Nanolaser Could Function inside Living Tissue

These nanolasers can effectively deliver visible laser light at penetration depths accessible to longer wavelengths. (Source: NWU)

Researchers have developed a tiny nanolaser that can function inside of living tissues without harming them. Just 50 to 150 nanometers thick, the laser can fit and function inside living tissues, with the potential to sense disease biomarkers or perhaps treat deep-brain neuro­logical disorders, such as epilepsy. Developed by researchers at North­western and Columbia Universities, the nanolaser shows specific promise for imaging in living tissues. Not only is it made mostly of glass, which is intrinsi­cally bio­compatible, the laser can also be excited with longer wave­lengths of light and emit at shorter wavelengths.

“Longer wavelengths of light are needed for bio­imaging because they can penetrate farther into tissues than visible wave­length photons,” said Teri Odom, who co-led the research. “But shorter wavelengths of light are often desirable at those same deep areas. We have designed an optically clean system that can effec­tively deliver visible laser light at pene­tration depths accessible to longer wavelengths.” The nanolaser also can operate in extremely confined spaces, including quantum circuits and micro­processors for ultra-fast and low-power electronics. Odom co-led the work with P. James Schuck at Columbia University’s School of Engi­neering.

While many applications require increa­singly small lasers, researchers continually run into the same roadblock: Nanolasers tend to be much less efficient than their macr­oscopic counte­rparts. And these lasers typically need shorter wavelengths, such as ultraviolet light, to power them. “This is bad because the uncon­ventional environ­ments in which people want to use small lasers are highly susceptible to damage from UV light and the excess heat generated by ineffi­cient operation,” said Schuck.

Odom, Schuck and their teams were able to achieve a nanolaser platform that solves these issues by using photon upcon­version. In upcon­version, low-energy photons are absorbed and converted into one photon with higher energy. In this project, the team started with low-energy, bio-friendly infrared photons and upcon­verted them to visible laser beams. The resulting laser can function under low powers and is vertically much smaller than the wavelength of light.

“Our nanolaser is transparent but can generate visible photons when optically pumped with light our eyes cannot see,” said Odom. “The continuous wave, low-power charac­teristics will open numerous new appli­cations, especially in biological imaging.” “Exci­tingly, our tiny lasers operate at powers that are orders of magni­tude smaller than observed in any existing lasers,” Schuck said. (Source: NWU)

Reference: A. Fernandez-Bravo et al.: Ultralow-threshold, continuous-wave upconverting lasing from subwavelength plasmons, Nat. Mat., online 23 September 2019; DOI: 10.1038/s41563-019-0482-5

Link: Group T. Odom, Dept. of Materials Science and Engineering, Northwestern University, Evanston, USA

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