Frequency-doubled scattering of symmetry-breaking surface-state electrons on liquid Helium

TL;DR

This paper demonstrates frequency doubling of electromagnetic radiation from surface-state electrons on liquid Helium due to symmetry-breaking eigenstates, enabling second harmonic generation in the Terahertz range.

Contribution

It introduces a novel mechanism for second harmonic generation involving Rabi oscillations in surface-state electrons on liquid Helium, extending nonlinear optical effects to Terahertz frequencies.

Findings

Frequency-doubled electromagnetic radiation observed.

Rabi oscillations enable frequency doubling beyond resonance.

Terahertz range radiation produced via symmetry-breaking eigenstates.

Abstract

Any systems with symmetry-breaking eigenstates can effectively radiate photons with doubled frequency of the incident light, which is known as the second harmonic generation. Here, we study the second-order nonlinear effects with the system of surface-state electrons on liquid Helium. Due to the symmetry-breaking eigenstates, we show that a Rabi oscillation between two levels of the surface-state electrons can be realized beyond the usual resonant driving. Consequently, an electromagnetic field with the doubled frequency of the applied driving could be effectively radiated. This can be regarded as a frequency-doubled fluorescence, and interestingly, it works in the unusual Terahertz range.