This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers at the University of Eastern Finland have uncovered two complementary mechanisms that govern coherence in miniaturized lasers composed of metallic nanoparticle arrays incorporated into an optical gain material, also known as plasmonic lattice lasers. In one study, published in Laser & Photonics Reviews, they showed that these nanostructures can generate phase-locked ultrafast laser pulse modulation through the synchronization of multiple lasing modes.
In a second study, published in ACS Nano, they demonstrated that structures supporting lasing modes with different topologies and polarizations can sustain independent channels without mutual coherence. Together, these findings establish a unified physical picture of coherence formation in plasmonic lasers and provide new design principles for nanoscale photonic devices. The studies also connect plasmonic nanolasing with concepts from topological photonics, a field that applies ideas from topology, a branch of mathematics that describes properties that remain robust against small perturbations.
Previously, topology in physics has been used to generate exotic topological phases of matter (David Thouless, Duncan Haldane and Michael Kosterlitz, 2016 Nobel Prize in Physics). In photonic systems, topology provides a way to generate unidirectional propagation of light similar to electrical diodes and to classify lasing modes into distinct categories, including topologically trivial and nontrivial states. The studies reveal how the topology and polarization of lasing modes can influence whether different modes synchronize or remain independent.
The work advances the fundamental understanding of plasmonic lasing and opens new opportunities for applications ranging from chip-scale ultrafast light sources to low-crosstalk photonic technologies. In the Laser & Photonics Reviews paper, the researchers demonstrated that plasmonic superlattices (i.e., lattices composed of two or more periodicities) supporting topologically trivial lasing modes can generate mode-locked ultrafast laser pulse modulation. When combining the nanoparticle lattice with a liquid dye gain medium and optical pumping, two lasing modes became phase-locked through near-field interactions, leading to ultrafast pulse modulation.
"A major challenge was developing a measurement setup capable of resolving these ultrafast dynamics," says doctoral researcher Janne Heikkinen, lead author of the study. "Once we achieved this, we could directly observe how different lasing modes synchronize to produce ultrafast modulation." Numerical simulations revealed the physical origin of the phase locking. The calculations showed that femtosecond-scale correlations emerge within the shared gain medium at plasmonic hotspots, providing a mechanism that synchronizes the lasing modes.
"The simulations allowed us to study the gain dynamics and identify the origin of the phase correlations," says postdoctoral researcher Roman Calpe. "We found that correlations formed at the plasmonic electric field hotspots around the nanoparticles enabled phase locking between multiple lasing modes." Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly. The second study in ACS Nano revealed fundamentally different behavior when the lasing occurred in modes belonging to different topological classes.
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