High-order harmonic generation by aligned heteronuclear diatomic molecules in an orthogonally polarized two-color laser field

Dino Habibović; Wilhelm Becker; Dejan B. Milošević

doi:10.1140/epjd/s10053-021-00133-4

2024 Impact factor 1.5

Atomic, Molecular, Optical and Plasma Physics

Quantum Aspects of Attoscience

Eur. Phys. J. D (2021) 75: 122
https://doi.org/10.1140/epjd/s10053-021-00133-4

Regular Article - Ultraintense and Ultrashort Laser Fields

High-order harmonic generation by aligned heteronuclear diatomic molecules in an orthogonally polarized two-color laser field

Dino Habibović¹, Wilhelm Becker²^,3 and Dejan B. Milošević¹^,2^,4^c

¹ Faculty of Science, University of Sarajevo, Zmaja od Bosne 35, 71000, Sarajevo, Bosnia and Herzegovina
² Max-Born-Institut for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2a, 12489, Berlin, Germany
³ National Research Nuclear University MEPhI, Kashirskoe Shosse 31, 115409, Moscow, Russia
⁴ Academy of Sciences and Arts of Bosnia and Herzegovina, Bistrik 7, 71000, Sarajevo, Bosnia and Herzegovina

^c milo@bih.net.ba

Received: 7 January 2021
Accepted: 24 March 2021
Published online: 9 April 2021

Abstract

Using the molecular strong-field approximation, we investigate high-order harmonic generation by heteronuclear diatomic molecules exposed to an orthogonally polarized two-color laser field, which consists of two mutually orthogonal linearly polarized fields with frequencies $r ω$ $r\omega$ and $s ω$ $s\omega$ . Here, r and s are integers and $ω$ $\omega$ is the fundamental frequency. The harmonic emission rate and the harmonic ellipticity can be controlled using the laser-field parameters, in particular the relative phase and the intensity ratio of the laser-field components. The value of the relative phase, for which the emission rate is optimal, and the position of the cutoff can be estimated using a classical model. Also, we analyze the harmonic emission rate and the harmonic ellipticity as functions of the molecular orientation, which can also be used as a control parameter. Two types of minima are present in the spectra, depending on r and s. For $r + s$ $$r+s$$ even, interference minima are present in the spectra of the T-matrix component either parallel or perpendicular to the internuclear axis. Using quantum-orbit theory and the saddle-point method, we derive a condition for the interference minima, which relates the molecular orientation angle $θ_{L}$ $\theta _L$ and the harmonic order n. The corresponding curves in the ( $θ_{L}$ $\theta _L$ , n) plane well reproduce the minima of the numerically calculated spectra. For $r + s$ $$r+s$$ odd, minima are present in the spectra for a particular molecular orientation angle. These minima are explained using the explicit form of the T-matrix element. A heteronuclear as opposed to a homonuclear molecule affords a larger region in the parameter space where both the harmonic ellipticity and the harmonic intensity vary smoothly and both are large.