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The pulsed-laser deposition (PLD) technique is currently used in research laboratories to obtain thin films from a broad range of materials even with a complex composition. The differences in the crystalline properties of ZnO films grown by laser ablation, using either nanosecond or femtosecond pulsed-laser deposition (PLD) is presented.

The effect of self-absorption on the time- and space-resolved emission spectra of the early phase of an ultraviolet excimer laser induced plasma was investigated. Material evaporation was achieved with the aid of an excimer laser while the laser pulse energy was measured using a pyroelectric detector. Results showed that the self-absorption of spectral lines influenced the early dense plasma stages. On the other hand, the ambient gas had no effect on the early plasma phase.

The new laser-induced plasma method of metal nitriding was evaluated via an application, namely, polycrystalline titanium nitride synthesis. The plasma-surface was characterized as a function of increasing laser shot number. To investigate the role of the laser wavelength and pulse time duration in layer formation, a transversal-excited-atmospheric-pressure carbon dioxide laser operating in the infrared regime and an XeCl excimer laser operating in the ultraviolet band were used.

Time- and space-resolved optical emission spectroscopy are used in the study of carbon dioxide laser-plasma-metal surface interaction. The plasma plume is induced by pulsed carbon dioxide laser irradiation of a titanium target at power densities of more than 400 million watts per square centimeter. The variation of laser intensity, laser temporal pulse shape, ambient gas pressure and the nature of ambient gas are utilized in the time- and space-resolved measurements. Maximum values of electron temperature and electron density are revealed by the spectroscopic diagnostics of the helium breakdown. The electron temperature is measured by the usage of the excited metal atoms that are in equilibrium with electrons.

The initiation of plasma in front of a metal sample by means of pulsed laser irradiation is studied. Experiments are conducted whereinlaser beam-metal target interactions are performed in a stainless-steel chamber. The beam is produced by a transversely excited atmospheric CO2 laser source operating at a frequency of 10 Hertz. Several ambient gases, namely: He,Ar and N2, are used in the investigation. Results reveal that laser irradiationcauses maximum vaporiization when performed in He than in Ar and N2.

Laser-induced fluorescence wasa used to investigate surface vaporization during pulsed laser irradiation of a titanium sample in the presence of an ambient gas. The results showed that strong evaporation of up toseveral hundred torr was caused in helium by laser irradiation. The Ti atom plume expanded according to the propagation of the blast wave. However, only a small amount of material was vaporized in the presence of Ar and N2.

The irradiation of a steel surface in atmospheric pressure ambient was performed to study the surface nanostructuring resulting from the formation of a backward-deposited layer. The dynamics of the plume expansion and of the nanoparticle deposition process were investigated by in situ time-resolved optical analysis. Scanning electron microscopy and atomic force microscopy were employed to investigate the morphological characteristics of the backward deposited layer. The observations revealed a particular shape of plasma expansion. The latter is characterized by the formation of two vortices at the plasma plume periphery, where a high density of condensed nanoparticles are generated. It is shown that the surface nanostructuring is mainly due to a backward nanoparticles flux which leads to a deposition process during several tens of microseconds. The effects of laser wavelength on nanoparticle formation and surface nanostructuring are presented and discussed. [ABSTRACT FROM AUTHOR]

We have studied the structural properties of ZnO thin films grown on A1[sub 2]O[sub 3] (00.1) single-crystal substrates by pulsed-laser deposition using either a femtosecond or a nanosecond laser. Although hexagonal ZnO films deposited on sapphire substrate were epitaxially grown in both cases, the crystalline quality was found to be very different: ZnO films grown with the femtosecond laser are characterized by a higher mosaicity, a smaller crystallite size, a larger content of defects but also smaller residual stresses than ZnO films obtained by nanosecond laser ablation. These differences can be explained according to the kinetic energy of the species evolved during laser ablation as deduced from plasma characterization with a charged-coupled device camera: close to 1 KeV in the femtosecond regime for the population species emitted from the target with the highest velocity, versus a few hundreds of eV in the case of nanosecond pulses. The high energy species irradiation associated with a femtosecond laser is likely to induce a large structural disorder together with stress relaxation during ZnO films growth. Physics. [ABSTRACT FROM AUTHOR]

Deals with a study which explained the influence of ambient gas on the laser beam-metal surface energy transfer. Background to the study; Experimental setup; Details of the vaporization-initiated plasma breakdown mechanism.

Focuses on a study which investigated vaporization and plasma formation resulting from excimer laser irradiation of titanium targets in a low-pressure nitrogen atmosphere. Experimental setup; Results and discussion; Conclusion.