Bright upconverted emission from light-induced inelastic tunneling.

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.