Prospects of designing gold-nanoparticles-based soft terahertz radiation sources and terahertz-to-infrared converters for concealed object detection technology

TL;DR

This paper explores the potential of gold nanobars for generating terahertz radiation and gold nanospheres for terahertz-to-infrared conversion, aiming to improve concealed object detection technology.

Contribution

It introduces a two-phonon scheme in gold nanobars for THz photon generation and assesses design prospects for THz sources and converters for security applications.

Findings

Feasible THz frequencies for security imaging identified

Design considerations for large-area THz sources discussed

Estimates provided for terahertz-to-infrared converters

Abstract

The two-phonon scheme of generation of terahertz (THz) photons by gold nanobars (GNBs) is considered. It is shown that in GNBs, by choosing their sizes, it is possible to provide conditions for converting the energy of longitudinal phonons with THz frequencies into the energy of THz photons. The prospects of designing GNBs-based soft THz radiation sources (frequencies: 0.14; 0.24; 0.41 and 0.70 THz) with a large flow cross-section (diameter ~40 cm) intended for detection of hidden objects under clothing to ensure security in public places (airports, railway stations, stadiums, etc.) are assessed. The choice of the above frequencies is a compromise between the requirements of low absorption of THz radiation by water vapor in air, good penetration through the fabric of clothing, favoring a sufficient resolution of the imaging system, and an abundance of corresponding longitudinal phonons, capable of exciting Fermi electrons in GNBs. Estimates of the characteristics of the terahertz-to-infrared converter based on gold nanospheres (GNSs), which could work in tandem with these sources of THz radiation -- as a means of visualization of hidden objects -- are also given.