Multicycle terahertz pulse generation by optical rectification in LiNbO$_3$, LiTaO$_3$, and BBO crystals

TL;DR

This paper demonstrates enhanced multicycle terahertz pulse generation at around 14 THz in LiNbO$_3$, LiTaO$_3$, and BBO crystals through phase-matched optical rectification, with a novel resonance effect linked to the Pockels effect.

Contribution

It reveals a resonant cascading mechanism involving the Pockels effect that significantly boosts terahertz generation efficiency when using chirped laser pulses.

Findings

Enhanced terahertz energy with highly chirped pulses in LiNbO$_3$

Observation of multicycle terahertz emission in LiTaO$_3$ and BBO

Identification of a Pockels effect-driven resonance increasing conversion efficiency

Abstract

We report multicycle, narrowband, terahertz radiation at 14.8 THz produced by phase-matched optical rectification of femtosecond laser pulses in bulk lithium niobate (LiNbO$_3$) crystals. Our experiment and simulation show that the output terahertz energy greatly enhances when the input laser pulse is highly chirped, contrary to a common optical rectification process. We find this abnormal behavior is attributed to a linear electro-optic (or Pockels) effect, in which the laser pulse propagating in LiNbO$_3$ is modulated by the terahertz field it produces, and this in turn drives optical rectification more effectively to produce the terahertz field. This resonant cascading effect can greatly increase terahertz conversion efficiencies when the input laser pulse is properly pre-chirped with additional third order dispersion. We also observe similar multicycle terahertz emission from lithium tantalate (LiTaO$_3$) at 14 THz and barium borate (BBO) at 7 THz, 10.6 THz, and 14.6 THz, all produced by narrowband phase-matched optical rectification.