# Terahertz cascades from nanoparticles

## TL;DR

This paper proposes a nanoparticle-based system that generates terahertz radiation with quantum yields above unity by engineering radial material composition to produce equidistant energy levels, enabling efficient THz photon emission.

## Contribution

It introduces a novel nanoparticle design with tailored radial composition to achieve high quantum yield THz radiation, including a practical multishell configuration.

## Key findings

- High quantum yield THz radiation achieved
- Design methodology for continuous composition profiles
- Experimental feasibility of multishell nanoparticles

## Abstract

In this article we propose a system capable of THz radiation with quantum yield above unity. The system consists of nanoparticles where the material composition varies along the radial direction of each nanoparticle in such a way that a ladder of equidistant energy levels emerges. By then exciting the highest level of this ladder we produce multiple photons of the same frequency in the THz range. We demonstrate how we can calculate a continuous material composition profile that achieves a high quantum yield and then show that a more experimentally friendly design of a multishell nanoparticle can still result in a high quantum yield.