Plasmonic nanolaser can be stretched to different wavelengths

June 22, 2018 // By Julien Happich
Inspired from the chameleons' ability to change their skin colour by controlling the spacing among nanocrystals, which determine locally the skin's structural colour, researchers from the Northwestern University of Illinois have elaborated a plasmonic nanolasing system whose wavelength can be continuously tuned as the system is stretched, moving the arrayed nanoparticles apart from each other.

The results published in the Nano Letters journal under the title "Stretchable Nanolasing from Hybrid Quadrupole Plasmons" is a continuation of previous work when the researchers had demonstrated nanolasing from coupled arrays of metal nanoparticles (NPs) surrounded by a gain media. Since they had observed that lasing wavelengths could be tailored by varying the refractive index of the environment and the NPs' lattice spacing, they opted to fabricate arrays of cylindrical gold nanoparticles (260nm in diameter and 600nm apart) on a stretchable substrate that would allow a reconfigurable, mechanical control over the lattice's spacing (and the plasmonic nanocavity modes). In order to maintain homogeneity and the same dye concentration of the lasing medium around the nanoparticles, the researchers used a liquid dye which would flow freely within the array as the polymer (PDMS) substrate was stretched.

Pumped optically, the large metal NPs produced hybrid quadrupole lattice plasmons (HQLs) with sharp resonances under different strains. In their paper, the authors report that stretching the device along the polarization direction results in out-of-plane standing waves at the band edge that are tolerant to lateral changes in lattice spacing, yielding reversibly tuneable nanolasing.

Experimentally, they demonstrated that wavelength tuning was ultrasensitive to strain, with a wavelength shift of 31nm for a 0.03 strain variation. In effect and in accordance to their theoretical models, changing the inter-particle distances directly modulated the cavity resonance, reversibly as the substrate was stretched and released.

The researchers note that by construction, their stretchable laser can easily accommodate different gain materials such as dye molecules, quantum dots, and 2D materials, which should make it possible to tune the lasing wavelength from UV to near-infrared.

They conclude that such stretchable nanolaser architectures could find their way in flexible photonic devices for in situ biomedical imaging, as well as being used for the mechanical modulation of strong light-matter interactions in fluorescence, photocatalysis, and quantum optics.

Northwestern University of Illinois -  www.northwestern.edu


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