High-intensity Short-pulse Laser Research Articles

Dynamic flyer in barrel imaging via high intensity short-pulse laser.

The thin flyer is a small-scale flying object, which is well known as the core functional element of the initiator. Understanding how flyers perform has been a long-standing issue in detonator science. However, it remains a significant challenge to explore how the flyer is formed and functions in the barrel of the initiator via tabletop devices. In this study, we present dynamic and unprecedented images of flyer in barrel via high intensity short-pulse laser. Advanced radiography, coupled with a high-intensity picosecond laser X-ray source, has enabled the provision of state-of-the-art radiographs in a single-shot experiment for observing micron-scale flyer formation in a hollow cylinder in nanoseconds. The flyer was clearly visible in the barrel and was accelerated and restricted differently from that without the barrel. This first implementation of a tabletop X-ray source provided a new approach for capturing dynamic photographs of small-scale flying objects, which were previously reported to be accessible only via an X-ray phase-contrast imaging system at the advanced photon source. These efforts have led to a significant improvement of radiographic capability and a greater understanding of the mechanisms of "burst" of exploding foil initiators for this application.

Topological structure effects of Laguerre-Gaussian laser on self-collimation acceleration mechanism

Energetic plasma beams can be generated through the interaction between a short-pulse high-intensity laser and solid target. However, obtaining collimated plasma beams with low divergence remains challenging. In this study, we devised a self-collimation scheme driven by a topologically structured Laguerre–Gaussian (LG) laser that irradiates a thin target in three-dimensional particle-in-cell simulations. It was observed that a high-density and narrow plasma beam could be formed by the intrinsic hollow intensity distribution of the LG laser. A magnetic tunnel was generated around the beam and collimated the plasma beam within a radius of hundreds of nanometers. This collimation can be enhanced by increasing the topological charge from l = 1 to l = 3 and then destroyed for a larger l. The collimation method is promising in applications requiring well-collimated energetic plasma beams, such as indirect drive inertial con-finement fusion, laboratory astrophysics, and radiation therapy.

Shock Waves in Weakly Relativistic e-p-i Plasma: Application to Plasma Created by Ultraintense Short Pulse Laser

In this article, the role of the positrons shock waves generation in weakly relativistic laser-created plasma is investigated. The plasma considered is generated on the rear face of a target, irradiated by a high intensity short pulse laser, in the framework of target normal sheath acceleration (TNSA) mechanism. This plasma is composed of Boltzmann distributed positrons, hot and cold super-thermal electrons, and dynamic ions. Kinematic viscosity among the plasma constituents has been also considered. With the purpose of studying the behavior of nonlinear ion acoustic shock waves (IASHWs), the reductive perturbation method (RPM) has been employed and Korteweg-de Vries Burgers equation has been derived. It was observed that different plasma parameters (namely, electrons super-thermality, number of positrons, ion temperature, kinematic viscosity, etc.) have a real impact on the propagation of IASHWs. As electron–positron plasmas with ion possessing relativistic velocities are often detected in laboratory experiments, astrophysical, and space environments, the present work will help to explain the different types of collective processes and instabilities in regions where e-p-i plasmas can exist.

Experimental verification of TNSA protons and deuterons in the multi-picosecond moderate intensity regime

Ion acceleration from high intensity short pulse laser interactions is of great interest due to a number of applications, and there has been significant work carried out with laser energies up to a few 100 J with 10's of femtosecond to 1 ps pulse durations. Here, we report results from an experiment at the OMEGA EP laser, where laser energy and pulse length were varied from 100 to 1250 J and 0.7–30 ps, respectively, in the moderate (2×1017–2×1018 W/cm2) laser intensity regime. Ions and electrons were simultaneously measured from disk targets made of CH and CD by a Thomson parabola and a magnetic spectrometer, respectively. Measurements showed that the electron temperature, Te (MeV), has a dependence on the laser energy, EL (J), and pulse duration, τL (ps), and its empirical scaling was found to be 0.015×EL0.90τL−0.48. The maximum proton and deuteron energies are linearly dependent on the electron temperature, (5.60 ± 0.26)×Te and (3.17 ± 0.18)×Te, respectively. A significant increase in proton numbers with the laser energy was also observed. The increase in the maximum proton energy and proton count with higher energy longer duration pulses presented in this article shows that such laser conditions have a great advantage for applications, such as the proton radiograph, in the moderate laser intensity regime.

Two-dimensional parametric design of short pulse laser driven iron opacity experiments

High intensity short pulse lasers are commonly used to create high temperature and high density plasmas. These plasmas are used to study fundamental properties such as the equation of state and opacity. The targets often use small-diameter, thin buried layers of the materials of interest, surrounded by a tamper of low atomic number material such as plastic. Computational modeling is used to design and interpret experiments with short pulse lasers. Most of the modeling to date has assumed one-dimensional plane-parallel geometry. In this paper, the effects of radial gradients in the irradiation of thin planar targets are studied with one- and two-dimensional radiation/hydrodynamic simulations. It is found that the main effect of radial gradients is the averaging of plasma conditions and x-ray emission over the pattern of irradiation. Differences between one- and two-dimensional simulations arise because the plasma conditions and x-ray emission are, in general, nonlinear functions of the temperature of the plasma and thereby also nonlinear functions of the irradiation intensity. The differences increase with the ratio of the buried layer radius to the laser spot radius. The root mean square difference in the inferred iron L-shell opacity is less than 30% when the ratio is less than 1.0 and about 70% when the ratio is 1.5.

Accelerating the rate of discovery: toward high-repetition-rate HED science

As high-intensity short-pulse lasers that can operate at high-repetition-rate (HRR) (>10 Hz) come online around the world, the high energy density (HED) science they enable will experience a radical paradigm shift. The >103 increase in shot rate over today’s shot-per-hour drivers translates into dramatically faster data acquisition, more experiments, and the ability to exploit machine learning, and thus the potential to significantly accelerate the advancement of HED science. A wide range of HED experiments, from opacity investigations to secondary source generation to plasma nuclear physics, will benefit from the increased statistics, precision, and exploration of phase space. Besides increasing the rate at which scientific experiments can be performed, HRR also allows for the rapid delivery of optimal experiments supported by simulations and modeling augmented by close coupling to empirical data. To fully realize such an HRR framework, numerous subsystems must be developed and brought together, including feedback laser control loops, high-throughput targetry and diagnostics, cognitive simulation, enhanced HED codes, and advanced data analytics. This paper describes the vision for an integrated HRR laser experimental HED system and outlines some of the major considerations and challenges for realizing it.

Optimized window to produce ultra-intense and ultra-compressed laser pulses by Stimulated Brillouin Scattering

We propose a theoretical model to produce ultra-intense and ultra-compressed laser pulses based on Stimulated Brillouin Scattering (SBS) process. The amplification of laser pulses via Brillouin amplification process is obtained when three waves (two transverse electromagnetic waves and a longitudinal plasma wave) couple in the plasma when resonance condition for energy (frequency ω) and momentum (wave-vector k) is satisfied. Counter propagating seed pulse takes energy from laser pulse when they interact with each other via the process of stimulated Brillouin scattering and finally it gets amplified and compressed. We optimize the parameters (like initial plasma density, initial laser pulse intensity, interaction time, wave breaking time, fillamentation time etc.) for SBS compression and amplification to obtain high intensity laser pulse. This optimized window exactly match with the simulation results reported by Weber et al. [1]. Due to strong SBS within the optimum parametric window, one can develop compact plasma-based amplifier, which can produce high intensity short laser pulse. This technique offers damage less amplification of laser pulses. The amplification and compression ratio obtained in this model are 94 and 30, respectively. These intensities can be used as seed intensities to obtain Zetta watt laser pulses using C-3 (Cascade, Conversion and Compression) technique reported by Mourou et al. [2].

Order-of-magnitude increase in laser-target coupling at near-relativistic intensities using compound parabolic concentrators

Achieving a high conversion efficiency into relativistic electrons is central to short-pulse laser application and fundamentally relies on creating interaction regions with intensities ≫10^{18}W/cm^{2}. Small focal length optics are typically employed to achieve this goal; however, this solution is impractical for large kJ-class systems that are constrained by facility geometry, debris concerns, and component costs. We fielded target-mounted compound parabolic concentrators to overcome these limitations and achieved nearly an order-of-magnitude increase to the conversion efficiency and more than tripled electron temperature compared to flat targets. Particle-in-cell simulations demonstrate that plasma confinement within the cone and formation of turbulent laser fields that develop from cone wall reflections are responsible for the improved laser-to-target coupling. These passive target components can be used to improve the coupling efficiency for all high-intensity short-pulse laser applications, particularly at large facilities with long focal length optics.

Quasi mono-energetic heavy ion acceleration from layered targets

In the present work, we demonstrate acceleration of quasi monoenergetic heavy ions during the interaction of a high-intensity short-pulse laser with multi-layer targets. The targets, consisting of layers of high-Z (gold) and low-Z (carbon) species a few nm thick, have been used to tailor the energy spectra of the high-Z ion species. Au-ion bunches of energy around 500 keV with an energy spread of less than 20% are observed. Particle-in-cell simulations provide explanation for a number of features of the experimental observations. Several behaviors, in addition to the expected sheath-field acceleration, were found to be involved. It is found that the Au layer is pistoned outward by the underlying Si substrate whilst simultaneously being tamped at its leading edge by the carbon overlay. The simulations show best agreement with the experiments when the carbon layer is first rarefied by the laser prepulse. In these cases, the simulations reproduce the double-humped spectra found in the experiment. Ion-electrostatic instabilities rapidly lead to the formation of a single trapping-like structure in phase space of relatively long wavelength. This long-lived structure dominates the ion acceleration and produces a double-peaked energy spectrum. It is suggested that the instability responsible may be of the Pierce-type.

ReLaX: the Helmholtz International Beamline for Extreme Fields high-intensity short-pulse laser driver for relativistic laser–matter interaction and strong-field science using the high energy density instrument at the European X-ray free electron laser facility

Abstract High-energy and high-intensity lasers are essential for pushing the boundaries of science. Their development has allowed leaps forward in basic research areas, including laser–plasma interaction, high-energy density science, metrology, biology and medical technology. The Helmholtz International Beamline for Extreme Fields user consortium contributes and operates two high-peak-power optical lasers using the high energy density instrument at the European X-ray free electron laser (EuXFEL) facility. These lasers will be used to generate transient extreme states of density and temperature to be probed by the X-ray beam. This paper introduces the ReLaX laser, a short-pulse high-intensity Ti:Sa laser system, and discusses its characteristics as available for user experiments. It will also present the first experimental commissioning results validating its successful integration into the EuXFEL infrastructure and viability as a relativistic-intensity laser driver.

Development of a Platform at the Matter in Extreme Conditions End Station for Characterization of Matter Heated by Intense Laser-Accelerated Protons

High-intensity short-pulse lasers have made possible the generation of energetic proton beams, unlocking numerous applications in high energy density science. One such application is uniform and isochoric heating of materials to the warm dense matter (WDM) state. We have developed a new experimental platform to simultaneously create and probe WDM at the matter in extreme conditions (MEC) end station at the Linac Coherent Light Source (LCLS). The short pulse optical laser (delivering up to 1 J in 45 fs) and the ultrabright LCLS X-ray laser with tunable frequency, respectively, deliver high power required to heat materials to WDM and precision-timed high-resolution X-rays to probe them. The laser-accelerated proton beam driven from a flat 1.5- $\mu \text{m}$ Cu foil was first measured then directed to a secondary sample of Al or polypropylene (PP), typically 300– $400~\mu \text{m}$ away. The time evolution of the sample electron temperature was measured using streaked optical pyrometry, where we observed a peak temperature of 0.9 ± 0.15 eV on the rear surface of an Al sample heated by the proton beam. Simulations using the hybrid-PIC code LSP and the rad-hydro code HELIOS show that a measured proton beam can heat Al to approximately 4 eV and PP to 1 eV if instead focused by a hemispherical Cu target. Through additional LSP simulations, we anticipate creating hotter WDM states (~20 eV) by increasing the laser energy to 10 J and keeping the other laser parameters fixed.

Effect of optical field ionisation on the generation of wake fields by femtosecond laser pulses in an inhomogeneous plasma

We consider the interaction of a high-intensity short laser pulse with an argon gas during optical field ionisation. Modelling in a three-dimensional cylindrical symmetric geometry is performed at various moderately relativistic intensities and positions of the focal plane of the laser beam in the case of both optical gas ionisation and a pre-ionised plasma. The influence of the processes occurring during optical field ionisation of the gas on the generation of wake waves is investigated, and the conditions are found under which intense wake fields are produced in a plasma formed from an inhomogeneous argon gas jet. The possibility of using a gas with a large number of electrons on the outer shell (argon) to excite intense wake waves and accelerate electrons is demonstrated. Despite significant ionisation refraction of the laser pulse on a radially inhomogeneous density profile of plasma electrons formed during optical field ionisation, the region of the parameters of the laser pulse and the gas target is determined at which ionisation refraction leads to the excitation of an intense wake wave. It is found that in a pre-ionised plasma a wake wave is not generated even at the same laser radiation intensity.

Flash X-ray backlight technique using a Fresnel phase zone plate for measuring interfacial instability

Interfacial instabilities in high-energy-density plasmas are important topics in various research fields such as inertial confinement fusion, planetary sciences, and astrophysics. The growth of the instabilities can be examined in the laboratory by using high-power lasers coupled with high-resolution imaging technique. The resolutions both in space and time are essential for the observation of tiny and transient phenomena in high-energy-density plasmas. Here, the growth of a sinusoidal corrugation on the surface of a polystyrene foil during the laser-driven Richtmyer-Meshkov instability was measured by high-resolution X-ray shadowgraphy. In our experiment, a high-intensity short-pulse laser produced the X-ray flash that ensures a better temporal resolution. A Fresnel Phase Zone Plate was used for the improvement of spatial resolution, which realized an accuracy of 5.0 ± 1.0 µm in our system.

Plasma mirror focal spot quality for glass and aluminum mirrors for laser pulses up to 20 ps.

High-intensity short-pulse lasers are being pushed further as applications continue to demand higher laser intensities. Uses such as radiography and laser-driven particle acceleration require these higher intensities to produce the necessary x-ray and particle fluxes. Achieving these intensities, however, is limited by the damage threshold of costly optics and the complexity of target chambers. This is evidenced by the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory, producing four high-energy $ \approx 1\;{\rm kJ} $≈1kJ laser pulses at 30 ps pulse duration, being limited to an intensity of $ {10^{18}}\;{\rm W}/{{\rm cm}^2} $1018W/cm2 by the large focal spot size of $ \approx 100\;{\unicode{x00B5}{\rm m}} $≈100µm. Due to the setup complexity of NIF, changing the location of the final focusing parabola in order to improve the focal spot size is not an option. This leads to the possible use of disposable ellipsoidal plasma mirrors (PMs) placed within the chamber, close to the target in an attempt to refocus the four ARC beams. However, the behavior of PMs at these relatively long pulse durations (tens of picoseconds) is not well characterized. The results from the COMET laser at the Jupiter Laser Facility carried out at 0.5 to 20 ps pulse durations on flat mirrors are presented as a necessary first step towards focusing curved mirrors. The findings show defocusing at longer pulse durations and higher intensities, with less degradation when using aluminum coated mirrors.

Bremsstrahlung spectrum and photon dose from short-pulse high-intensity laser interaction on various metal targets

During the interaction of an intense picosecond laser pulse with a plasma created by a plastic foil ablated by a nanosecond laser pulse, relativistic electrons are produced. A metal solid target placed behind the foil allows converting these high-energy electrons into hard X-rays. The use of an ablated CH foil allows maximizing the conversion efficiency and thus the X-ray emission. In this study, the photon energy spectrum and dose are measured for different thicknesses of various metal targets such as tantalum. Numerical simulations including hydrodynamical radiative, particle-in-cell, and Monte Carlo codes are made to give comparison with the experimental data. These are also compared with that of a bremsstrahlung emission and photon dose model in which the energy loss by Ohmic heating arising from the return current driven by the background electrons of the conductive target is taken into account [A. Compant La Fontaine, Phys. Plasmas 25, 043301 (2018)]. The results obtained allow for benchmarks to test the accuracy of this model and to check that the dose is maximized for high-Z solid targets and thickness in the mm range in the relativistic interaction regime at ultrahigh laser intensity (>1018 W/cm2).

Requirements and sensitivity analysis for temporally- and spatially-resolved thermometry using neutron resonance spectroscopy.

Neutron resonance spectroscopy (NRS) has been used extensively to make temperature measurements that are accurate, absolute, and nonperturbative within the interior of material samples under extreme conditions applied quasistatically. Yet NRS has seldom been used in dynamic experiments. There is a compelling incentive to do so because of the significant shortcomings of alternative techniques. An important barrier to adopting dynamic NRS thermometry is the difficulty in fielding it with conventional spallation neutron sources. To enable time-dependent and spatially resolved temperature measurements in dynamic environments, more compact neutron sources that can be used at user facilities in conjunction with other diagnostic probes (such as x-ray light sources) are required. Such sources may be available using ultrafast high-intensity optical lasers. We evaluate such possibilities by determining the sensitivities of the temperature estimate on neutron-beam and diagnostic parameters. Based on that evaluation, requirements are set on a pulsed neutron-source and diagnostics to make a meaningful dynamic temperature measurement. Dynamic thermometry measurements are examined in this context when driven by two alternative fast-neutron sources: the Los Alamos Neutron Scattering Center (LANSCE) proton accelerator driving isotropic spallation neutrons as a baseline and a laser-plasma ion accelerator driving a neutron beam from deuterium breakup. Strategies to close the gap between the required and demonstrated performance of laser-based fast-neutron sources are presented. A short-pulse high-intensity laser with state-of-the-art pulse contrast and an energy of a few hundred Joules would drive a compact neutron source suitable for NRS thermometry that could transform the dynamic study of materials.

Space and time resolved measurement of surface magnetic field in high intensity short pulse laser matter interactions

Magnetic fields produced by the interaction of intense laser beams on the surface of flat solid targets have been characterized. Laser probe polarimetry diagnosed the spatial and temporal evolution of the magnetic field by measuring the changes in the probe beam polarization due to Cotton-Mouton and Faraday effects at different times with respect to a pump laser pulse. The results show that 1 ps after the interaction of the pump laser with the target, a magnetic field of the order of a few MG is already present over a region ≈150 μm in diameter centered around the interaction spot. From the spatial and temporal evolutions of the magnetic field, we infer information on the resistivity of the material, showing evidence of a strongly magnetized resistivity.

Optimization of laser-nanowire target interaction to increase the proton acceleration efficiency

We report on improved proton acceleration from the interaction of a short pulse high intensity laser (>1020 Wcm−2) with nano-engineered targets. Planar targets (from 7 to 20 μm) with protruding gold nanowires having different total areal densities, lengths, and diameters, ranging from 3% to 60% of the size of the laser focal spot were used during an experimental campaign at the 3 J, 30 fs HERCULES laser facility. The results show the importance of the average number of nanowires per focal spot, N, on laser energy absorption. We show that the proton acceleration is significantly improved by using 1 nanowires per focal spot. Detailed analysis indicates that 1 nanowire per focal spot optimizes the interaction between laser pulse and nanowires, in which the wings of the pulse pull out electrons from the wires forming a plasma with density that allows for deep penetration of the laser pulse into the array. When moving away from this optimum in both directions, N ≪ 1 and N ≫ 1, the laser pulse-nanowire coupling is either too weak or unfavorable for obtaining maximum proton energy. Proton spectra are compared to simulations using 2D-3V particle-in-cell code which reproduces the experimental data with good agreement.

Spectral Manipulation of Raman Amplifiers

Backward Raman amplifiers provide a promising path to the next generation of short pulse high-intensity lasers that can go beyond the damage limit of conventional materials. The main idea is to couple a short seed and a long counter-propagating pump through an electron plasma wave in such a way that the pump energy is transferred to the seed that is amplified and compressed via Raman backscattering. This paper will shortly review the physics of Raman amplifiers including two recent developments in the field: (a) mitigating the relativistic phase-mismatch and the resulting saturation by detuning of the pump pulse and (b) multi-frequency amplification of pulses with a beat-wave waveform.

Effect of laser noise on the propagation of laser radiation in dispersive and nonlinear media

The effect of laser noise on the atmospheric propagation of high-power CW lasers and high-intensity short pulse lasers in dispersive and nonlinear media is studied. We consider the coupling of laser intensity noise and phase noise to the spatial and temporal evolution of laser radiation. High-power CW laser systems have relatively large fractional levels of intensity noise and frequency noise. We show that laser noise can have important effects on the propagation of high-power as well as high-intensity lasers in a dispersive and nonlinear medium such as air. A paraxial wave equation, containing dispersion and nonlinear effects, is expanded in terms of fluctuations in the intensity and phase. Longitudinal and transverse intensity noise and frequency noise are considered. The laser propagation model includes group velocity dispersion, Kerr, delayed Raman response, and optical self-steepening effects. A set of coupled linearized equations are derived for the evolution of the laser intensity and frequency fluctuations. In certain limits, these equations can be solved analytically. For example, we find that, in a dispersive medium, frequency noise can couple to and induce intensity noise (fluctuations) and vice versa. At high intensities, the Kerr effect can reduce this intensity noise. In addition, significant spectral modification can occur if the initial intensity noise level is sufficiently high. Finally, our model is used to study the transverse and longitudinal modulational instabilities. We present atmospheric propagation examples of the spatial and temporal evolution of intensity and frequency fluctuations due to noise for laser wavelengths of 0.85 μm, 1 μm, and 10.6 μm.