A Picosecond View of Melting

Conventional diffraction techniques cannot capture the rapid changes in atomic configuration that accompany processes such as melting or chemical reactions. In his Perspective, [von der Linde][1] highlights the report by [ Siwick et al .][2], who use diffraction of ultrashort electron pulses to obtain snapshots of atomic structures with a time resolution of 500 femtoseconds. After heating aluminum metal very rapidly with a femtosecond laser pulse, they monitor the rapid changes in atomic configuration by recording time-dependent electron diffraction patterns. A picosecond after the laser excitation, a strongly superheated state of the solid phase is formed. During the next few picoseconds, long-range crystalline order is destroyed and a structure characteristic of the liquid state emerges. [1]: http://www.sciencemag.org/cgi/content/full/302/5649/1345 [2]: http://www.sciencemag.org/cgi/content/short/302/5649/1382