Abstract
Upconverted light from nanostructured metal surfaces can be produced by harmonic generation and multi-photon luminescence; however, these are very weak processes and require extremely high field intensities to produce a measurable signal. Here we report on bright emission, 5 orders of magnitude greater than harmonic generation, that can be seen from metal tunnel junctions that we believe is due to light-induced inelastic tunneling emission. Like inelastic tunneling light emission, which was recently reported to have 2% conversion efficiency per tunneling event, the emission wavelength recorded varies with the local electric field applied; however, here the field is from a 1560 nm femtosecond pulsed laser source. Finite-difference time-domain simulations of the experimental conditions show the local field is sufficient to generate tunneling-based inelastic light emission in the visible regime. This phenomenon is promising for producing ultrafast upconverted light emission with higher efficiency than conventional nonlinear processes.
Highlights
Light matter interactions have been studied for decades and even before scientists, artists in Roman empire used gold nanoparticles to colour glass
Other works have shown that the deformation of the shape of the metal nanoparticle can result in a blue shift, but this effect is permanent [5], which distinguishes it from the results presented here
Other works have shown flickering of multiphoton fluorescence, but light-induced inelastic tunneling emission (LITE) differs from that flickering because it does not turn back on once it dies out [19]
Summary
Light matter interactions have been studied for decades and even before scientists, artists in Roman empire used gold nanoparticles to colour glass. The field of plasmonics that studies confinement of light to wavelength and sub-wavelength dimensions is rapidly evolving. At first, it might seem surprising because in essence it is just Maxwell’s equations, some boundary conditions and material properties. New metamaterials are invented that have optical characteristics not found in nature such as negative refractive index. New techniques are developed to create nanostructures with high precision that allow to have extremely high local fields, which improves the efficiency of nonlinear processes. Nonlinear optics is of great interest due to its many potential applications in solar cells, optical switching, sensing and many more. Semiconductor materials are used for switching and their speed is limited by charge carriers
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