# Terahertz continuum generation in the LCS lattice

## TL;DR

This paper explores how extending Rabi oscillation theory to a three-level Dirac system with a flat band enhances nonlinear terahertz continuum generation, revealing new effects beyond traditional models.

## Contribution

It introduces a novel three-level Dirac system model with a flat band, demonstrating enhanced Rabi effects and terahertz continuum generation not captured by previous theories.

## Key findings

- Enhanced Rabi oscillations due to flat band coupling
- Significant increase in terahertz continuum generation
- Potential for new nonlinear optical applications

## Abstract

Rabi oscillations in two-level Dirac systems have been shown to alter the frequency content of the system's nonlinear response. In particular, when considering Rabi oscillations in a quantum model beyond the semiclassical Boltzmann theory, even harmonics may be generated despite the centrosymmetric nature of these systems. This effect magnifies with increasing excitation intensity. In this work, we extend the Rabi theory to a three-level Dirac system arising from a line-centered-square optical lattice. In this case, the Dirac cones are bisected at the Dirac point by a flat band that persists throughout the Brillioun zone. Due to the presence of this flat band, we expect a significant enhancement of the coupling between Dirac states, resulting in a large increase of the Rabi effects and the associated nonlinearities, leading to continuum generation of terahertz radiation.