Ultra-Broadband Visible and Infrared Light Generation Driven by Far Infrared Light in the Broad Region from 8{\mu}m to 240{\mu}m

TL;DR

This study explores broad-spectrum white-light generation using $(PhSn)_4S_6$ molecules excited by mid- and far-infrared radiation, revealing the role of electron and molecular vibrations in the process and highlighting potential applications.

Contribution

It demonstrates white-light generation in $(PhSn)_4S_6$ molecules across 8 to 240 μm wavelengths and analyzes the excitation mechanisms, advancing understanding of nonlinear optical processes in these materials.

Findings

White light generated between 8 and 240 μm excitation wavelengths.

Efficiency depends on whether molecular vibrations are excited.

Electron system and molecular backbone are largely decoupled.

Abstract

The most commonly used nonlinear optical process is the conversion of infrared light at 1064nm to green light at 532nm, as performed in common laser pointers. However, more relevant for future applications are nonlinear optical processes that generate a broad spectrum, a so called supercontinuum. A desirable goal is generating a spectrum that covers the whole visible range (400 -900nm), i.e., white light. Nowadays, white-light generation is usually achieved in specially designed photonic fibres requiring high laser intensities. However, in previous studies we showed that amorphous powders of $(PhSn)_4S_6$ cluster-molecules generate white light when they are irradiated by low-intensity near-infrared light. In this study, we use the mid- and far-infrared radiation of a free-electron laser to investigate the same molecules. White-light generation is observed for excitation with wavelength between 8 and 240$\mu$ m. While the emitted radiation shows only slight variations, its intensity strongly depends on the excitation wavelength. We then match the wavelength dependent efficiency with the infrared absorption spectra of the material. This comparison shows: whenever the excitation can introduce molecular vibrations, less white light is generated. For all other wavelengths the excitation interacts mostly with the electron system. This shows that the electron system and the molecular backbone are decoupled to a large extent. Our work contributes to the understanding of the nonlinear process that underlies white-light generation in $(PhSn)_4S_6$ cluster molecules. Additionally, it shows the high potential of this material in applications where a broad laser spectrum is desired.