New treatment of light propagation in absorbing media

Light propagation in absorbing media is of special importance in thick resist lithography. We have investigated the light propagation in absorbing media using the plane wave expansion. We observe that, for an off-axis plane wave behind an absorbing interface there is an inverse relationship between the z-component of wave-vector and the attenuation coefficient in z-direction. Unlike the classical treatment of absorption where both, the refractive index and the wave vector are extended into the complex, our treatment allows to use only real propagation quantities and thus enables a more efficient implementation. Furthermore, using a realistic approximation, the plane wave expansion in absorbing media is simplified significantly.