Effect of Pulse Laser Duration and Shape on PLD Thin Films Morphology and Structure

Lasers are unique energy sources characterized by spectral purity, spatial and temporal coherence, which ensure the highest incident intensity on the surface of any kind of sample. Each of these characteristics stays at the origin of different applications. The study of highintensity laser sources interaction with solid materials was started at the beginning of laser era, i.e. more than 50 years ago. This interaction was called during time as: vaporization, pulverization, desorption, etching or laser ablation (Cheung 1994). Ablation was used for the first time in connection with lasers for induction of material expulsion by infrared (IR) lasers. The primary interaction between IR photons and material takes place by transitions between vibration levels. The plasma generated and supported under the action of high-intensity laser radiation was for long considered as a loss channel only and therefore, a strong hampering in the development of efficient laser processing of materials. In time, it was shown that the plasma controls not only the complex interaction phenomena between the laser radiation and various media, but can be used for improving laser radiation coupling and ultimately the efficient processing of materials (Mihailescu and Hermann, 2010). The plasma generated under the action of fs laser pulses was investigated by optical emission spectroscopy (OES) and time-of-flight mass spectrometry (TOF-MS) (Ristoscu et al., 2003; Qian et al., 1999; Pronko et al., 2003; Claeyssens et al., 2002; Grojo et al., 2005; Amoruso et al., 2005a). Lasers with ultrashort pulses have found in last years applications in precise machining, laser induced spectroscopy or biological characterization (Dausinger et al., 2004), but also for synthesis and/or transfer of a large class of materials: diamond-like carbon (DLC) (Qian et al., 1999; Banks et al., 1999; Garrelie et al., 2003), oxides (Okoshi et al., 2000; Perriere et al., 2002; Millon et al., 2002), nitrides (Zhang et al., 2000; Luculescu et al., 2002; Geretovszky et al., 2003; Ristoscu et al., 2004), carbides (Ghica et al., 2006), metals (Klini et al., 2008) or quasicrystals (Teghil et al., 2003). Femtosecond laser pulses stimulate the apparition of nonequilibrium states in the irradiated material, which lead to very fast changes and development of metastable phases. This way, the material to be ablated reaches the critical point which control the generation of nanoparticles (Eliezer et al., 2004; Amoruso et al., 2005b; Barcikowski et al., 2007; Amoruso et al., 2007).