Our simulations and experiments demonstrate a new physical mechanism for detecting acoustic waves of THz
frequencies. We find that strain waves of THz frequencies can coherently generate radiation when they propagate
past an interface between materials with different piezoelectric coefficients. By considering AlN/GaN
heterostructures, we show that the radiation is of detectable amplitude and contains sufficient information to
determine the time-dependence of the strain wave with potentially sub-picosecond, nearly atomic time and space
resolution. This mechanism is distinct from optical approaches to strain wave measurement. We demonstrate
this phenomenon within the context of high amplitude THz frequency strain waves that spontaneously form at
the front of shock waves in GaN crystals. We also show how the mechanism can be utilized to determine the
layer thicknesses in thin film GaN/AlN heterostructures.
We describe experiments demonstrating the generation of ultrafast, high strain rate acoustic waves in a precompressed
transparent medium at static pressure up to 24 GPa. We also observe shock waves in precompressed aluminum with
transient pressures above 40 GPa under precompression. Using ultrafast interferometry, we determine parameters such
as the shock pressure and acoustic wave velocity using multiple and single shot methods. These methods form the basis
for material experiments under extreme conditions which are challenging to access using other techniques.