Compact Laser Detects Greenhouse Gases Using Mid-IR Source

A system developed at École Polytechnique Fédérale de Lausanne (EPFL), composed of a standard laser and a photonic chip, uses a mid-infrared light source to detect greenhouse and other gases. The team took a commercially available fiber laser and combined it with a waveguide chip to reliably generate lightwaves in the MIR spectrum.

Researchers at EPFL have come up with a new MIR light source that can detect greenhouse and other gases, as well as molecules in a person’s breath. Courtesy of Alain Herzog/EPFL.

The fiber laser emits light in a specific wavelength range. The beam is directed through a waveguide measuring 1 μm (0.001 mm) across and one-half mm in length. The waveguide can alter the frequency of the light as it passes through. The researchers refined key aspects of the system’s design, including the waveguide geometry and material and the wavelength of the original laser source, to develop a system that is simple, yet efficient and sturdy. The team can tune the wavelength of the light by adjusting the waveguide’s geometry.

This turnkey, highly efficient, compact MIR source offers power levels sufficient for spectroscopy application. As a proof of principle, the team used the system for detection of acetylene, a colorless and highly flammable gas, by absorption spectroscopy.

Detecting pollution with a compact laser source. (l) to (r): Eirini Tagkoudi, Camille Brès, and Davide Grassani. Courtesy of Alain Herzog/EPFL.

The system produces light in the MIR spectrum, retaining 30% of the original signal strength. In experiments the team demonstrated that waveguides pumped with a 2-μm fs-fiber laser can reach a spectroscopic spectral region in the 3- to 4-μm range, with up to 35% power conversion and mW-level output powers.

“This device sets a new benchmark for efficiency,” said researcher Davide Grassani. “This is the first time anyone has created a fully integrated spectroscopic laser source. It does away with the painstaking process of precisely aligning all the parts in a conventional laser system.”

Until now, IR laser systems have been difficult to transport for use because they involve complex, damage-prone hardware. This advancement could lead to additional miniaturized MIR technologies — a wavelength range that scientists rarely get to work with. “Once we’ve developed the system further, we could well see on-chip detectors that scientists can easily carry out into the field,” said Camille Brès, professor and head of the Photonic Systems Laboratory.

The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-09590-3).