Carrier-wave Rabi flopping signatures in high-order harmonic generation for alkali atoms

TL;DR

This paper theoretically investigates carrier-wave Rabi flopping in alkali atoms during high-order harmonic generation, revealing unique spectral features and breakdown of the area theorem in sodium and potassium atoms.

Contribution

It is the first to simulate and analyze carrier-wave Rabi flopping signatures in real atoms via HHG, highlighting new phenomena in alkali species.

Findings

Characteristic peak at 2π pulse area in Na correlates with Rabi flopping.

Complex harmonic structures indicate carrier-wave Rabi flopping at larger pulse areas.

Breakdown of the area theorem observed in K atoms.

Abstract

We present the first theoretical investigation of carrier-wave Rabi flopping in real atoms by employing numerical simulations of high-order harmonic generation (HHG) in alkali species. Given the short HHG cutoff, related to the low saturation intensity, we concentrate on the features of the third harmonic of sodium (Na) and potassium (K) atoms. For pulse areas of 2$\pi$ and Na atoms, a characteristic unique peak appears, which, after analyzing the ground state population, we correlate with the conventional Rabi flopping. On the other hand, for larger pulse areas, carrier-wave Rabi flopping occurs, and is associated with a more complex structure in the third harmonic. These new characteristics observed in K atoms indicate the breakdown of the area theorem, as was already demonstrated under similar circumstances in narrow band gap semiconductors.