Studies of electron diffusion in photo-excited Ni using time-resolved X-ray diffraction
Persson A.I.H., Jarnac A., Wang X., Enquist H., Jurgilaitis A. and J. Larsson
Open Published Online: November 2016 Accepted: October 2016 – DOI: http://dx.doi.org/10.1063/1.4967470

ABSTRACT:
We show that the heat deposition profile in a laser-excited metal can be determined by time-resolved X-ray diffraction.

In this study, we investigated the electron diffusion in a 150 nm thick nickel film deposited on an indium antimonide substrate. A strain wave that mimics the heat deposition profile is generated in the metal and propagates into the InSb, where it influences the temporal profile of X-rays diffracted from InSb.

We found that the strain pulse significantly deviated from a simple exponential profile, and that the two-temperature model was needed to reproduce the measured heat deposition profile.

Experimental results were compared to simulations based on the two-temperature model carried out using commercial finite-element software packages and on-line dynamical diffraction tools. To reproduce the experimental data, the electron–phonon coupling factor was lowered compared to previously measured values.

The experiment was carried out at a third-generation synchrotron radiation source using a high-brightness beam and an ultrafast X-ray streak camera with a temporal resolution of 3 ps.