General Problems of Propagation of Laser Radiation in Gases and Plasma and Physical Processes on the Surface of Condensed Media

Abstract

AbstractLaser processing of materials is usually performed by focused radiation, many operations requiring very tight focusing. The focal spot size cannot be made as small as one likes due to diffraction of a light beam. The laser beam focusing can be also restricted by nonlinear processes. Because laser radiation used for material processing has high average or peak powers, this radiation can change the optical properties of media in which it propagates. The so-called self-action effects such as radiation self-focusing or self-defocusing appear. In addition, light can be noticeably absorbed in a medium. Technical industrial conditions may require sometimes the transport of light over long distances in air or through condensed media (in the case of special technologies), and these effects can become significant. Plasma often produced during various technological processes can strongly affect the propagation of light, in particular, IR radiation at λ = 10 μm. In this chapter, we consider this question only briefly. The propagation of radiation in the optical discharge plasma will be discussed in detail in Chap. 3. The efficiency of action of light incident on a sample depends on the absorption coefficient of the latter. For example, during laser welding and drilling light propagates in a narrow channel, where it is multiply reflected from walls. The properties of such propagation of light will be also considered in this chapter. Laser radiation can heat, melt, evaporate, and ionize the sample material. During heating in an oxidizing medium, the sample material can be oxidized. During melting of the sample, the motion of the melt can appear due to Marangoni effect and capillary instabilities can develop. If the radiation intensity is sufficient to initiate the evaporation of the target, specific evaporative instabilities can appear. We will briefly discuss all these phenomena in this chapter.KeywordsLaser RadiationMach NumberRadiation IntensityVelocity Distribution FunctionKnudsen LayerThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.