Time-resolved evolution of laser-induced periodic surface structure on germanium

We have time resolved the reflection and diffraction of a probe beam from germanium during creation of periodic surface structure by a 20-ns, 1.06-{μ}m laser pulse. Large, transient diffracted signals typically precede the development of permanent structure while the maximum reflectivity is much less than the melt value. We conclude that inhomogeneous melting and resolidification of the surface occurs following the interference of the incident beam and a nonradiative electromagnetic field.