Electrodynamical Properties of High Tc Superconductors Studied with   Polarized Angle Resolved Infrared Spectroscopy
  Using infrared spectroscopy at grazing angle of incidence we study the electrodynamical properties of high temperature superconductors. We review some of our experiments where transverse polarized light is absorbed by longitudinal optical modes with their mode of oscillation perpendicular to the plane. This is particularly useful for the study of the plasmons and phonons perpendicular to the plane, and allows us to study in detail the c-axis dynamical properties of flux grown single crystals for which usually no samples with large dimensions in the c-direction exist. 
D. van der Marel, J. Sch\"utzmann, H. S. Somal, and J. W. van der Eb