Parameters of a Simple Scattering Surface

The surface quality does not depend on incidence angle, polarization etc. It works according to reflection only, transmission only, or reflection and transmission.

Note: A global absorption is when there is no dependency with the wavelength.

A Lambertian reflection is when there is dependency with the wavelength. The Lambertian reflection is not available in the Simple Scattering Surface Editor. If you need to define a spectrum, use the Advanced Scattering Surface Editor.

  • In all cases, when a photon hits a surface with this surface state, the surface absorption and the percentages of reflection and transmission are first computed according to the photon incidence and wavelength.

  • In the case of propagation with photon weight, the absorption is subtracted to the photon energy. The photon is propagated after the interaction with the surface with the new energy.

  • In the case of propagation without photon weight, the absorption is the probability for the photon to be absorbed.

A random number is then computed to choose the interaction type (reflection or transmission, specular, Gaussian or Lambertian, and absorption in the case of propagation without photon weight) and their respective probabilities.

Warning: Calculations take into account incidence following the Snell law.

Absorption

Absorption: the value of the absorbed energy in percent.

Non Absorption

The Non absorption gives the non absorbed energy.

Non absorption = P = (100 - Absorption).

P is computed and used as following:

  • Reflection or transmission only: The percentages of Lambertian, Gaussian or specular reflection (or transmission) are percentages of P. All other percentages of transmission (or reflection) are set to 0.

  • Reflection and transmission:

    • If Use Fresnel is selected, the Fresnel law gives the percentages of reflection (Rf) and transmission (Tf) according to the photon incidence and wavelength.

    • If User is selected, type the percentage of reflection (Rf) and the transmission (Tf) is computed as 100-Rf. The global percentages are respectively:

      Rt = P * Rf / 100

      Tt = P * Tf / 100

  • Then Lambertian, Gaussian or specular percentages are percentages of Rt and Tt.

Note: In simple scattering, setting Reflection and Transmission does not avoid Total Internal Reflection.

Reflection

  • Reflection gaussian angle (in degree): the FWHM of the Gaussian part of the reflected beam.

  • Lambertian: the percentage of Lambertian scattering in reflected light.

  • Gaussian: the percentage of Gaussian scattering in reflected light.

  • Specular: the percentage of specular reflection in reflected light.

Transmission

  • Lambertian: the percentage of Lambertian scattering in transmitted light.

  • Gaussian: the percentage of Gaussian scattering in transmitted light.

  • Specular: the percentage of specular reflection in transmitted light.

  • Transmission gaussian angle (in degree): the FWHM of the Gaussian part of the transmitted beam.

Fresnel Coefficients / User values

To use Fresnel Coefficients and User values, check both Reflection and Transmission.

  • With the Fresnel Coefficients, the ratio between reflected energy and transmitted energy follows the optical Fresnel laws.

    You can use the Fresnel Coefficients only with specular surfaces: you need to set the Lambertian and Gaussian percentage to 0% for the Reflection and Transmission, so that the Specular percentage is 100%.

  • With User values, type the reflection percentage.