Prospects of odd and even harmonics generation by an atom in high-intensity laser field

TL;DR

This paper investigates harmonic generation in atoms under high-intensity laser fields, revealing that both odd and even harmonics can be emitted, especially in strong fields, challenging semiclassical models.

Contribution

It introduces a quantum approach to analyze harmonic generation, demonstrating the emergence of even harmonics and limitations of semiclassical methods in strong fields.

Findings

Both odd and even harmonics can be generated at high laser intensities.

Semiclassical approaches are inadequate in the strong-field regime.

Even harmonics originate from quantum effects beyond perturbation theory.

Abstract

New approach to study the spontaneous emission of the atomic system in the presence of the high-intensity laser field is used to study the process of harmonic generation. The analysis is based on the consideration of quantum system interaction with quantized field modes beeing in vacuum state, while the intense laser field is considered classically beyond the perturbation theory. The numerical analysis of the emission from the single one-electron one dimensional atom irradiated by the femtosecond laser pulse of Ti-Sa laser is discussed. It is demonstrated that not only odd but also even harmonics can be emitted if the laser field is strong enough. The origin of appearance of even harmonics is studied. The obtained results are compared with that found in the frames of semiclassical approach widely used to study the harmonic generation. It is found that semiclassical approach is inapplicable in the strong-field limit.