Third Harmonic Generation in Graphene (IMAGE) Graphene Flagship Caption Electrical control of third harmonic generation (THG) can be obtained in single-layer graphene. In THG three low-frequency photons (red) sum up to generate one high-frequency (blue) photon. For this reason, THG can be used for optical frequency converters. Credit Giancarlo Soavi, University of Cambridge Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.