The laser, as a source of “pure” energy in the form of monochromatic and coherent photons, is enjoying ever increasing popularity in diverse and broad applications from drilling micron-sized holes on semiconductor devices to guidance systems used in drilling a mammoth tunnel under the English Channel. In many areas such as metallurgy, medical technology, and the electronics industry, it has become an irreplaceable tool.Like many other discoveries, the various applications of the laser were not initially defined but were consequences of natural evolution led by theoretical studies. Shortly after the demonstration of the first laser, the most intensely studied theoretical topics dealt with laser beam-solid interactions. Experiments were undertaken to verify different theoretical models for this process. Later, these experiments became the pillars of many applications. Figure 1 illustrates the history of laser development from its initial discovery to practical applications. In this tree of evolution, Pulsed Laser Deposition (PLD) is only a small branch. It remained relatively obscure for a long time. Only in the last few years has his branch started to blossom and bear fruits in thin film deposition.Conceptually and experimentally, PLD is extremely simple, probably the simplest among all thin film growth techniques. Figure 2 shows a schematic diagram of this technique. It uses pulsed laser radiation to vaporize materials and to deposit thin films in a vacuum chamber. However, the beam-solid interaction that leads to evaporation/ablation is a very complex physical phenomenon. The theoretical description of the mechanism is multidisciplinary and combines equilibrium and nonequilibrium processes. The impact of a laser beam on the surface of a solid material, electromagnetic energy is converted first into electronic excitation and then into thermal, chemical, and even mechanical energy to cause evaporation, ablation, excitation, and plasma formation.
Interaction of Laser beam, Powder Stream and Molten Pool in Laser Deposition Processing with Coaxial Nozzle
