Sound velocity and index of refraction of AlAs measured by picosecond ultrasonics

We use picosecond optics techniques to generate and detect acoustic pulses in an epitaxially grown film of AlAs. From the round trip time of the acoustic pulse we find a sound velocity in the [100] direction of 6.4×10 5 cm s-1. We also show how measurements of this type can be used to determine the refractive index.