The precise creation of nanoscale light fields is fundamental in emerging nanophotonics and nanooptics. Approaches to directly convert light into electrical impulses, along with the non-destructive and accurate image of nanoscale light, can be very beneficial.
Study: Nanoscale light field image with graphene. Image credit: Kateryna Kon /Shutterstock.com
In a study published in the journal Communications Materials, a nanometer light field imaging technique was developed, centered around photodetection by a pn junction that is generated and displaced by the gate voltage within a probe. of graphene, generated by a series of external electrodes.
Current state of nanophotonics
Modulation and characterization of light at the nanoscale are two foundations of contemporary nanophotonics. Considerable advances have been made in this area recently through the use of plasmonic components and their combinations, plasmonic waveguides, superlenses, optical phononics, and graphene-based plasmonics.
Meanwhile, for the most part, the image and characterization of the light field still depend on microscopy approaches: measurement of scattered scattering optical fields that are limited to the diffraction threshold, restricting spatial resolution to a small part of the full light wavelength.
Near field microscopy methods for improving the light field image
The use of near optical fields can dramatically increase the accuracy of the light field image. However, the basic six-power modulation of the scattered power using probe sizes in near-field optical microscopy restricts the practical resolution for direct light tracking to 50 nanometers at visible wavelengths.
Because the mapped optical fields are dispersed by a probe submerged in an examined near-optical field, conventional near-field microscopy is therefore essentially invasive.
Scattered scanning near-field optical microscopy (s-SNOM) with interferometric pseudo-heterodyne detection, the power of contemporary near-field optical characterization, uses demodulation of received signals at high harmonics to attenuate background noise. This is a fairly effective strategy; however, it generates image distortions when examining fields with multiple spatial frequency bands.
Optical Vs. Electron microscopy
Different methods of electron microscopy, such as cathodoluminescence (CL) microscopy and electron energy loss spectroscopy (EELS), have been practiced to obtain details on the optical behavior of nanoscale structures with unmatched spatial accuracy, at the subnanometric level, through the use of electron beams.
Examination of matching EELS spatial maps or discharged radiation bands, measuring the efficiency of resonance excitations of hybrid polariton forms, and linking efficiency measurements with spatial distributions of polariton forms provides optical details. .
Thus, electron microscopy approaches provide an indirect pathway to optical details, which must be extracted using complicated data processing techniques, mainly those related to resonance excitations.
Indirect light imaging methods
Indirect light imaging technologies based on scattered fields can achieve extraordinarily fine spatial accuracy of up to one nm.
For example, Brownian motion of a pigment particle was monitored to capture the fluorescence signature of a single hot spot with a resolution of one nm. Surface-enhanced Raman spectroscopy (SERS) can be used to evaluate electric fields with a spatial resolution of five nm, while retrodysphoid radiation can be used to detect optical oscillatory trends of plasmonic modes with a resolution of ten nm. using s-SNOM.
Unfortunately, despite offering incredibly high spatial resolutions, these indirect approaches are often invasive and depend on specific assumptions that allow the observed values to be converted into light field maps.
Highlights of the study
In this study, the team proposed and tested electromagnetic field projections based on nanophotonic detection using a pn junction produced and displaced within the graphene by an externally applied gate voltage.
The width of the 20 nanometer pn junction determined the spatial accuracy of the electrical scanning approach, which can be further increased by reducing the dielectric thickness of the gate.
An external gate voltage can accurately regulate the location of this type of pn joint. The optical field mapping plane is defined by the graphene surface, which must be placed near a nanometer-sized structure that produces nanoscale light fields for characterization.
The proposed method was illustrated by tracing the electric field propagation of a highly restricted plasmon slot waveguide mode at telecommunication wavelengths, obtaining a mode profile that fit the predictions perfectly. numerical.
In particular, the unique arrangement demonstrated strong electro-optical modulation properties, with a modulation depth of 0.12 dB μm-1 at a gate voltage amplitude of 6 V.
The non-invasive light mapping technique introduces a new perspective on nanophotonic characterization, ensuring extraordinarily high spatial resolution and accuracy while presenting exciting potential for chip nanoplasmonic systems.
References
Yu, T., Rodriguez, F. et al. (2022). Nanoscale light field image with graphene. Communication materials. Available at: https://doi.org/10.1038/s43246-022-00264-0
Disclaimer: The views expressed herein are those of the author expressed in private and do not necessarily represent the views of AZoM.com Limited T / A AZoNetwork the owner and operator of this website. This disclaimer is part of the Terms and Conditions of Use of this website.