  We present a time-resolved infrared (IR) pump and extreme-ultraviolet (XUV)
probe diffraction experiment to investigate ultrafast structural dynamics in
colloidal crystals with picosecond resolution. The experiment was performed at
the FLASH facility at DESY with a fundamental wavelength of 8 nm. In our
experiment, the temporal changes of Bragg peaks were analyzed and their
frequency components were calculated using Fourier analysis. Periodic
modulations in the colloidal crystal were localized at a frequency of about 4-5
GHz. Based on the Lamb theory, theoretical calculations of vibrations of the
isotropic elastic polystyrene spheres of 400 nm in size reveal a 5.07 GHz
eigenfrequency of the ground (breathing) mode.
