The new method makes infrared light visible at room temperature

Quantum-derived discoveries could significantly simplify the detection of mid-infrared light at room temperature.

Researchers from the University of Birmingham and the University of Cambridge have unveiled a groundbreaking technique that allows them to detect mid-infrared (MIR) light at room temperature using quantum systems.

Published in Natural PhotonicsThe research was carried out at Cambridge’s Cavendish Laboratory and represents a major advance in scientists’ ability to gain insight into the functioning of chemical and biological molecules.

In a new method using quantum systems, the team converted low-energy MIR photons into high-energy visible photons using molecular emitters. The new discovery has the potential to help scientists detect the MIR and perform spectroscopy at the single-molecule scale at room temperature.

Dr. Rohit Sikarati, Assistant Professor University of Birminghamand the lead author of the study explained: „The bonds that maintain the distance between atoms in molecules vibrate like springs, and these vibrations resonate at very high frequencies. These springs can be excited by light in the mid-infrared region, invisible to the human eye. At room temperature, these springs are in random motion, i.e. mid-infrared. A major challenge in detecting light is avoiding this thermal noise. Modern detectors rely on power-intensive and bulky cooled semiconductor devices, but our research presents a new and exciting way to detect this light at room temperature.

The new approach is called MIR resonance-assisted luminescence (MIRVAL) and uses molecules capable of absorbing both MIR and visible light. The team was able to incorporate molecular emitters into a very small plasmonic cavity that resonates in both the MIR and visible ranges. They further designed it so that the molecular vibrational states and electronic states can interact, resulting in efficient transmission of MIR light for enhanced fluorescence.

Dr. Ciccarati continued: „The most challenging aspect is to bring together three vastly different length scales – visible wavelengths of hundreds of nanometers, molecular resonances of less than a nanometer and mid-infrared wavelengths of tens of nanometers – and combine them effectively on a single platform.”

By creating picocavities, incredibly small cavities that trap light and form single-al.Atomic Defects in metallic features have enabled researchers to achieve extreme light blocking levels below one cubic nanometer. This means the team can control MIR light down to the size of a single molecule.

This advance has the potential to deepen the understanding of complex systems and opens the gateway to infrared-active molecular resonances that are normally inaccessible at the single-molecule level. But beyond pure scientific research, MIRVAL is useful in many fields.

Dr. Ciccaradi concluded: “MIRVAL could have many applications such as real-time gas sensing, medical diagnostics, astronomical studies and quantum communication, as we can now observe the vibrational fingerprint of individual molecules at MIR frequencies. The ability to detect MIR at room temperature makes it much easier to explore these applications and conduct further research in this field. With further developments, this novel method will not only enter practical devices shaping the future of MIR technologies, but also open up the ability to coherently manipulate the complex interaction of atoms in 'springs with balls’ in molecular quantum systems.

Reference: Rohit Sikarati, Rakesh Arul, Lucas A. Jacob and Jeremy J. Bamberg, 28 August 2023, “Single-Molecule Mid-Infrared Spectroscopy and Detection by Vibrational-Assisted Luminescence” Natural Photonics.
DOI: 10.1038/s41566-023-01263-4