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Diagnostics of ultra-intense laser pulses using tunneling ionization
摘要： We revisit a recently proposed scheme (Ciappina et al 2019 Phys. Rev. A 99 043405) for accurate measurement of electromagnetic radiation intensities in a focus of high-power laser beams. The method is based on the observation of multiple sequential tunneling ionization of atoms and suggests determination of the peak intensity value from the appearance in the focal area ions with a certain charge number. Here we study the sensitivity of the approach to two essential factors: the focal volume effect and the tunneling ionization model chosen to calculate ionization rates. We show, on the one hand, that the results appear almost model independent for ionization of helium- and hydrogen-like ions and, on the other hand, that the focal averaging leaves the intensity-dependent features visible. Our findings are in favor to a practical implementation of the atomic diagnostics of extreme laser intensities.
关键词： intensity diagnostic,tunneling,extreme light fields,petawatt lasers,strong-field ionization
更新于2025-09-19 17:13:59
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Influence of polarization on back-reflected e<sup>-</sup> e<sup>+</sup> pair jets from laser-electron collision
摘要： We investigate the effect of laser polarization on spatial and momentum distribution of back-reflected e? e+ pairs from the collision of an intense laser pulse (I = 5 × 1022 W/cm2) with a counter-propagating 5 GeV electron beam. During the pair production, a significant amount of particles (106 ? 107) are ejected in the opposite direction of the incoming electron beam (back-reflected), they are trapped by and co-propagate with the laser beam, gaining energy up to the GeV level. From our multi-dimensional particle-in-cell studies, we observe that laser polarization affects the angular distribution of these particles: a linearly polarized pulse produces two transversely separated particle jets, while a circular one leads to the formation of a radially symmetric cone-shaped emission. The results presented here add insights for future experiments performed at multi-PW laser facilities.
关键词： particle-in-cell,radiation reaction,strong-field QED,pair production,electron positron jets
更新于2025-09-12 10:27:22
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Topological strong-field physics on sub-laser-cycle timescale
摘要： The sub-laser-cycle timescale of the electronic response to strong fields enables attosecond dynamical imaging in atoms, molecules and solids, with optical tunnelling and high-harmonic generation the hallmarks of attosecond optical spectroscopy. Topological insulators are intimately linked with electron dynamics, as manifested via the chiral edge currents, but it is unclear if and how topology leaves its mark on optical tunnelling and sub-cycle electronic response. Here, we identify distinct bulk topological effects on directionality and timing of currents arising during electron injection into conduction bands. We show that electrons tunnel differently in trivial and topological insulators, for the same band structure, and identify the key role of the Berry curvature in this process. These effects map onto topologically dependent attosecond delays and helicities of emitted harmonics that record the phase diagram of the system. Our findings create new roadmaps in studies of topological systems, building on the ubiquitous properties of the sub-laser-cycle strong-field response—a unique mark of attosecond science.
关键词： high-harmonic generation,attosecond science,Berry curvature,topological insulators,strong-field physics
更新于2025-09-12 10:27:22
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Laser‐Driven Strong‐Field Terahertz Sources
摘要： A review on the recent development of intense laser-driven terahertz (THz) sources is provided here. The technologies discussed include various types of sources based on optical rectification (OR), spintronic emitters, and laser-filament-induced plasma. The emphasis is on OR using pump pulses with tilted intensity front. Illustrative examples of newly emerging applications are briefly discussed, in particular strong-field THz control of materials and acceleration and manipulation of charged particles.
关键词： plasma-based terahertz sources,optical rectification,spintronic emitters,terahertz pulses,strong-field terahertz–matter interactions
更新于2025-09-11 14:15:04
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RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schr?dinger equation for general, multielectron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses
摘要： RMT is a program which solves the time-dependent Schr?dinger equation for general, multielectron atoms, ions and molecules interacting with laser light. As such it can be used to model ionization (single-photon, multiphoton and strong-field), recollision (high-harmonic generation, strong-field rescattering) and, more generally, absorption or scattering processes with a full account of the multielectron correlation effects in a time-dependent manner. Calculations can be performed for targets interacting with ultrashort, intense laser pulses of long wavelength and arbitrary polarization. Calculations for atoms can optionally include the Breit-Pauli correction terms for the description of relativistic (in particular, spin-orbit) effects.
关键词： electron correlation,R-matrix,ionization,strong-field physics,ultrafast physics,Attosecond physics
更新于2025-09-11 14:15:04
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Semiclassical analysis of photoelectron interference in a synthesized two-color laser pulse
摘要： We measure the photoelectron energy spectra from strong-field ionization of Kr in a two-color laser pulse consisting of a strong 400-nm field and a weak 800-nm field. The intensities of the main above-threshold ionization (ATI) and sideband peaks in the photoelectron energy spectra oscillate roughly oppositely with respect to the relative phase between the two-color components. We study the photoelectron interferometry in the strong-field ATI regime from the view of interference of different electron trajectories in order to extend reconstruction of attosecond harmonic beating by interference of two-photon transitions (RABBITT)-type analysis to the strong-field regime. Based on the strong-field approximation model, we obtain analytical expressions for the oscillations of both ATI and sideband peaks with the relative phase. A phase shift of π/4 with respect to the field maximum of the two-color laser pulse is revealed for the interference maximum in the main ATI peak without including the effect of the atomic potential.
关键词： ATI,RABBITT,photoelectron interference,two-color laser pulse,strong-field ionization,sideband peaks
更新于2025-09-11 14:15:04
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Strong-field- versus weak-field-ionization pump-probe spectroscopy
摘要： Ionization can serve as a universal probe of excited-state dynamics in molecules, such as internal conversion, dissociation, and isomerization. These processes are of fundamental importance to a wide array of dynamics in biology, chemistry, and physics. In recent years, there has been significant debate about the relative merits of strong-field ionization (SFI), which involves multiphoton absorption, versus weak-field ionization (WFI), where a single photon is absorbed, as probes of these dynamics. SFI is advantageous because it uses wavelengths that are relatively easy to generate, and one can always ionize the molecule with sufficient intensity. However, for SFI it is difficult to calculate observables, such as the time-dependent ion yield, since the calculation of the ionization dynamics including multiphoton processes is computationally expensive and difficult to carry out for many molecular geometries. WFI has the advantage that calculations of observables are tractable. However, the generation and implementation of the appropriate wavelengths (photon energies) can be challenging, and the fixed energy of the probe can lead to technical complications in following the dynamics from excited states back down to the ground state. Here we present a quantitative comparison of the two approaches for following the excited-state dynamics of two molecules, diiodomethane and uracil. The combination of internal conversion and dissociation in these molecules provides an ideal comparison of WFI and SFI as a probe. We compare the measurements with calculations of the dynamics. Our work indicates that while SFI and WFI provide qualitatively similar information about the excited-state dynamics, only WFI results can be compared quantitatively with present-day calculations.
关键词： strong-field ionization,diiodomethane,uracil,weak-field ionization,excited-state dynamics
更新于2025-09-10 09:29:36
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Coulomb potential effects in strong-field atomic ionization under elliptical polarization
摘要： We experimentally and theoretically investigate strong-field ionization of noble-gas atoms in elliptically polarized laser fields at 2000 nm. The ellipticity dependence of the ion yields has been measured at a series of intensities and compared to various theoretical model predictions [i.e., the Ammosov-Delone-Krainov (ADK), strong-field approximation (SFA), and Coulomb-Volkov distorted-wave approximation (CVA) models]. The SFA and ADK calculations match each other, which alludes to the negligible contribution of nonadiabatic effect. In the meantime, they both deviate significantly from the measurements. On the other hand, the good agreement between CVA calculations and measurements reveals the salient role played by the Coulomb potential in atomic ionization. The Coulomb potential effect is further confirmed by comparison of CVA calculations and measurements at 800 nm. Our work demonstrates the significant Coulomb potential effect on the ionization yields, the experimental evidence of which has rarely been documented.
关键词： strong-field ionization,elliptically polarized laser fields,CVA theory,ADK model,SFA theory,Coulomb potential
更新于2025-09-10 09:29:36
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High-energy direct photoelectron spectroscopy in strong-field ionization
摘要： Recently, in the tunneling regime of strong-field ionization an unexpected Coulomb field effect has been identified by numerical solution of the time-dependent Schr?dinger equation [Phys. Rev. Lett. 117, 243003 (2016)] in photoelectron spectra in the upper energy range of the direct electrons. We investigate the mechanism of the Coulomb effect employing a classical theory with Monte Carlo simulations of trajectories, and a quantum theory based on the generalized eikonal approximation for the continuum electron. The effect is shown to have a classical nature and is due to momentum space bunching of photoelectrons released not far from the peak of the laser field. Moreover, our analysis reveals specific features of the angular distribution of high-energy direct electrons, which can be employed for molecular imaging. For the H2+ molecule as an example we show the signatures of the molecule orientation and the molecular structure in the investigated angular distribution.
关键词： Coulomb field effect,generalized eikonal approximation,photoelectron spectra,strong-field ionization,molecular imaging
更新于2025-09-09 09:28:46