NASA's quarter-size lasers can be our best shot to find water on the Moon

In January of 2022, China's space program (CNSA) was the first to detect water signals directly from the Moon's surface thanks to its Chang'e-5 lunar probe. Since then, space explorers have been on the hunt for more such signals.

Indeed water on the moon could make the celestial object habitable and further inspire future missions. But finding this water is easier said than done.

Confirming the existence of water on the moon

“Previous experiments inferred, then confirmed the existence of small amounts of water across the Moon. However, most technologies do not distinguish among water, free hydrogen ions, and hydroxyl, as the broadband detectors used cannot distinguish between the different volatiles,” said NASA in a statement.

That’s why Goddard engineer Dr. Berhanu Bulcha has been working on a type of instrument called a heterodyne spectrometer that could zoom in on particular frequencies to definitively identify and locate water sources on the Moon. To function however, it would need a stable, high-powered, terahertz laser, which was prototyped in collaboration with Longwave Photonics through NASA’s Small Business Innovation Research (SBIR) program.

“This laser allows us to open a new window to study this frequency spectrum,” Bulcha said. “Other missions found hydration on the Moon, but that could indicate hydroxyl or water. If it’s water, where did it come from? Is it indigenous to the formation of the Moon, or did it arrive later by comet impacts? How much water is there? We need to answer these questions because water is critical for survival and can be used to make fuel for further exploration.”

The new tool would function by detecting spectra or wavelengths of light in order to reveal the chemical properties of matter that light has touched. Hydrogen-containing compounds like water emit photons in the terahertz frequency range (2 trillion to 10 trillion cycles per second) between microwave and infrared. This means that scientists can measure the difference between a laser source and the combined wavelength to identify water molecules.

“The problem with existing laser technology,” Bulcha said, “is that no materials have the right properties to produce a terahertz wave.”

Quantum cascade lasers

To resolve this issue, Bulcha’s team is developing quantum cascade lasers that produce photons from each electron transition event. In these materials, a laser emits photons in a specific frequency and creates a cascade of terahertz-energy photons. This cascade consumes less voltage to generate a stable, high-powered light.

There is still one issue with this technology and that is that its beam spreads out in a large angle, dissipating quickly over short distances. Bulcha addressed this drawback by integrating the laser on a waveguide with a thin optical antenna to tighten the beam. The integrated laser and waveguide unit reduces this dissipation by 50% in a package smaller than a quarter.

He now hopes to have his new super efficient lasers ready for NASA’s Artemis program. The device is small and compact enough to fit in a CubeSat making it ideal for this mission. Will it be the key to finding water on the moon? Only time will tell.

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