Measuring light: the world’s most accurate ruler

A portable laser device that tests your breath for signs of disease and organ failure is just the start of the University of Adelaide’s ambitions for laser technology.

Light is knowledge. Even these words are revealed to you by light. What kinds of knowledge could we reveal if we could measure light itself? As it turns out, a lot.

The Optical Frequency Comb measures light with extreme precision, and its range of applications may surprise you. For example, it already manages greenhouse gases being released by mines and farms and measures the colour of distant stars to detect planets orbiting them. Unfortunately, today’s light-measuring devices are big, complex, and expensive, limiting their practical use. Fortunately, the University of Adelaide and its partners are hard at work making the technology much more practical, while at the same time exploring its limitless potential.

Researchers at Adelaide University’s Institute for Photonics and Advanced Sensing (IPAS) have joined the ARC Centre of Excellence in Optical Microcombs for Breakthrough Science (COMBS) to make these tools much smaller and much cheaper and explore how these ‘microcombs’ can really change the world.  A major advancement led by IPAS is an instrument to diagnose medical conditions from the human breath. 

‘Frequency combs produce many different coloured lasers,’ explains lead researcher Dr Sarah Scholten. ‘The lasers can interact with and be absorbed by gas molecules.’

Each human breath holds hundreds of such molecules, which in turn hold information about our health.

‘By looking at the colours these interactions produce and at the amount of light absorbed, analysts can identify what molecules are present, and how many. In real time, they can monitor the volatile organic compounds that indicate organ failure and disease.’

To test their prototype, the team turned to baker’s yeast.

‘Like humans,’ says Dr Christopher Perrella, another lead researcher, ‘baker’s yeast produces carbon dioxide as it “breathes”, and the composition of its emission changes with its diet and environment.’

The team was successful. Their prototype distinguished between different isotopes of carbon dioxide and monitored carbon dioxide production in real time. This marks the first time that optical frequency combs have effectively observed the changing metabolism of a living organism in real time—all by measuring light.

‘This holds the potential to revolutionise the simplicity, speed, and efficiency of health assessments. It is a pivotal moment in health innovation,’ Dr Scholten says. 

‘As our understanding of breath analysis improves, we might look forward to a day when blood tests are replaced with breath tests.’

What’s next?

Researchers believe this technology has the potential to be more cost-effective, more user-friendly, and more portable. In 1945, a digital computer weighed about 30,000 kilograms; in 2024, we wear digital computers on our wrists. The University of Adelaide, one of eight universities in COMBS, is working make our light-measuring devices as small as a fingernail. The goal is to continuously increase accessibility, bringing real-time assessment to even the most remote of places.

Measuring the light of atoms, we can keep time. Measuring the light of distant stars, we can find exoplanets. Measuring light’s interaction with gas molecules, we can detect greenhouse gases. The microcomb even transmits information, giving us record-breaking internet speeds. It has been called the world’s most accurate ruler. If we develop it as successfully as we developed the digital computer, there is no telling where we will go.