Time-resolved X-ray diffraction: a wonderful tool for probing structural photo-induced phase transitions

Laser-driven solid-solid phase transition is a new kind of manipulation of matter by light which offers fascinating possibilities for controlling macroscopic switching of materials at different time scales from hours down to femtosecond. Slow dynamics phenomena are illustrated by a photo-induced spin transition. A sub-nanosecond laser-induced ferroelectric ordering and the opposite transformation have been observed in a molecular charge-transfer material with a 100 ps time resolution. New, exciting scientific challenges at 100 fs such as the excitation of coherent phonons and non-thermal melting are also presented.