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Physical Review A

High-order above-threshold ionization of an atom in intense quantum light

Shijun Wang, XuanYang Lai

Published Dec 1, 2023• 28 citations
Publisher

Abstract

We investigate high-order above-threshold ionization (HATI) from intense quantum light-atom interaction, by numerically solving the fully quantum time-dependent Schr\"odinger equation based on quantum electrodynamics theory. Our simulations show that, in comparison with coherent-state (classical) light, the HATI spectra from intense quantum lights may have a higher cutoff energy and, moreover, for a given ponderomotive energy of the laser field, the cutoff energy is dependent on the laser wavelength and the ionization potential of the atom. The influence of quantum light on the HATI is revealed by examining the interplay between a quasiprobability distribution of the electric field of the quantum light and the Ammosov-Delone-Krainov ionization rate of the atom. Furthermore, analytical formulas of the cutoff energy of the HATI spectra for different quantum lights are derived.

DOI
10.1103/physreva.108.063101

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Annalen der Physik•Mar 1, 2026•3 citations
We investigate high-order above-threshold ionization (HATI) from intense quantum light-atom interaction, by numerically solving the fully quantum time-dependent Schr"odinger equation based on quantum electrodynamics theory. Our simulations show that, in comparison with coherent-state (classical) light, the HATI spectra from intense quantum lights may have a higher cutoff energy and, moreover, for a given ponderomotive energy of the laser field, the cutoff energy is dependent on the laser wavelength and the ionization potential of the atom. The influence of quantum light on the HATI is revealed by examining the interplay between a quasiprobability distribution of the electric field of the quantum light and the Ammosov-Delone-Krainov ionization rate of the atom. Furthermore, analytical formulas of the cutoff energy of the HATI spectra for different quantum lights are derived.
Quantum theory of high-order above-threshold ionization (HATI) of atoms, prepared in a coherent superposition of bound states, by a strong laser field is formulated. Numerical results are obtained using the solutions of the time-dependent Schr\"odinger equation and the improved strong-field approximation. As an example, coherent superposition of the excited 2s2s2s and 2p2p2p states of the He atom is used. Applying a two-level model, it is shown how the relative amplitude and phase of the states in this coherent superposition can be controlled with a weak resonant laser pulse. Numerical results presented for HATI by a strong nonresonant probe laser pulse confirm that the photoelectron spectra and the momentum distributions strongly depend on the relative phase of the states in the prepared coherent superposition. For the case of HATI by a strong resonant laser pulse, we modify our strong-field-approximation theory by applying the two-level model to describe the time evolution of the atomic bound state before the instant of ionization. Contrary to the HATI from a single state by a long laser pulse, the corresponding photoelectron spectra of HATI from the coherent superposition of states depend on the carrier-envelope phase of the resonant ionizing pulse. Therefore, the strong-field ionization from a coherent superposition of states by a resonant laser pulse can be used to determine the carrier-envelope phase for long pulses for which the standard methods such as stereo--above-threshold ionization technique fail. The results strongly depend on the relative amplitude and phase of states in the coherent superposition of states, which can be controlled with a weak resonant laser pulse.
We study strong-field ionization by quantum lights with emphasis on high-order above-threshold ionization and the intensity-dependent enhancements in the photoelectron spectra. We find that the length of the plateau in the photoelectron energy spectrum generated by such quantum lights can be extended by an order of magnitude in comparison with that generated by the classical coherent laser light and that within this plateau resonantly enhanced groups of sharp peaks appear at energies which are integer multiple of the photon energy. We relate the observed intensity-dependent enhancements to the channel closing effect. Our results are particularly interesting in the context of the recent interplay and merging of quantum optics with strong-field physics and attoscience.
Squeezed coherent quantum light is described by the complex squeeze parameter ζ = s e i ϑ and the coherent-state displacement parameter β = | β | e i ϕ β . Our study of strong-field ionization [D. Habibović and D. B. Milošević, ], which focused on bright squeezed vacuum quantum light with β = 0 and s ≫ 1 , is extended to ionization by squeezed coherent light. It is shown that the amplitudes s and | β | strongly influence the ionization process, whereas phases ϑ and ϕ β play a less significant role. The present work provides a unified treatment of coherent, squeezed vacuum, and squeezed coherent light within a single theoretical framework. The quantum nature of the driving field is incorporated by averaging the strong-field ionization probability over the Husimi-Kano phase-space distribution. Using neon as a representative target, we analyze how the parameters characterizing squeezed coherent light modify photoelectron spectra and intensity-dependent enhancements. We show that nonclassical photon statistics can lead to a pronounced steepening of the rescattering plateau and, at low mean intensities, to an effective suppression of the nominal high-energy cutoff. These effects originate from the reduced weight of high-intensity field components inherent to squeezed states and have no analog in strong-field ionization driven by a coherent light. Our results highlight the potential for quantum-statistical control of strong-field ionization and provide a foundation for exploring laser-matter interactions driven by quantum light.
We present a theoretical study of the main characteristics of two-color photoionization spectra obtained when atoms are subjected to an intense radiation pulse containing the fundamental of an infrared laser and one of its higher harmonics. The frequency of the latter is chosen to be high enough that the atom can be ionized by a single photon. The calculation is performed by numerical integration of the time-dependent Schrödinger equation for a (three-dimensional) hydrogen atom. We present the general properties of the spectra and angular distributions as well as the possible occurrence of interferences between the laser-assisted process and above-threshold ionization. Our results indicate that such interference effects, which can lead to partial coherent control of the photoionization process, can be observed at moderate laser intensities within the reach of currently operated laser and harmonic sources.
Intense laser-matter interactions are at the center of interest in research and technology since the development of high-power lasers.They have been widely used for fundamental studies in atomic, molecular, and optical physics, and they are at the core of attosecond physics and ultrafast optoelectronics.Although the majority of these studies have been successfully described using classical electromagnetic fields, recent investigations based on fully quantized approaches have shown that intense laser-atom interactions can be used for the generation of controllable high-photon-number entangled coherent states and coherent state superpositions.In this tutorial, we provide a comprehensive fully quantized description of intense laseratom interactions.We elaborate on the processes of high-harmonic generation, above-threshold ionization, and we discuss new phenomena that cannot be revealed within the context of semiclassical theories.We provide the description for conditioning the light field on different electronic processes, and their consequences for quantum state engineering of light.Finally, we discuss the extension of the approach to more complex materials, and the impact to quantum technologies for a new photonic platform composed of the symbiosis of attosecond physics and quantum information science.
ABSTRACT Strong‐field ionization by thermal light is studied. Even though thermal light can be considered as completely classical stochastic light, it can also be treated as quantum light in the sense that it can be represented by a superposition of coherent states, similarly as has been done for the bright squeezed vacuum light, for example. Such a distribution over coherent states contains components with an intensity much higher than the average intensity of the thermal light. This increases the ionization probability by many orders of magnitude. For low intensities, in the multiphoton regime, the enhancement is by the factor of , with the multiphoton order of the process. This result is in agreement with an old experiment [ Phys. Rev. Lett . 32 (1974): 265] in which a similar enhancement factor appears if a multimode laser pulse is used instead of a single‐mode pulse. It is also shown that the plateau length in high‐order above‐threshold ionization by thermal light is extended by an order of magnitude in comparison with that of coherent laser light with the same average intensity.