Researchers used a sensitive scattering-type scanning near-field optical microscope (s-SNOM) to directly measure the optical fields of AGP waves propagating in a nanometer-thin waveguide to demonstrate direct near-field optical imaging of acoustic graphene plasmon (AGP) fields. Scientists could observe the thousandfold compression of mid-infrared light using this method.
The strategy paves the way for potentially groundbreaking advances in the practical application of acoustic graphene plasmon platforms for next-generation, high-performance graphene-based optoelectronic devices with enhanced light-matter interactions and lower propagation loss.
The collective oscillations of free electrons in graphene coupled to electromagnetic light waves are known as graphene plasmons. The oscillations can trap and compress optical waves inside a very thin dielectric layer that separates graphene from a metallic sheet, in a system in which graphene’s conduction electrons are “reflected” in the metal so that when lightwaves “push” the electrons in graphene, their image charges in metal oscillate as well. AGP is the name given to this phenomenon.
Previously, AGP could only be observed indirectly using far-field infrared spectroscopy and photocurrent mapping; the intensity of electromagnetic fields outside the device was considered insufficient for direct near-field optical imaging.
The new method takes advantage of graphene’s decaying but always presents an electric field. It proved that AGPs could be detected even when most of their energy is contained within the dielectric layer beneath graphene.
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