Observations of ablation plumes produced by two delayed short laser pulses: a new method for probing electron-phonon coupling in metals

International audienceThe 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

Characterization of ablation plumes produced by the interaction of short laser pulses with materials

International audienc

Probing electron-phonon coupling in metals via observations of ablation plumes produced by two delayed short laser pulses

International audienceWe investigate electron-phonon coupling in metals by analyzing the composition of plumes produced by laser ablation with two delayed short laser pulses. Samples of Ti, Zr, and Hf are chosen since they have similar thermo-physical properties but significant different atomic masses. It is shown that the atomic emission intensity increases with the interpulse delay, whereas the nanoparticle emission intensity decreases. The characteristic time of plume changes is found to depend linearly on the metals' atomic mass. Theoretical considerations suggest that the measured times equal to the characteristic times of electron-lattice relaxation

Properties of plasmas produced by short double pulse laser ablation of metals

26th Summer School and International Symposium on the Physics of Ionized Gases (SPIG), Zrenjanin, SERBIA, AUG 27-31, 2012International audienceWe investigate the composition of plasmas produced by laser ablation of metals with two time-delayed short laser pulses using fast imaging and time- and space-resolved optical emission spectroscopy. The ablated material is deposited on mica substrates and analyzed by atomic force microscopy. The laser-produced craters are inspected by optical microscopy to evaluate the ablated material quantity. It is shown that the fraction of nanoparticles in the ablation plume is strongly altered when a second laser pulse of sufficiently large delay is applied. Comparing the results obtained for different metals, we observe a significant nanoparticle reduction for interpulse delays of the order of the characteristic time of electron-lattice thermalization. More detailed analyses show that the plume changes occur on two different characteristic times, indicating two different mechanisms at its origin. Here, we discuss the involved processes and we propose a simple and efficient technique for the measurement of electron-lattice thermalization times based on plume observations during double pulse laser ablation

Evaluation of pressure in a plasma produced by laser ablation of steel

We investigated the time evolution of pressure in the plume generated by laser ablation with ultraviolet nanosecond laser pulses in a near-atmospheric argon atmosphere. These conditions were previously identified to produce a plasma of properties that facilitate accurate spectroscopic diagnostics. Using steel as sample material, the present investigations benefit from the large number of reliable spectroscopic data available for iron. Recording time-resolved emission spectra with an echelle spectrometer, we were able to perform accurate measurements of electron density and temperature over a time interval from 200 ns to 12 μs. Assuming local thermodynamic equilibrium, we computed the plasma composition within the ablated vapor material and the corresponding kinetic pressure. The time evolution of plume pressure is shown to reach a minimum value below the pressure of the background gas. This indicates that the process of vapor-gas interdiffusion has a negligible influence on the plume expansion dynamics in the considered timescale. Moreover, the results promote the plasma pressure as a control parameter in calibration-free laser-induced breakdown spectroscopy