Three-dimensional acoustic wavefront imaging in anisotropic systems by picosecond acoustics

We present a laser ultrasonics experiment with imaging capabilities performed in transmission through semiconductor substrates. Such experiment provides a new kind of bulk wavefront imaging using an ultrafast optical generation and detection scheme for gigahertz waves. The data may be viewed as two-dimensional slices of the three-dimensional acoustic wavefront revealing the basic anisotropy of the solid with 0.3 ps time resolution and 3 μm space resolution and allowing the determination of the whole set of elastic constants for various experimental conditions. As examples, measurements are carried out in a Si(001), GaAs(001), and GaAs(111) sample at 20 and 300 K.