Investigation into surface absorption of engineering materials due to laser irradiation

The electromagnetic theory of light, which is based on the solution of the Maxwell equations, generally leads to results which are in qualitative agreement with experimental results. However, there are deficiencies in this method which are due to the phenomenological nature of the analysis. In order to explain the interaction of electromagnetic waves with matter more accurately, the ideas of Lorentz are used such that dielectrics contain electrons, which are bound by quasi-elastic forces being proportional to the distance from the equilibrium position, have a natural frequency of vibration. Therefore a model of the light absorption process becomes possible. Thus, the variation of the absorption factor and reflectivity with optical frequencies are considered in four optical regions. It is found that the absorption factor is high in the near-infrared region, therefore, most of engineering materials absorb Nd YAG radiation. However, a considerable decrease in the absorption factor occurs for 10.6 μm radiation (CO₂ laser). The absorption factors drop to about 10% for an idealised surface and steps are necessary to increase the absorption factor in laser processing of engineering materials.