A INTRODUCTION

The complex refractive index (usually denoted as = n + i ?) determines how light waves propagate inside a material [1]. The square of the refractive index is the dielectric function ?( ?) = ( ?) ² which contributes to Maxwell's equations the response of matter to externally applied, time varying electric fields. Plane wave solutions are obtained for electromagnetic radiation inside the material, e.g. for the electric field amplitude one finds

(1)

where ? ₀ is the light wavelength in vacuum. This means that the light wave inside the material has a wavelength differing by a factor n ^-1 from the corresponding vacuum wavelength. Since the frequency of a wave does not change when it crosses an interface between two media the phase velocity is different by the same factor also. In addition, the wave inside the material decays exponentially if the imaginary part of the refractive index does not vanish.

Not only does the propagation of light depend on the refractive index but also the reflected and transmitted fractions of waves incident on an interface between two materials. The so-called Fresnel coefficients for reflection and transmission are given by the refractive indices of the two adjacent materials.

It is clear that for any application of a material in optics or opto-electronics it is essential to know its refractive index. In the following we show how...