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Two- and Three-Photon Partial Photoionization Cross Sections of Li+, Ne8+ and Ar16+ under XUV Radiation
摘要： In this work, we present the photon energy dependence of the two- and three-photon cross sections of the two-electron Li+, Ne8+ and Ar16+ ions, following photoionization from their ground state. The expressions for the cross sections are based on the lowest-order (non-vanishing) perturbation theory for the electric field, while the calculations are made with the use of an ab initio configuration interaction method. The ionization cross section is dominated by pronounced single photon resonances in addition to peaks associated with doubly excited resonances. In the case of two-photon ionization, and in the non-resonant part of the cross section, we find that the 1D ionization channel overwhelms the 1S one. We also observe that, as one moves from the lowest atomic number ion, namely Li+, to the highest atomic number ion, namely Ar16+, the cross sections generally decrease.
关键词： free-electron laser,X-ray radiation,cross sections,lowest-order perturbation theory,multiphoton ionization
更新于2025-09-23 15:23:52
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Analysis of the S1 ← S0 and D0 ← S1 spectra in m-bromofluorobenzene via resonance-enhanced multiphoton ionization and slow electron velocity-map imaging spectroscopy
摘要： Vibrations of m-bromofluorobenzene (m-BrFPh) in the first excited state (S1) and the cationic ground state (D0) are investigated by resonance-enhanced multiphoton ionization (REMPI) spectroscopy and slow electron velocity-map imaging (SEVI) spectroscopy, respectively. Quantum chemical calculations have been adopted to assign the observed vibrational bands, as well. The band origin of the S1 ← S0 electronic transition defines the adiabatic excitation energy to be 36987 ± 4 cm-1 based on the resonance-enhanced one-color two-photon ionization spectrum of m-BrFPh. And adiabatic ionization potential (IP) of 73903 ± 8 cm?1 is determined from band origin in the SEVI spectra. Meanwhile, the computed frequencies are in excellent agreement with the experimental observations and Franck-Condon simulations are performed to aid us to confidently assign major vibrational modes in S1 and D0 states. And the changes in the wavenumber of the vibrational modes upon S1 ← S0 and D0 ← S1 transitions are examined. Furthermore, the mixing of vibrational modes both between S0 & S1 and between S1 & D0 has been discussed.
关键词： Duschinsky mixing,Slow electron velocity-map imaging (SEVI),m-bromofluorobenzene,resonance-enhanced multiphoton ionization (REMPI)
更新于2025-09-23 15:21:01
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Time correlation inside a laser pulse
摘要： Looking inside a laser pulse by detecting an instantaneous ionization rate (IIR) has been a useful instrument for characterizing subcycle ionization dynamics [Phys. Rev. A 64, 013409 (2001)]. However, this instrument relies entirely on IIR being a deterministic function of time. By introducing an IIR operator and studying its autocorrelation function, we show that electron ionization dynamics is more complex and the ionization rate depends on the “prehistory,” i.e., the IIRs at the two instants of time are, in fact, correlated. The pattern of this correlation changes dramatically between the multiphoton and tunneling ionization regimes. These findings have wide implications for strong-field atomic physics and providing new possibilities for quantum local realism tests.
关键词： multiphoton ionization,laser pulse,tunneling ionization,instantaneous ionization rate,quantum local realism,subcycle ionization dynamics
更新于2025-09-23 15:19:57
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Laser Mass Spectrometry
摘要： Mass spectrometry (MS) has been used in a broad range of applications, in chemical, biochemical, pharmaceutical, and environmental fields. Lasers have many uses in MS, such as laser desorption (LD), laser desorption ionization (LDI), matrix-assisted laser desorption ionization (MALDI), and multiphoton ionization (MPI). Herein, recent developments and applications of mass spectrometry with laser beams, including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), are introduced.
关键词： laser desorption,matrix-assisted laser desorption ionization,multiphoton ionization,Laser abrasion,laser desorption/ionization
更新于2025-09-23 15:19:57
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The impact of nano-bubbles on the laser performance of hafnia films deposited by oxygen assisted ion beam sputtering method
摘要： Hafnia is a high refractive index material used in the manufacturing of dielectric coatings for next generation lasers. The formation of defects during deposition is the major barrier to realizing high laser-damage resistant coatings for future high energy density laser applications. Understanding the precursors responsible for laser-induced damage in hafnia is therefore critical. In this work, we investigate the mechanism of laser-induced damage in 90-nm thick hafnia films produced by an oxygen assisted dual ion beam sputtering (IBS) process. Under pulsed, nanosecond ultraviolet laser exposure (355 nm, 8 ns), the laser-induced damage onset is found to be strongly dependent on the amount of argon and excessive oxygen entrapped in the nanobubbles within the hafnia films. The presence of nanobubbles is revealed and confirmed by small angle X-ray scattering and scanning/transmission electron microscopy coupled with high-angle annular dark-field. The damage onset is stable initially but decreases as the energy of oxygen goes beyond 100 eV. The damage initiation is ascribed to a laser-induced plasma generation within the nanobubbles through multiphoton ionization. The results reveal that nanobubbles formed in the IBS produced coatings are a potent precursor. Although nanobubbles are commonly present in IBS films, their negative impact on laser damage resistance of hafnia films has not been previously recognized. Our findings provide a fundamental basis for the development of potential mitigation strategies required for the realization of laser damage resistant hafnia films.
关键词： laser-induced damage,multiphoton ionization,ion beam sputtering,hafnia,nanobubbles
更新于2025-09-16 10:30:52
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Modeling tomographic measurements of photoelectron vortices in counter-rotating circularly polarized laser pulses
摘要： Recent experiments [D. Pengel, S. Kerbstadt, L. Englert, T. Bayer, and M. Wollenhaupt, Phys. Rev. A 96, 043426 (2017)] have measured the photoelectron momentum distribution for three-photon ionization of potassium by counter-rotating circularly polarized 790-nm laser pulses. The distribution displays spiral vortices, arising from the interference of ionizing wave packets with different magnetic quantum numbers. The high level of multidimensional detail observed in the distribution makes this an ideal case in which to demonstrate the accuracy of emerging theoretical techniques applicable to such problems. We use the R-matrix with time dependence approach to investigate this process. We calculate the full-dimensional photoelectron momentum distribution, and compare against a set of planar projections of this distribution previously measured in experiment.
关键词： multiphoton ionization,potassium,photoelectron vortices,counter-rotating circularly polarized laser pulses,R-matrix with time dependence
更新于2025-09-12 10:27:22
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Scaling relations of the time-dependent Dirac equation describing multiphoton ionization of hydrogenlike ions
摘要： Approximate scaling laws with respect to the nuclear charge are introduced for the time-dependent Dirac equation describing hydrogenlike ions subject to laser fields within the dipole approximation. In particular, scaling relations with respect to the laser wavelengths and peak intensities are discussed. The validity of the scaling relations is investigated for two-, three-, four-, and five-photon ionization of hydrogenlike ions with nuclear charges ranging from Z = 1 to 92 by solving the corresponding time-dependent Dirac equations adopting the properly scaled laser parameters. Good agreement is found and thus the approximate scaling relations are shown to capture the dominant effect of the response of highly charged ions to intense laser fields compared to that of atomic hydrogen. On the other hand, the remaining differences are shown to allow for the identification and quantification of additional, purely relativistic effects in light-matter interaction.
关键词： scaling laws,time-dependent Dirac equation,relativistic effects,hydrogenlike ions,multiphoton ionization
更新于2025-09-09 09:28:46
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Universality of photoelectron circular dichroism in the photoionization of chiral molecules
摘要： Photoionization of chiral molecules by circularly polarized radiation gives rise to a strong forward/backward asymmetry in the photoelectron angular distribution, referred to as photoelectron circular dichroism (PECD). Here we show that PECD is a universal effect that reveals the inherent chirality of the target in all ionization regimes: single photon, multiphoton, above-threshold and tunnel ionization. These different regimes provide complementary spectroscopic information at electronic and vibrational levels. The universality of the PECD can be understood in terms of a classical picture of the ionizing process, in which electron scattering on the chiral potential under the influence of a circularly polarized electric field results in a strong forward/backward asymmetry.
关键词： strong fields,photoelectron circular dichroism,chirality,multiphoton ionization
更新于2025-09-09 09:28:46
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Role of Multiphoton Ionization in the Short-Wavelength Broadening of the Spectrum of a Light Bullet in the Middle Infrared Range
摘要： The short-wavelength cutoff of the anti-Stokes wing of the supercontinuum in the spectrum of a light bullet at filamentation of femtosecond radiation at a wavelength tunable in a wide range of the middle infrared range in fused silica and fluorides has been studied for the first time. A physical model for the formation of the spectrum of the light bullet has been proposed on the basis of the spectral broadening caused by the phase self-modulation of the light field on the trailing edge of the light bullet at the generation of a plasma in the process of multiphoton ionization. Within this model, a function has been obtained to determine the wavelength shift of the short-wavelength cutoff as a function of the multiphoton order. This function is in agreement with experimental results.
关键词： supercontinuum,light bullet,spectral broadening,multiphoton ionization,middle infrared range
更新于2025-09-04 15:30:14