Creating photonic crystals could lead the way to the closing of this gap.” The breakthrough: from spatial to temporal controlThose photonic crystals are nanostructured materials with a periodic optical pattern (like a lattice) that controls the flow of photons. In previous studies, this research team had demonstrated how manipulating temperature or magnetic fields could alter the light-capturing properties of photonic crystals, but until now their control was static in time. This new work introduces the very first photonic time crystals, where the material’s optical properties (e.g., reflectivity, resonance frequency) are dynamically modulated on picosecond timescales, comparable to the light’s own oscillation cycle. “By extending photonic crystals from space to time, we open a new dimension for light control – and a novel path toward amplification and lasing.