Ultrafast Diffraction Reveals Melting

An experimental setup by researchers from the University of California, San Diego, in La Jolla, and Universität Essen and Universität Hannover, both in Germany, has allowed them to detect and monitor the nonthermal melting of germanium by laser irradiation. Ultrafast x-ray diffraction images of 160-nm-thick germanium films were produced for nine probe-pump delays with an accuracy of ±1 ps.

The team focused an 800-nm chirped-pulse-amplified Ti:sapphire laser at f/3 onto a moving copper wire. Peak intensities of 1017 to 1018 W/cm² produced the 1.54-Å x-ray radiation for the probe measurements. The laser also excited the germanium film.

The researchers published their results in the Nov. 12, 1999, issue of Science.