Figure 1 (IMAGE) Tohoku University Caption A schematic diagram of the present echo-generation process. (a) An electron-hole pair is created by a photo-excitation pulse. (b) After the excitation, the electron and hole move in opposite directions. (c) A driving electric-field pulse reverses the relative velocity of the electron-hole pairs, resulting in the recombination of the pairs and the emission of echo pulses. Credit Atsushi Ono Usage Restrictions Reporters may use freely these materials in news coverage with appropriate credit information. License Original 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.