New laser sensor detects molecular composition of any gas sample

New laser sensor detects molecular composition of any gas sample
by Clarence Oxford
Los Angeles CA (SPX) Feb 20, 2025

A research team from JILA, a joint institute of CU Boulder and the National Institute of Standards and Technology (NIST), has developed an innovative laser-based sensor capable of analyzing any gas sample and detecting a vast array of molecular components at extremely low concentrations. The new technique, detailed in a study published in *Nature* on Feb. 19, could revolutionize applications ranging from medical diagnostics to environmental monitoring.

The sensor employs a technology called Modulated Ringdown Comb Interferometry (MRCI), which enhances traditional laser absorption methods to detect molecules at parts-per-trillion sensitivity levels. This advancement enables researchers to quickly and cost-effectively analyze gas compositions in various real-world scenarios, including detecting disease biomarkers in human breath and measuring industrial greenhouse gas emissions.

"Even today I still find it unbelievable that the most capable sensing tool can in fact be built with such simplicity, using only mature technical ingredients but tied together with a clever computation algorithm," said lead author Qizhong Liang, a doctoral student at JILA.

Expanding the Scope of Molecular Detection

The new sensor builds on nearly three decades of research in quantum physics at CU Boulder and NIST, leveraging specialized frequency comb lasers. These lasers, originally developed for optical atomic clocks, emit pulses of light in thousands to millions of different wavelengths simultaneously, making them exceptionally suited for molecular detection.

"The frequency comb laser was originally invented for optical atomic clocks, but very early on, we identified its powerful application for molecular sensing," explained Jun Ye, senior author of the study and a fellow at JILA and NIST. "Still, it took us 20 years to mature this technique, finally allowing universal applicability for molecular sensing."

Innovative Optical Cavity Design

The detection process relies on the principle that gases absorb specific optical frequencies in a unique pattern, akin to a fingerprint. Previous methods required laser beams to travel over long distances to achieve high sensitivity, but the new approach confines the gas within an optical cavity-a chamber lined with highly reflective mirrors-where laser light bounces thousands of times, effectively increasing the path length and improving molecular detection.

Earlier optical cavity designs faced limitations due to narrow spectral ranges, restricting the variety of detectable molecules. MRCI overcomes this by dynamically adjusting the cavity size, allowing it to accommodate a broader spectrum of light and significantly enhancing its detection capabilities. By employing sophisticated computational algorithms, the researchers can decode the resulting light patterns to determine the precise chemical composition of the gas sample.

"We can now use mirrors with even larger reflectivity and send in comb light with even broader spectral coverage," Liang said. "But this is just the beginning. Even better sensing performance can be established using MRCI."

Breakthroughs in Medical Diagnostics

One of the most promising applications of MRCI is in medical diagnostics, particularly in analyzing human breath. The team has already demonstrated that the technique can identify microbial activity in the mouth and could eventually assist in diagnosing conditions such as lung cancer, diabetes, and chronic obstructive pulmonary disease (COPD).

"Exhaled breath is one of the most challenging gas samples to be measured, but characterizing its molecular compositions is highly important for its powerful potential for medical diagnostics," said Apoorva Bisht, a co-author of the research and a doctoral student in Ye's lab.

The researchers are collaborating with CU Anschutz Medical Campus and Children's Hospital Colorado to test MRCI on breath samples from children with pneumonia and asthma, as well as from lung cancer patients before and after surgery. These efforts aim to validate MRCI's potential as a non-invasive diagnostic tool for early disease detection.

"It will be tremendously important to validate our approach on real-world human subjects," Ye said. "Through close collaboration with our medical colleagues at CU Anschutz, we are committed to developing the full potential of this technique for medical diagnosis."

Research Report:Modulated ringdown comb interferometry for sensing of highly complex gases