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Controlling multi-modal nanolasing with plasmonic superlattices

(Nanowerk Spotlight) Lasers are coherent light sources essential in optical communications, checkout counters at retail stores, and computer printing. To ensure stable output at single wavelengths, conventional lasers exploit specific mode-selection rules.
Multi-modal lasers can emit at different wavelengths simultaneously and are important for applications ranging from multiplexed signal processing to multi-color biomedical imaging. To achieve multi-wavelength capabilities, however, the single-color lasers need to be operated as an array of lasers, which dramatically increases the unit cost and precludes their integration with compact photonic devices.
In new work coming out of Teri Odom's lab at Northwestern University, the group demonstrated that multi-modal lasing with control over the different colors can be achieved in a single device.
As the team reports in Nature Nanotechnology ("Band-edge engineering for controlled multi-modal nanolasing in plasmonic superlattices"), nanoparticle superlattices – finite-arrays of metal nanoparticles grouped into microscale arrays – integrated with liquid gain offer a platform to access different colors with tunable intensities depending simply on the geometric parameters of the lattice.
Multi-modal nanolasing was achieved in gold nanoparticle superlattices surrounded by liquid dye solutions
Multi-modal nanolasing was achieved in gold nanoparticle superlattices surrounded by liquid dye solutions. These lasing modes emerge from multiple band-edges at both zero and non-zero wave vectors in the optical band structure. Multiple lasing spots were detected in the far field from the superlattice arrays, and the emission angle of each can be tailored. (Image: Danqing Wang, Odom Group, Northwestern University) (click on image to enlarge)
"In this work, we show how plasmonic gold nanoparticle superlattices enable access to multiple band-edges at zero and non-zero wave vectors that can be exploited for multi-modal lasing with characteristics distinct from traditional photonic and plasmonic lasers," Odom tells Nanowerk. "Compared to traditional lasers, the unprecedented characteristics of these superlattices include stable multi-modal nanoscale lasing and detailed and fine control over lasing beams."
In nanoparticle superlattices, each lasing mode exhibits distinct local electromagnetic field distributions. For example, the field maxima of one mode could be located close to the nanoparticles while another mode could have more field concentration in the region between the particles.
Hence, mode competition for the available gain at overlapped regions is minimized (which is typically a problem for multi-modal lasers, since all the potential colors end up collapsing into a single, dominant color). Multi-modal nanoscale lasing is remarkably stable over a large range of pump powers.
Varying nanoparticle superlattice geometries provides a robust way to manipulate the emission wavelengths, angles at which the light are emitted from the surface, and numbers of multiple lasing beams. Additionally, tuning nanoparticle size can modulate the output intensity of each lasing peak, which is not possible in conventional lasers.
"Our work offers new insights into the design and mechanism of multi-modal nanoscale lasing based on structural engineering and manipulating the optical band structures of nanoparticle superlattices," Odom concludes. "With top-down nanofabrication processes, nanoparticle superlattices can be scaled and integrated with commercial optical devices."
She points out that the generation of multiple stable and tunable lasing wavelengths from a single architecture will greatly improve opto-electronic device efficiencies and could revolutionize cavity designs in laser development.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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