# Interface law

An interface law models the polarized reflection and transmission coefficients of a surface, as a function of the incident vector. The most known one is given by Fresnel equations, corresponding to a raw interface between two refractive indices. Reflection and transmission may differ from Fresnel equations if the surface is not a simple refractive index jump, for instance when a thin film is inserted.

# Fresnel

Specular material with a glass bulk medium and a Fresnel law

### Summary

The Fresnel interface law computes reflection and transmission coefficients from Fresnel equations. For this, it uses the refractive indices of scene media located in front and behind the surface. These media are associated to materials and scene geometry (closed volumes), and not to the interface law itself.

It is especially suited for dielectric materials, such as glass, polymers, water, etc...

# Complex Fresnel

Specular material with a complex Fresnel law associated with a copper medium

### Summary

The Complex Fresnel interface law computes the reflection coefficient from Fresnel equations generalized to complex refractive indices. This is especially suited to describe metallic and semiconductor surfaces. As materials with complex refractive indices are opaque behind a few µm, the model assumes zero light transmission.

# Foil

Specular material with no bulk medium and a foil law with 0.1mm blue polymer medium

### Summary

The Foil interface law models a dielectric foil. The refractive indices of scene media located in front and behind the surface are taken into account, as well as the properties of the layer. It assumes incoherent optics within the foil.

This law is well suited for flat glass sheets, polymer foils, liquid films, etc...

# Thin film

Specular material with a glass bulk medium and a 15nm silver thin film law

### Summary

The thin film interface law models a thin film layer at the interface. The refractive indices of scene media located in front and behind the surface are taken into account, as well as the properties of the thin film. It assumes fully coherent optics within the film.

# Mixed tabulated

Specular material with a glass bulk medium and a mixed tabulated law built from dichroic thin film data

### Summary

The Mixed Tabulated interface law allows giving tabulated spectral values for reflection and transmission coefficients as a function of incidence angles. The coefficients are unpolarized (mixed polarization).

# Polarized tabulated

Specular material with a glass bulk medium and a polarized tabulated law built from dark reflective coating data

### Summary

The Mixed Tabulated interface law allows giving tabulated spectral values for reflection and transmission coefficients as a function of incidence angles. The coefficients are polarized and given separately for s and p planes.

# Classic

Specular material with a glass bulk medium and a classic law, with r0=0.04, brownish transmission color, and bluish reflection color

### Summary

The Classic interface law computes reflection and transmission coefficients from a simple model adjustable with non physical, artistic factors.

# Simple

Specular material with a glass bulk medium and a classic law, with r0=0.04

### Summary

The Simple interface law computes reflection and transmission coefficients from a simple non-physical equation approximating Fresnel coefficients, the Schlick's approximation

# Null

Specular material with a smoke medium (n=1.0) and a null law

### Summary

The Null interface law has always 100% transmission and 0% reflection. It can be used for modeling a perfect anti-reflection filter, or interfaces between various absorbing media having the same refractive index.