Visible infrared at room temperature achieved in a first

Rohit Chikkaraddy/ University of Birmingham

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A collaborative effort between researchers at the Univerisity of Birmingham and the University of Cambridge in the UK has led to the development of a new method that uses quantum systems to help detect mid-infrared (MIR) light at room temperature, a press release said.

Mid-infrared, as the name suggests, lies between the infrared spectrum's near and far wavelengths, just outside those of visible light. The mid-infrared spectrum has gained particular importance as it has been useful for multiple applications ranging from military to environmental and medical treatments and studying celestial objects.

Detectors used in these devices rely on cooled semiconductors that are not only bulky but also energy-intensive. By making mid-infrared detection possible at room temperature, the researchers have opened up new avenues for research and practical devices in various fields.

When scientists are looking to study structures of chemical and biological molecules, they use mid-infrared light to excite the bonds between the constituent atoms. This makes the bonds vibrate at high frequencies.

While scientists have done this at low temperatures in the past, doing this at room temperature means they also need to account for the random motion seen in bonds, leading to additional thermal noise.

To avoid thermal noise, the research team led by Rohit Chikkaraddy, an assistant professor in physics at the University of Birmingham, assembled molecular emitters into small plasmonic cavities to resonant in MIR and visible ranges.

Called MIR Vibrationally-Assisted Luminescence or MIRVAL, the approach also includes engineering the emitters so that their molecular vibrational states and electronic states could interact and result in an efficient transduction of MIR light into enhanced visible luminescence.

Creating picocavities allows light trapping from the smallest sources, such as single-atom defects in metals. The researchers could also confine the light in extremely small volumes, even below one cubic nanometer, thereby increasing the resolution of the data obtained.

"The most challenging aspect was to bring together three widely different length scales – the visible wavelength, which are hundreds of nanometres, molecular vibrations, which are less than a nanometre, and the mid-infrared wavelengths, which are ten thousand nanometres – into a single platform and combine them effectively,” said Chikkaraddy in a press release.

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The team's breakthrough can help us deepen our understanding of highly complex systems and infrared active molecular vibrations down to the single-molecule level, which has never been achieved before. While this will help researchers study molecules better, it also opens doors to multiple applications as well.

"MIRVAL could have a number of uses such as real-time gas sensing, medical diagnostics, astronomical surveys, and quantum communication, as we can now see the vibrational fingerprint of individual molecules at MIR frequencies," Chikaraddy added.

The ability for room temperature detection will also help ease both applications and further research in the field. Future advances will find their way into devices that can then help us manipulate atoms at a quantum level, the press release said.

The research findings were published today in the journal Nature Photonics.