Silver nanocubes form miniature laser
Researchers in Lithuania have developed a nanolaser constructed from a series of silver nanocubes without the need for accurate alignment.
Working with a partner n Japan, the researchers at the Kaunas University of Technology (KTU) developed the nanolaser with the silver nanocubes arranged on a surface and filled with an optically active material. This creates the mechanism needed to amplify light and produce the laser effect.
The design has applications in early medical diagnostics, data communication, and security technologies
“Nanolasers are lasers that use structures a million times smaller than a millimetre to generate and amplify light, and the laser radiation is generated in an extremely tiny volume of material,” says Dr Mindaugas Juodėnas, researcher at the KTU Institute of Materials Science.
“The silver nanocubes are extremely small, monocrystalline silver particles with excellent optical properties. It is an essential part of the nanolaser we have developed.”
The nanocubes are synthesised using a unique process invented by KTU partners in Japan, ensuring their precise shape and quality. These nanocubes are then arranged into a two-dimensional structure using the nanoparticle self-assembly process. During this process, the particles naturally arrange themselves from a liquid medium into a pre-patterned template.
When the template parameters match the optical properties of the nanocubes, a unique phenomenon called surface lattice resonance is created, allowing efficient light generation in an optically active medium.
While conventional lasers use mirrors to produce this phenomenon, the nanolaser uses a surface with nanoparticles instead. “When the silver nanocubes are arranged in a periodic pattern, light gets trapped between them. In a way, the process reminds a hall of mirrors in an amusement park, but in our case, the mirrors are the nanocubes and the visitor of the park is light,” said Juodėnas.
This light accumulates until finally the energy threshold for stimulated emission is crossed. Combined with the laser dye pyrromethene-597, the nanocube array lases at 574 nm with <1.2 nm linewidth, <100 μJ cm−2 lasing threshold, and produces a beam with <1 mrad divergence, despite less-than-perfect arrangement. Such plasmonic nanolasers can be produced on a large-scale and integrated in point-of-care diagnostics, photonic integrated circuits, and optical communications applications.
“Chemically synthesised silver nanocubes can be produced in hundreds of millilitres, while their high quality allows us to use nanoparticle self-assembly technology. Even if their arrangement is not perfect, their properties make up for it,” says Juodėnas.
The nanolaser could be used as a light source in ultra-sensitive biological sensors for early detection of diseases or real-time monitoring of biological processes. It could also be applied in miniature photonic chips, identification technologies, and authentication devices, where the beam’s unique structure is crucial.
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