Models of Electromagnetic Response of Materials

Physical models that relate the generalized complex permittivity and complex conductivity to the electronic structure of matter are introduced. The classical models of Drude and Lorentz give expressions for the complex index of refraction in a dielectric, while Drude models a metal as a plasma. Reflection and transmission properties of interfaces are expressed in terms of the complex index of refraction. Special consideration is given to the behavior of light propagation in the frequency vicinity of an atomic resonance of the material. Finally, measurement techniques are presented that are applicable to the determination of the parameters of a Lorentz/Drude representation of electromagnetic transmission in matter.

Numerical Simulation of the Relation between Plasma Reflection and Keyhole Dimension in the Keyhole PAW Process

A three-dimensional mathematical model has been established to research the relation between the plasma reflection and status of keyhole during the keyhole PAW processing. It has been found that the strength of the plasma reflection is related to the keyhole dimension. Another condition to make the plasma refection appearance is that the keyhole or concave in the pool must be unsymmetrical about the axis of the plasma arc. The mechanism of detecting circuit designed based on the fact that the plasma refection is able to indicate the status of keyhole is mathematically studied. The result shows that the voltage signal in the detecting circuit can be used to indicate the status of keyhole.