Full reconstruction of a crystal unit cell structure during coherent femtosecond motion.

We present a complete characterization of the unit cell dynamics of a laser-excited tellurium crystal using femtosecond x-ray diffraction. The analysis offers a quantitative measure of the unit cell dynamics without making any assumptions on the symmetry of the excited-state motion. The results show a large-amplitude coherently excited A(1) mode quantitatively consistent with the predictions of a density functional theory model.