Electron–Phonon Coupled Heat Transfer and Thermal Response Induced by Femtosecond Laser Heating of Gold

Ab initio simulation is one of the most effective theoretical tools to study the electrons evolved heat transfer process. Here, we report the use of finite-temperature density functional theory (DFT) to investigate the electron thermal excitation, electron–phonon coupled heat transfer, and the corresponding thermal response induced by energy deposition of femtosecond laser pulse in gold. The calculated results for cases with different scales of electron excitations demonstrate significant electron temperature dependence of electron heat capacity and electron–phonon coupling factor. Bond hardening of laser-irradiated gold and structural variation from solid to liquid are observed. The obtained results shed light upon the ultrafast microscopic processes of thermal energy transport from electron subsystem to lattice subsystem and serve for an improved interpretation of femtosecond laser–metal interaction.

Experimental Investigation of Ultrafast Thermalization Dynamics on Nickel Thin Films

In order to break the limitation of the speed of magnetic installation due to magnetic layer transfer characteristics, the ultrafast thermalization dynamic of Ni films and its composite films were studied by femtosecond laser pump-probe technique. The paper focuses on the research of the effect of cooling layer and annealing on the transient reflectivity curves. And the transient reflectivity signals of Ni films prepared under different parameters were measured. The results show that the cooling layer with the larger electron heat capacity constant and the stronger electron-phonon coupling constant can enhance the scattering efficiency of transient heat conduction. Compared to the unannealed sample, the composite film sample after annealing has faster recovery process.

Influence of Inter- and Intraband Transitions to Electron Temperature Decay in Noble Metals After Short-Pulsed Laser Heating

This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on the electron temperature decay in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. The two temperature model describing electron-phonon heat transfer after short-pulsed laser heating is solved using the expressions for heat capacity and electron-phonon coupling factor after intra- and interband excitations, and the predicted electron temperature change of the intra- and interband excited electrons are examined. A critical fluence value is defined that represents the absorbed fluence needed to fill all available states at a given photon energy above the Fermi level. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ and are shown to affect temporal electron temperature profiles.