Observations of ablation plumes produced by two delayed short laser pulses: a new method for probing electron-phonon coupling in metals
Résumé
The electron-phonon coupling in metals was investigated during laser ablation with two delayed short laser pulses by analyzing the influence of the interpulse delay onto plumes composition. Metal targets of Ti, Zr, and Hf were chosen since they have similar thermophysical properties but significant different atomic masses. The expansion dynamics of atoms and nanoparticles was monitored by fast plume imaging as a function of laser fluence. We observed that the atomic emission intensity increases with the interpulse delay, whereas the nanoparticle emission intensity decreases. Moreover, the characteristic time of plume changes is found to depend linearly on the metals' atomic mass. Theoretical considerations indicate that the measured times equal to the characteristic times of electron-lattice relaxation. With respect to conventional pump-probe reflectivity measurements, the presented results clearly demonstrate that multipulse laser irradiation can be applied for measurements of the electron-phonon coupling.