  Despite of the tremendous efforts spent on the oxygen vacancy migration in
determining the property optimization of oxygen-vacancy enrichment transition
metal oxides, few has focused on their dynamic behaviors non-equilibrium
states. In this work, we performed multi-timescale ultrafast X-ray diffraction
measurements by using picosecond synchrotron X-ray pulses and femtosecond
table-top X-ray pulses to monitor the structural dynamics in the oxygen-vacancy
ordered SrCoO2.5 thin films. A giant photoinduced strain ({\Delta}c/c > 1%) was
observed, whose distinct correlation with the pump photon energy indicates a
non-thermal origin of the photoinduced strain. The sub-picosecond resolution
X-ray diffraction reveals the formation and propagation of the coherent
acoustic phonons inside the film. We also simulate the effect of photoexcited
electron-hole pairs and the resulting lattice changes using the Density
Function Theory method to obtain further insight on the microscopic mechanism
of the measured photostriction effect. Comparable photostrictive responses and
the strong dependence on excitation wavelength are predicted, revealing a
bonding to anti-bonding charge transfer or high spin to intermediate spin
crossover induced lattice expansion in the oxygen-vacancy films.
