CHARACTERISTICS OF RADIATION ABSORPTION IN METALLIC PARTICLES

Thermal radiation absorption in metallic particles is an important phe nomenon in many contemporary laser-processing techniques, including la ser cladding of coating materials and laser cleaning of particulate co ntaminations. In this work, the Drude free-electron theory and electro magnetic wave theory are utilized to characterize the internal absorpt ion of CO2 laser radiation in aluminum, chromium, and nickel particles . The results show that metallic particles have unique radiation prope rties. Radiation absorption in large particles occurs only in a very n arrow region of the front particle surface, which results in inefficie nt radiation absorption. On the other hand, micron and submicron parti cles can absorb radiation very efficiently, due to the strong diffract ion effect at the particle surface. For extremely small particles (e.g ., nanometer particles), radiation absorption becomes less efficient. The particle absorption efficiency is found to increase with temperatu re, and this temperature dependence can be determined from those of fl at metal surfaces at the normal incidence.