Light Emission from Inelastic Electron Tunneling

We report the discovery of a new method for the generation of light. This technique yields a broad-band light source with a high frequency linear cutoff which is dependent only upon the applied voltage through the quantum relation $h{\ensuremath{\nu}}_{\mathrm{co}}=|\mathrm{eV}|$. The light source consists of a metal-insulator-metal tunneling junction. The effect can be interpreted in terms of inelastic tunneling excitation of optically coupled surface plasmon modes.