Abstract

We report the use of the transient grating method to time resolve the ultrafast thermal expansion of a surface. Measurements are performed on p-type GaAs (100) in the reflection grating geometry. By utilizing a 100-fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion from heating and subsequent contraction caused by cooling provide the dominant influence on the probe. The signal observed has a 22-ps rising edge due to thermal expansion and a 280-ps decay from heat propagation away from the heated region. The diffracted signal is composed of two components, heat conduction into the bulk perpendicular to the surface and heat flow parallel to the surface that fills in the nulls of the transient grating. By varying the fringe spacing of the grating it should be possible to separate the signal contributions to the expansion and contraction of the lattice. In this case, the dominant contribution to the rising edge appears to be the expansion perpendicular to the surface, while the conduction of heat away from the region has contributions from both components.

© 1991 Optical Society of America