We demonstrate that the absorption of femtosecond hard x-ray pulses excites quasispherical. high-amplitude. and high-wave-vector coherent acoustic phonon wave packets using an all hard-x-ray pump-probe scattering experiment. The time- and momentum-resolved diffuse scattering signal is consistent with an ensemble of 3D strain wave packets induced by the rapid electron cascade dynamics ... https://www.markbroyard.com/