Cascaded Parametric Amplification for Highly Efficient Terahertz Generation

TL;DR

This paper introduces a cascaded optical parametric amplification method for efficient terahertz generation, achieving over 8% energy conversion efficiency by leveraging exponential energy growth through cascaded down-conversion.

Contribution

It presents a novel cascaded amplification approach for terahertz generation that surpasses quantum-defect efficiency and accounts for complex nonlinear interactions and phase-matching conditions.

Findings

Predicted >8% energy conversion efficiency for 100 ps pulses.

Demonstrated exponential growth of THz energy via cascaded process.

Analyzed distinct physics of coupled nonlinear interactions in THz-COPA.

Abstract

A highly efficient, practical approach to high-energy terahertz (THz) generation based on spectrally cascaded optical parametric amplification (THz-COPA) is introduced. The THz wave initially generated by difference frequency generation between a strong narrowband optical pump and optical seed (0.1-10% of pump energy) kick-starts a repeated or cascaded energy down-conversion of pump photons. This helps to greatly surpass the quantum-defect efficiency and results in exponential growth of THz energy over crystal length. In cryogenically cooled periodically poled lithium niobate, energy conversion efficiencies >8% for 100 ps pulses are predicted. The calculations account for cascading effects, absorption, dispersion and laser-induced damage. Due to the coupled nonlinear interaction of multiple triplets of waves, THz-COPA exhibits physics distinct from conventional three-wave mixing parametric amplifiers. This in turn governs optimal phase-matching conditions, evolution of optical spectra as well as limitations of the nonlinear process.