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2Quasi-phase matching of elliptically polarized high-order harmonic generation by atomic systems in two-color laser fields
S. Stremoukhov1'2
1- Faculty of Physics, M.V Lomonosov Moscow State University, Leninskie Gory, 1/2, 119991 Moscow, Russia 2- National Research Centre "Kurchatov Institute", Akademika Kurchatova sq. 1, 123182 Moscow, Russia
High-order harmonic generation (HHG) in media exposed to intense laser field is one of the most actively studied non-linear optical phenomenon. To date, a significant number of methods have been developed to control the intensity, ellipticity and width of the spectrum of generated radiation. At the same time, the search for new ways to increase the efficiency of harmonic generation and control of their polarization properties continues [1]. The development of methods for generating intense harmonics with controlled polarization characteristics in a wide spectral range will make it possible not only to create a compact arbitrary polarized multispectral source of coherent radiation, but also to use the generated radiation as a seed to improve both the energy and coherent properties of radiation generated by free electron lasers [2], as well as create pulses of attosecond duration [3].
The development of methods for controlling the HHG characteristics is carried out both at the microscopic (atomic) [4] and at the macroscopic level of description of the problem [5]. At the same time, various methods of phase and quasi-phase matching during the propagation of laser radiation in a medium are considered [6]. Within the current study, a unified theoretical approach is used to describe the HHG phenomenon, which takes into account the dynamics of changes in the atomic discrete and continuous spectra levels populations of atoms distributed in the medium during their interaction with intense laser fields, the parameters of which depend on the position of atoms in the medium due to the effects of laser propagation radiation. The single atom response description of the laser fields action is realized by using a unique non-perturbative theoretical approach [7]. The response of an extended medium is simulated within the framework of the interference model [8]. Using the non-perturbative theory and interference model, a series of numerical studies of the effects associated with the generation of coherent radiation when exposed to intense laser radiation on media representing both a single gas jet (to study the effects of phase matching) and a set of gas jets separated by vacuum intervals (to study the features of quasi-phase matching) have been carried out. We recently presented a study of the influence of interaction parameters (medium parameters and laser radiation wavelength) on the HHG efficiency [9]. In the present studies, the emphasis was placed on studying the polarization characteristics of the generated harmonics when varying the interaction parameters. The main results of the studies are presented and discussed. In particular, we have shown that varying the initial time delay between pulses allows one to effectively control the amount of ellipticity of harmonics generated under quasi-phase matching conditions.
The conducted series of studies opens up broad prospects for using the HHG effect in creating compact multispectral sources of coherent arbitrarily polarized radiation.
The study was supported by the Russian Science Foundation (Grant № 24-22-00188).
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[7] A.V. Andreev, S.Yu. Stremoukhov, O.A. Shoutova, Light-induced anisotropy of atomic response: prospects for emission spectrum control. Eur. Phys. J. D. 66.16 (2012).
[8] S.Yu. Stremoukhov and A.V. Andreev, Quantum-mechanical elaboration for the description of low- and high-order harmonics generated by extended gas media: prospects to the efficiency enhancement in spatially modulated media, Las. Phys. 28, 035403 (2018).
[9] S.Stremoukhov, Role of gas pressure in quasi-phase matching in high harmonics driven by two-color laser field, Atoms, 11, 103 (2023).
