Femtosecond laser-induced structural dynamics of Nickel (111) single crystal. An ultrafast time-resolved x-ray diffraction study.

Femtosecond, 8.04 KeV x-ray pulses, generated from a table-top system, are used to probe the lattice dynamics of 100 nm and 150 nm Ni (111) single crystals grown on sapphire substrates and irradiated with 800 nm, 100 fs laser pulses. At pump fluencies below the damage and melting threshold, we observed lattice contraction due to the formation of a blast force, and coherent acoustic phonons with a period of 35 ps and 46 ps for the 100 nm and 150 nm Ni (111) films, respectively. The spatiotemporal distribution of electron, spin, and lattice temperatures within the 150 nm thick nickel single crystal was also simulated using the three-temperature model. In addition to the ultrafast heating within the skin depth, this study also revealed the tens of picoseconds time required for heating the hundred nanometer bulk of the Ni (111) single crystal.