Xinyu Tan

A new model for studying the plasma plume expansion property during nanosecond pulsed laser deposition

A physical model is proposed to study the laser-induced plasma dynamics expansion during irradiation of material by a high-intensity nanosecond pulsed laser beam. Based on a consideration of the plasma ionization effect and local conservations of mass, momentum and energy, combined with the assumption that plasma can be viewed as a compressible ideal fluid and a high temperature–high pressure ideal gas, we developed a new dynamics expansion mechanism for plasma produced by pulsed laser radiation. A set of new plasma expansion dynamics equations based on our model are first deduced. Then, taking the example of the carbon target, using the finite difference method, the plasma flow dynamics into a vacuum, such as plasma spacial number density distribution, plasma number density and velocity evolvement in radial and axial directions, are studied in detail. The results show that there are some main factors affecting the velocity distribution of the plasma, including the temperature of the plasma, the ionization fraction of the plasma and the dynamic source provided by the vaporized material. The velocity uz in the longitudinal direction is different from ur in the transverse direction because of huge initial eject velocity and evaporated dynamic source. The velocities of the plasma calculated by this model are found to be in better agreement with the experimental results derived from the work of Sanz et al (1985 Plasma Phys. Control. Fusion 27 329) compared with the conventional model.

EFFECTS OF PLASMA SHIELDING ON PULSED LASER ABLATION

We have developed a theoretical model which studies the characteristics of laser-plasma interaction, the effect of plasma shielding and plasma radiation in the ablation process. The model is used to simulate 25 ns square pulsed laser irradiation on YBa2Cu3O7 targets, and pulsed laser with the pulse width of 25 ns (FWHM) irradiation on Ni targets. The evolution of the plasma length and the transmitted intensity are performed. The model shows the variation of ablation depth with energy density. Moreover, we obtain the dependence of the ablation depth on the number of laser pulses. The satisfactorily good agreement between our results and experimental results confirms that plasma shielding plays a relevant role in the ablation process.