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 K!$K!$ , with K$K$ 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.

In this paper, we propose a simple and experimentally feasible method to suppress non-dipole effects in strong-field ionization by introducing a weak bichromatic control field polarized along the laser-field propagation direction. Within the framework of the non-dipole strong-field approximation, we derive the form of this control field and demonstrate that it compensates the leading magnetic-field-induced drift in the photoelectron momentum distribution. Numerical simulations for helium atom show that the control field restores the dipole-like photoelectron spectrum and electron trajectories for both direct and rescattered electrons. While residual non-dipole contributions remain in the ionization matrix element and rescattering action, their influence on the observables is minor. The proposed approach provides a transparent means of isolating and controlling non-dipole effects and offers new opportunities for exploring their role in complex field configurations as well as in strong-field electron dynamics.

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.

The complete classification of the saddle-point solutions for high-order above-threshold ionization, presented in and for a linearly polarized laser field, is generalized to the case of an arbitrary bichromatic elliptically polarized field. We first present the classification of the saddle-point solutions for the case of a monochromatic elliptically polarized driving field, which is the simplest example of the field that has two components, i.e., that evolves in the plane. For a bichromatic laser field whose elliptically polarized components have the frequencies rω and sω (r and s are integers, s>r, and ω is the fundamental frequency), the system of the saddle-point equations has 8s2 solutions per optical cycle. One-half of these solutions are the so-called backward-scattering solutions for which the direction of the electron motion is significantly affected by the rescattering. The other half are the forward-scattering solutions for which the electron is only slightly deflected during the rescattering event. For some specific field configurations, the number of saddle-point solutions can be smaller. For example, for a bicircular field, which consists of two counterrotating circularly polarized components, there are 4s(r+s) solutions, while for the corotating configuration there are 4s2 solutions. As an application, we have shown that for a monochromatic elliptically polarized laser field, all four threshold anomalies appear in the spectra of the rescattered photoelectrons.

For decades the strong-field approximation (SFA) has been a theoretical backbone for describing the strong-field related phenomena such as above-threshold ionization (ATI) and high-order harmonic generation, even though it is well-known that it cannot accurately account for the long-range Coulomb interaction between the liberated electron and residual atomic ion. In this paper, we theoretically investigate high-order ATI. We use numerical solutions of the time-dependent Schrödinger equation (TDSE) and an improved SFA that includes electron rescattering. The analysis is performed for atomic anions and neutral atoms exposed to elliptically polarized laser fields. To validate the SFA and test its applicability, we compare both theoretical approaches for various targets and laser field parameters. We also show that the improved SFA in which the final electron plane wave is replaced by the Coulomb distorted plane wave leads to a better agreement with the results obtained using the solutions of the TDSE.

When the strong-field ionization of atoms is induced by an ultrashort pulse instead of a long pulse with a flat envelope, many symmetry properties of the photoelecton momentum distribution are broken. The induced asymmetry is measured using the asymmetry parameter which depends on the values of the driving-pulse parameters and the type of the target. We investigate the driving pulses with two carrier frequencies because in this case the dependence of the asymmetry on the characteristics of the target is more robust. Particular attention is devoted to the pulse which consists of two circularly polarized few-cycle waves and the pulse which has two linearly polarized components with mutually orthogonal polarizations. In the former case, we show that the asymmetry parameter is highly sensitive to the ionization potential and to the structure of the ground state. This is particularly the case for the photoelectron energy just above the value for which the contribution of the electrons which do not interact with the core after the ionization becomes negligible. We explain this sensitivity by investigating the dependence of the short-travel-time saddle-point solutions on the characteristics of the target. On the other hand, for the driving pulse with linearly polarized components, the dependence of the asymmetry parameter on the ionization potential is significant, while the dependence on the structure of the ground state is relatively small. In conclusion, we show that the characteristics of the target are imprinted in the asymmetry parameter and this signature is more pronounced for two-component pulses than for the linearly polarized driving pulse with one carrier frequency. Published by the American Physical Society 2025

The saddle-point solutions for strong-laser-field-induced high-order above-threshold ionization, the complete classification of which was recently presented in , are considered classically. In the limit of vanishing ionization potential the system of saddle-point equations simplifies, allowing a semi-analytical treatment. For a monochromatic field, the analytical nonlinear equations obtained this way allow one to determine the maximum (cutoff) photoelectron energies for the backward- and forward-scattering saddle-point solutions for all values of the multi-indices introduced by our classification scheme. These cutoffs are determined for all photoelectron momenta and it is shown how the backward-scattering solutions from one half of the momentum plane are related to the forward-scattering solutions from the other. The case of a bichromatic linearly polarized field is analyzed in detail. The results are rederived with the help of a simple graphical method, which can be used to qualitatively discuss the effect of varying the field parameters. Published by the American Physical Society 2025