Determination of the complex refractive index of a thick slab material from its spectral reflectance and transmittance at normal incidence

Multiple beam incoherent reflectance, transmittance and absorbance of a homogenous planar slab are derived by ray tracing and transfer matrix approaches. Two different procedures are introduced to retrieve the bulk complex refractive index analytically. The needed experimental measurements are the slab thickness, the spectral reflectance and transmittance at normal incidence. Errors of the deduced refractive indices are calculated to be of about 1 × 10−7 for imaginary and 0.013 for real refractive indices. Refractive indices of two different thicknesses and compositions glassy slabs are determined across a wide spectral range 0.22–2.2 μm.