4. Digital coding

Programming the calculation of the spectral response of a multilayer is a relatively straightforward exercise. However, in order to guarantee the general nature of the calculation (plane waves, evanescent waves, transparent or dissipative media, total reflection and resonance, extension to planar optics, microcavities, etc.), care must be taken to ensure that the core of the calculation involves only spatial frequencies, without calling on the notion of geometric angle. The flow chart based on admittances is as follows:

• the illumination conditions in the superstrate define the incident spatial pulsation: σ = 2πn ₀ sin i ₀ /λ, which is the tangential component of the wave vector. This real pulsation is none other than Descartes' invariant, since σ does...