Revisiting optical absorption power density of inhomogeneous plane waves

Abstract

We review the analytical expressions for the complex Poynting’s vector in the case of arbitrary plane-waves in a lossy isotropic medium. We demonstrate how these expressions can be used to recover the optical absorption power density Q, considering the divergence of the time-averaged Poynting vector. This quantity, proportional to the imaginary part of the dielectric function and the field intensity, i.e. Q∝|E|2ɛ”, is usually established for harmonic fields, using the Poynting’s identity. The derivation from the complex Poynting vector expression is more direct for TE-polarized homogeneous waves, but the derivation encompasses the other cases like inhomogeneous TM plane waves. As an application, the optical absorption profile Q(x) within 1D multilayers is detailed using matrix transfer method for both TE and TM plane waves, including the evanescent case.

Keywords

• Absorption power density
• Poynting vector
• Transfer matrix method