A cost-effective laser design that outputs multi-color lasing could improve information flow in optical fibers, and allow multi-color medical imaging of diseased tissue in real time. The laser has been engineered to control the color and intensity of the light by varying the cavity architecture. 

Researchers at Northwestern University demonstrated multi-modal nanolasing using plasmonic superlattices — finite arrays of nanoparticles grouped into microscale arrays — to support multiple band-edge modes capable of multi-modal lasing at programmed emission wavelengths and with large mode spacings. According to the team, access to more than a single band-edge mode for nanolasing was not possible previously because of limitations in cavity designs. 

By modeling the superlattice nanolasers with a four-level gain system and a time-domain approach, researchers showed that the accumulation of population inversion at plasmonic hot spots could be spatially modulated by the diffractive coupling order of the nanoparticle patches. Symmetry-broken superlattices were shown to sustain switchable nanolasing between a single mode and multiple modes. 

Nanoparticle superlattices integrated with liquid gain offer a platform to access different colors with tunable intensities, depending on the geometric parameters of the lattice. 

“In our work, we demonstrated that multi-modal lasing with control over the different colors can be achieved in a single device,” said professor Teri W. Odom. “Compared to traditional lasers, our work is unprecedented for its stable multi-modal nanoscale lasing and our ability to achieve detailed and fine control over the lasing beams.” 

The research provides a strategy for eliminating costly fabrication processes and directly producing multiple, stable lasing peaks from a single device. Currently, multi-color lasing output is only possible by putting together many single-color lasers. 

“In humans, our perception of the world would be limited if we only ‘saw’ in a single color,” Odom said. “Multiple colors are essential for us to receive and process information at the same time, and in the same way, multi-color lasers have the potential for tremendous benefits in daily life.” 

In the future, Odom said she and her team would be interested in designing white nanolasers by covering blue, green and red wavelengths simultaneously, and changing the “whiteness” by controlling the relative intensity of the blue, green, red channels. 

The research could open possibilities for ultra-sensitive sensing in chemical processes, where different molecules could be monitored simultaneously; and in-situ cellular imaging at multiple colors, where different dye labels could be excited by different laser colors correlating to different biological processes. 

The research was published in Nature Nanotechnology (doi: 10.1038/nnano.2017.126).