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 $h{\nu }_{\mathrm{co}}=\left|\mathrm{eV}\right|\mathrm{}$. 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.

• Received 4 June 1976

DOI:https://doi.org/10.1103/PhysRevLett.37.923