A Northwestern University research team has found a way to manufacture single laser devices that are the size of a virus particle and that operate at room temperature and defy the diffraction limit of light. These plasmonic nanolasers could be readily integrated into silicon-based photonic devices, all-optical circuits and nanoscale biosensors.
Reducing the size of photonic and electronic elements is critical for ultra-fast data processing and ultra-dense information storage. The miniaturization of a key, workhorse instrument — the laser — is no exception.
ABSTRACT – Plasmonic lasers exploit strong electromagnetic field confinement at dimensions well below the diffraction limit. However, lasing from an electromagnetic hot spot supported by discrete, coupled metal nanoparticles (NPs) has not been explicitly demonstrated to date. We present a new design for a room-temperature nanolaser based on three-dimensional (3D) Au bowtie NPs supported by an organic gain material. The extreme field compression, and thus ultrasmall mode volume, within the bowtie gaps produced laser oscillations at the localized plasmon resonance gap mode of the 3D bowties. Transient absorption measurements confirmed ultrafast resonant energy transfer between photoexcited dye molecules and gap plasmons on the picosecond time scale. These plasmonic nanolasers are anticipated to be readily integrated into Si-based photonic devices, all-optical circuits, and nanoscale biosensors.
“Coherent light sources at the nanometer scale are important not only for exploring phenomena in small dimensions but also for realizing optical devices with sizes that can beat the diffraction limit of light,” said Teri Odom, a nanotechnology expert who led the research.
“The reason we can fabricate nano-lasers with sizes smaller than that allowed by diffraction is because we made the lasing cavity out of metal nanoparticle dimers — structures with a 3-D ‘bowtie’ shape,” Odom said.
These metal nanostructures support localized surface plasmons — collective oscillations of electrons — that have no fundamental size limits when it comes to confining light.
The use of the bowtie geometry has two significant benefits over previous work on plasmon lasers: (1) the bowtie structure provides a well-defined, electromagnetic hot spot in a nano-sized volume because of an antenna effect, and (2) the individual structure has only minimal metal “losses” because of its discrete geometry.
“Surprisingly, we also found that when arranged in an array, the 3-D bowtie resonators could emit light at specific angles according to the lattice parameters,” Odom said.
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