Sheet-like materials can have intriguing properties that could benefit devices from flexible electronics to solar cells. Researchers think they can customize the properties of these materials by using light pulses to rapidly switch the materials from one state to another. For example, light pulses could turn an electrical insulator into a conductor. But the ability to do this depends on how efficiently the light’s energy is transferred to the material’s atomic nuclei. Now, researchers have shown, for the first time, that the conversion of light to atomic vibrations in thin sheets of molybdenum diselenide is very fast and efficient. In fact, the conversion is nearly 100 percent efficient and occurs in a trillionth of a second.