Superintense Laser Research Articles

Spatiotemporal aberrations due to the groove density mismatching of compression gratings in ultra-intense femtosecond lasers

The groove density mismatching of compression gratings, an often-neglected key issue, can induce significant spatiotemporal aberrations especially for super-intense femtosecond lasers. We mainly investigate the angular chirp and the consequent degradation of the effective focused intensity introduced by the groove density mismatching of compression gratings in ultra-intense femtosecond lasers. The results indicate that the tolerances of grating groove density mismatching will rapidly decrease with the beam aperture or spectral bandwidth increases. For our 100PW laser under construction, the grating groove density mismatching should be as small as 0.001 gr/mm if the drop of effective focused intensity has to be controlled below 15%. More importantly, new angular chirp compensation schemes are proposed for both double-grating and four-grating compressors. This work reveals the importance of groove density matching of compression gratings, and can provide helpful guidelines for the design of ultra-intense femtosecond lasers.

Laser-driven production with advanced targets of Copper-64 for medical applications

Radionuclides are of paramount importance in nuclear medicine both for clinical uses and radiopharmaceutical production. Among the others, nuclides suitable for theranostics like Copper-64 are particularly attractive since they can play both a diagnostic and therapeutic role. In the last years, the growing demand for these nuclides stimulated the research of new solutions, along with cyclotrons already in use, for their production. In this respect, a promising alternative is laser-driven proton accelerators based on the interaction of superintense laser pulses with target materials. Because of their potential compactness and flexibility, they are under investigation for several applications ranging from materials science to nuclear medicine. Moreover, the use of advanced Double-Layer targets (DLTs) was identified as a viable route to increase the number and energy of the accelerated protons to satisfy the requirements of demanding applications. In this contribution, we numerically investigate the use of DLT-based laser-driven sources for Copper-64 production. We show that activities relevant to pre-clinical studies can be achieved with an existing 150 TW laser and DLTs. Moreover, we extend the discussion by considering a broad range of laser systems by exploiting a theoretical model. Our results can guide the choice of laser and target parameters for future experimental investigations.

Numerical Simulations of the Acceleration of Fast Protons and of the Excitation of Nuclear Reactions 11B(p, 3a) and 11B(p, n)C11 at the Intensities of Picosecond Laser Radiation in the Range 1018-1019 W/cm2

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 I = 1018 W/cm2 to I = 1019 W/cm2 at the fixed laser pulse duration. The obtained parameters of proton beams were used for calculation of the total yield of a particles and neutrons for the nuclear reactions 11B(p, 3a) and 11B(p, n)C11C at the collisions of proton beams with boron targets. It is shown that the number of a particles escaping boron target and arriving at track detectors is less than 5of the total amount of a particles, because the majority of these particles remain inside the target owing to ionization losses. The derived values of the yield ofparticles’ which arrive at detectors are in good agreement with the experimental data. We also calculate the total yield of neutrons in the reaction 11B(p, n)C11C. It is found that, at the intensity I = 1019 W/cm2 of the picosecond laser pulse, the yield is equal to Nn = 1.4 × 108 , this value is approximately of 3% of the total yield of a particles.

Direct calibration of neutron detectors for laser-driven nuclear reaction experiments with a gated neutron source.

Nowadays, the sustained technological progress in high-intensity lasers is opening up the possibility of super-intense laser pulses to trigger or substantially influence nuclear reactions. However, it is a big challenge to quantitatively measure the reaction products because of the interference of electromagnetic pulses induced by high-intensity lasers. Fast scintillation detectors are widely chosen for fast neutron detection. The calibration of neutron detectors is crucial to measuring the yield of neutron products. Since one large signal superimposed by a number of neutron signals appears during a short period, it is difficult to directly and precisely calibrate the detectors' response for a single neutron. In the present work, we developed a direct calibration method with a gated fission neutron source 252Cf to solve this problem. This work demonstrates that the gated fission neutron source approach, with a unique "Pulse Shape Discrimination & Time of Flight window" function, has the highest background-γ-rejection and improves the confidence level of the final results for both liquid and plastic scintillator. Compared with the result of Compton edge method and neutron beam method, the gated fission neutron source method achieves much cleaner neutron signals and avoids interference caused by the modeling accuracy of the neutron detectors. This approach can be widely used in laser-driven nuclear physics experiments with higher accuracy for neutron detection.

Laser-induced topology optimized amorphous nanostructure and corrosion electrochemistry of supersonically deposited Ni30Cr25Al15Co15Mo5Ti5Y5 HEA coating based on AIMD

A novel Ni30Cr25Al15Co15Mo5Ti5Y5 high-entropy alloy (HEA) coating was irradiated to optimize its internal structure via laser after supersonic particle deposition (SPD). Owing to the high energy density of the laser and large temperature gradient, the crystallization process of the molecules and atoms in the coating was restrained and supercooling occurred. Experimental results showed that a considerable number of nano-crystal grains precipitated and amorphous structures were formed because of the random orientation of the crystals. The baseline of differential scanning calorimetry scans obtained for the coating started to shift at the Tg of 939.37 ℃ and a step was observed. Multiple dispersion peaks and lattice fringes indicated that the nucleation of the irradiated laser-induced topology optimized (LTO) coating was incomplete. The laser-induced topology optimizing treatment led to quasi-isotropy in the SPD coating. Furthermore, the LTO coating exhibited a residual stress of 18.4 MPa, stress-strain response, and fatigue limit of 265 MPa. Hence, the LTO coating exhibited higher performance than the unirradiated SPD coating. The Nyquist and Bode electrochemical impedance spectra of the LTO coating, including two relaxation processes, indicated that the corrosion process steadily recovered to the equilibrium state. This implies that the uniform oxidation passivation layer on the surface of the LTO coating insulated the material from the corrosive medium, protecting the substrate from further corrosion, thus enhancing the structural security of the material for use in super-intense laser facility applications.

Towards a direct measurement of the quantum-vacuum Lagrangian coupling coefficients using two counterpropagating super-intense laser pulses

In this paper we will show that photon–photon collision experiments using extreme lasers can provide measurable effects giving fundamental information about the essence of QED, its Lagrangian. A possible scenario with two counterpropagating ultra-intense lasers for an experiment to detect scattering between optical photons is analyzed. We discuss the importance of the pulse widths and waists, the best scenario for overlapping the beams and signal detection, as well as ways to distinguish the signal from the noise. This would need a high-precision measurement, with control of temporal jitter and noise. We conclude that such experiment is barely feasible at 1023 W cm−2 and very promising at 1024 W cm−2.

Measuring gravitational effect of superintense laser by spin-squeezed Bose–Einstein condensates interferometer

We consider an extremely intense laser, enclosed by an atom interferometer. The gravitational potential generated from the high-intensity laser is solved from the Einstein field equation under the Newtonian limit. We compute the strength of the gravitational force and study the feasibility of measuring the force by the atom interferometer. The intense laser field from the laser pulse can induce a phase change in the interferometer with Bose–Einstein condensates. We push up the sensitivity limit of the interferometer with Bose–Einstein condensates by spin-squeezing effect and determine the sensitivity gap for measuring the gravitational effect from intense laser by atom interferometer.

Chirp-dependent ionization of hydrogen atoms in the presence of super-intense laser pulses* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11774131 and 91850114).

We perform a theoretical study on dynamic interference in single photon ionization of ground state hydrogen atoms in the presence of a super-intense ultra-fast chirped laser pulse of different chirp types (equal-power and equal-FWHM laser pulses) by numerically solving the time-dependent Schrödinger equation in one dimension. We investigate the influences of peak intensity and chirp parameters on the instantaneous ionization rate and photoelectron yield, respectively. We also compare the photoelectron energy spectra for the ionization by the laser pulses with different chirp types. We find that the difference between the instantaneous ionization rates for the ionization of hydrogen atom driven by two different chirped laser pulses is originated from the difference in variation of vector potentials with time.

Relativistic stability of positronium atoms in a linearly polarized high frequency super-intense laser field

Utilizing the relativistically corrected Krammers-Henneberger (KH) potential in the high frequency Floquet theory (HFFT), the ground state of the positronium (Ps) atom in a linearly polarized high frequency super-intense laser field is investigated numerically. It is reported that the relativistic effect can prevent Ps from annihilating into γ rays, thus enhancing its stability. The underlying mechanism lies in the reconstruction of the electron wavefunction into a figure-of-eight shape, which leads to an effective reduction of the electron-positron overlapping probability.

Light sail boosted by instantaneous radiation pressure

Light sail acceleration by ultrashort, superintense laser pulses is presently investigated as an approach to compact accelerators of matter. The usual light sail equation assumes a cycle-averaged light pressure, which becomes questionable for ultrashort pulse drivers or in the highly relativistic regime. Here, we remove such assumption and compute solutions of the light sail equations which show oscillations of the sail acceleration. The dependence of the final sail velocity on the temporal profile of extremely short pulses is discussed.

Ultrafast Science to Capture Ultrafast Motions

We are living in a dynamic world, where all matter is in a vibrant process, whether it is a giant celestial body or a small atom. Being able to observe, analyze, and manipulate these dynamic processes is undoubtedly essential for scientific discoveries and technical innovations. The evolution of any physical quantity (e.g., displacement, mass, electromagnetic fields, intensity, phase, and spectra) with time gives rise to different time-varying phenomena—some are slow, some are fast, and some are ultrafast, in view of what human beings can sense. With the modern smartphone or camera, fast motions within the microsecond time scale can now be recorded in daily life. However, when we enter into the micro/nanoscale world, what happens often becomes ultrafast. For example, atomic diffusion occurs in a nanosecond (10–9s) time scale. Molecular rotation, charge transfer relaxation, and magnetization reversal happen in picoseconds (10–12s). Molecule and lattice vibrations can happen even faster, occurring in femtoseconds (10–15s). Looking into the depths of an atomic system, electrons move orders faster to the attosecond (10–18s), which is currently the fastest process that human beings can observe. Furthermore, when we explore the nucleus of an atom, we will find the ultrafast dynamics happening in zeptoseconds (10–21s). These ultrafast processes, which eventually govern the property of matter, need special pulsed probing sources, methods, and instruments to investigate. The related ultrafast technologies play important roles for research and applications in fundamental physics, chemistry, materials, biology, energy, and information science. Ultrafast science is a general term referring to a knowledge system to investigate and explore the phenomena and laws of ultrafast changes in the universe. It involves various disciplines including atom and molecule physics, condensed matter physics, mechanics, optics, chemistry, biology, material science, and information science. Thus, ultrafast science has developed rapidly in the past decades. The Nobel Prize in chemistry was awarded for femtosecond laser chemistry in 1999. The Nobel Prize in physics was awarded for optical frequency comb laser precision spectroscopy in 2005. The 2018 Nobel Prize in physics was awarded for ultrashort super-intense laser pulse technology—chirped pulse amplification. In the last 10 years, over 50,000 research articles have been published in over 1,000 journals, as analyzed by Web of Science using the keyword of “ultrafast.” However, there lacks a specific high-impact journal that focuses on ultrafast science. This is the motivation for launching the Ultrafast Science journal. After over 1 year of preparation and discussion with the American Association for the Advancement of Science (AAAS), we reached a consensus that ultrafast science is an emerging and important direction which covers very broad and leading research fields. In 2020, Ultrafast Science became a Science Partner Journal distributed by the AAAS in collaboration with Xi’an Institute of Optics and Precision Mechanics (XIOPM), which is one of the leading organizations in ultrafast science in China, from the Chinese Academy of Sciences (CAS). Ultrafast Science is an Open Access Journal which publishes top-quality original research articles, comprehensive reviews, and perspectives, reflecting significant advances, breakthroughs, and novel applications with considerable potential in ultrafast science and broad interest from scientific communities. Topics include but are not limited to ultrafast physics, ultrafast laser and application, ultrafast imaging, ultrafast spectroscopy, ultrafast measurement, ultrafast materials and devices, ultrafast terahertz photonics, ultrafast electronics, ultrafast chemical physics, and other ultrafast phenomena. Interdisciplinary research demonstrating how ultrafast technology advances physics, chemistry, biology, material science, and other disciplines is especially welcome. We are honored to serve as the founding Editors-in-Chief and are grateful to work with the members of the Editorial Board, which currently comprise around 40 famous scientists from all over the world, including Gerard Mourou, who was awarded the Nobel Prize in physics in 2018. We believe that Ultrafast Science will become a high-impact journal in the near future with all of your participation and contributions, and that the journal will grow with the continuous breakthroughs in the ultrafast frontier.

Evidence of radial Weibel instability in relativistic intensity laser-plasma interactions inside a sub-micron thick liquid target

Super-intense laser plasma interaction has shown great promise as a platform for next generation particle accelerators and sources for electron, x-rays, ions and neutrons. In particular, when a relativistic intense laser focus interacts with a thin solid density target, ionized electrons are accelerated to near the speed of light (c) within an optical cycle and are pushed in the forward and transverse directions away from focus, carrying a significant portion of the laser energy. These relativistic electrons are effectively collisionless, and their interactions with the ions and surrounding cold electrons are predominantly mediated by collective electromagnetic effects of the resulting currents and charge separation. Thus, a deeper understanding of subsequent high energy ions generated from various mechanisms and their optimization requires knowledge of the relativistic electron dynamics and the fields they produce. In addition to producing MV/m quasi-static fields, accelerating the ions and confining the majority of the electrons near the bulk of the laser target, these relativistic electron currents are subject to plasma instabilities like the Weibel instability as they propagate through the thermal population in the bulk target. In this work, we present high temporal (100 fs) and spatial (1 μm) resolution shadowgraphy video capturing relativistic radial ionization front expansion and the appearance of filamentation radiating from the laser spot within a sub-micron thick liquid sheet target. Filamentation within the region persists for several picoseconds and seeds the eventual recombination and heating dynamics on the nanosecond timescale. A large scale three-dimensional particle-in-cell (PIC) simulation of the interaction revealed the presence of strong magnetic fields characteristic of Weibel Instability, and corroborated the relativistic radial expansion of the ionization front, whose speed was determined to be 0.77c. Both the experimental and simulation results strongly point towards the target field ionization and the outward expanding hot electron current as the cause of the radial expansion.

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.

Symmetry breaking of Kramers-Henneberger atoms by ponderomotive force.

It was believed that Kramers-Henneberger (KH) atoms in a linearly polarized superintense laser field exhibit the structure of "dichotomy." At large quiver amplitude, the two lowest-lying eigenstates are degenerated and both have a dichotomous symmetric structure. However, this is not a common structure for KH atoms because KH atoms practically can only exist in the focused laser field. However, in a focused laser, KH state electrons usually experience the ponderomotive force, which will lift the degeneracy and break the symmetry.

Superintense Laser and its Related Devices

Superintense Laser and its Related Devices

Dynamic nuclear Stark shift in hydrogen-like U-238 via super-intense laser field

The dynamic nuclear Stark shift has been studied for Hydrogen-like U-238, under the indirect interaction of super-intense laser with nucleus via oscillating electron. The system of Hydrogen-like U-238 is chosen by keeping the available laser facilities in mind. The electron, oscillates under the influence of linearly polarized laser field, producing a variable electric field that interacts with the discrete nuclear levels. An appreciable Stark shift has been calculated in the nuclear levels for the variation in the intensity and frequency of the incident laser.

High-energy ionization for intense laser pulse diagnostics

To characterize super-intense laser fields is a very challenging task. We propose a method that enables a complete temporal characterization of the laser pulse, when driving ionization. The method relies on the fact that the photoelectron dynamics are basically governed by the laser field, despite the presence of a long-range Coulomb interaction. Thus, the properties of the incident field are imprinted on the photoelectron momentum distributions and, as envisaged by our calculations, can be determined using a velocity map imaging spectroscopy.

Energy calibration of a CR-39 nuclear-track detector irradiated by charged particles

Charged particle diagnosis is an important aspect of laser–plasma experiments conducted at super-intense laser facilities. In recent years, Columbia Resin #39 (CR-39) detectors have been widely employed for detecting charged particles in laser–plasma experiments. This is because the CR-39 polymer does not respond to electromagnetic pulses or X-rays. This study presents a method for calibrating the relationship between particle energy and track diameter in a CR-39 detector (TasTrak®) using 3–8 MeV protons, 6–30 MeV carbon ions, and 1–5 MeV alpha particles. The particle tracks were compared under the manufacturer’s recommended etching conditions of 6.25 mol/l NaOH at 98 °C and under the widely adopted experimental conditions of 6.25 mol/l NaOH at 70 °C. The results show that if the NaOH solution concentration is 6.25 mol/l, then the temperature of 70 °C is more suitable for etching proton tracks than 98 °C and employing a temperature of 98 °C to etch alpha-particle and carbon-ion tracks can significantly reduce the etching time. Moreover, this result implies that C3+ ion or alpha-particle tracks can be distinguished from proton tracks with energy above 3 MeV by controlling the etching time. This calibration method for the CR-39 detector can be applied to the diagnosis of reaction products in laser–plasma experiments.

Breakdown of the nonrelativistic approximation in superintense laser-matter interactions

We study the breakdown of the nonrelativistic approximation in the multiphoton ionization of atomic hydrogen by some intense x-ray laser pulse, in a regime where the dipole approximation is no longer valid. To this end, both the time-dependent Dirac equation as well as its nonrelativistic counterpart, the time-dependent Schr\odinger equation, are solved within an ab initio numerical framework. It is demonstrated that a recently developed semirelativistic Schr\odinger equation for superintense laser fields [Lindblom et al., Phys. Rev. Lett. 121, 253202 (2018)] yields results in excellent agreement with the fully relativistic treatment. The semirelativistic equation is then used in an investigation of the role of higher-order beyond-dipole corrections to the laser-matter interaction. The result of the present study can be summarized into two main findings: (1) relativistic effects predict a blueshift of the multiphoton ionization spectrum, and (2) higher-order beyond dipole corrections (beyond the leading-order term) indicate a corresponding redshift of the photoelectron spectrum. However, the two shifts turn out to be of the same order of magnitude, effectively leading to a net cancellation of their respective contributions. This apparent cancellation effect raises an important question: Is the distinction between relativistic blueshifts and higher-order beyond dipole redshifts meaningful from an experimental point of view? The result of the present study indicates that the answer is negative because the two effects nonetheless cannot be measured separately. Therefore, instead, we suggest that the present findings should merely be taken as a demonstration that caution should be exercised when higher-order beyond-dipole and relativistic corrections are to be taken into account in approximation schemes in the modeling of superintense laser-matter interactions.

Nuclear isomer excitation in Th229 atoms by superintense laser fields

Excitation of the isomeric nuclear state 229m Th in the process of thorium atom irradiation by two-color femtosecond pulse of Ti: Sa laser at the fundamental wavelength and second harmonic is analyzed. It is shown that the rate of isomeric state excitation can be enhanced significantly with respect to other nucleus excitation processes in laser plasma or by an external coherent source at the resonance wavelength. This enhancement is due to the process of nonlinear laser nuclear excitation based on the following. First, the atomic current associated with the motion of valence electrons in strong field is a nonlinear function of the field amplitude. Secondly, the energy of photons at frequency of the Ti:Sa laser fifth harmonic coincides with the energy of the 229m Th state. Yield of this harmonic is much higher if the two-color (1st and 2nd harmonics of the fundamental) is used. Thirdly, the intensity of the field produced by valence electrons at atomic nucleus reaches the near-atomic value, which exceeds significantly the field strength associated with any other mechanism of laser plasma emission.