µm × 4.0 µm in x-axis and y-axis directions and the enclosed energy in FWHM is 28% when an on-axis parabolic mirror with a focal length of 800 mm is used. The focused intensity of ~4 × 1021 W cm−2 has been achieved for a 1.6 PW shot. The laser intensity is expected to be 1022 W cm−2 or higher for 4.9 PW peak power.

Relativistic Doppler-boosted \u03b3-rays in High Fields

The relativistic Doppler effect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena. It occurs in the case of a plasma sail accelerated to relativistic velocities by an external driver, such as an ultra-intense laser pulse. Here we show that the relativistic Doppler effect on the high energy synchrotron photon emission (~10 MeV), strongly depends on two intrinsic properties of the plasma (charge state and ion mass) and the transverse extent of the driver. When the moving plasma becomes relativistically transparent to the driver, we show that the γ-ray emission is Doppler-boosted and the angular emission decreases; optimal for the highest charge-to-mass ratio ion species (i.e. a hydrogen plasma). This provides new fundamental insight into the generation of γ-rays in extreme conditions and informs related experiments using multi-petawatt laser facilities.