Materials with Thickness Dependent Optical Properties

(NEW! Starting from Version 13.77)

ThickVar materials have optical properties depending on layer thickness. A typical example of this type of materials is metal-island films (Fig. 1).

Usually with the help of characterization the optical properties of such material are determined for several typical thicknesses (Fig. 2).

We assume that they are saved to the Layer Material database with the names reflecting these thicknesses for convenience (Fig. 3).


Fig. 1. Typical structure of a metal-dielectric film: Ag island film is surrounded by two SiO2 layers (sandwich).

metal-island films

Fig. 2a. Refractive indices of Ag-SiO2 metal-island films for different thicknesses of Ag.

metal-island films extinction

Fig. 2b. Extinction coefficients of Ag-SiO2 metal-island films for different thicknesses of Ag. 

thickness dependent optical constants

Fig. 3. Specification of thickness dependent optical constants in the new ThickVar tab. You specify a dispersion file (left column) and the corresponding Ag-thickness.

metal-dielectric films

Fig. 4. In Preview tab, you can see optical constants for any thickness specified in Layer Thickness field.

Example: To design a coating, which reflects orange and violet colors from its front and back sides. Also, solar transmittance should be more than 50%. Light source D65.

Layer materials: SiO2, TiO2.

In order to achieve different colors from the front and back sides of the substrate, an absorbing layer is required. Metal-island film is a good solution. It is not clear, however, what thickness of Ag should be. OptiLayer finds this thickness automatically in the course of the design process. 

ThickVar Material Ag-SiO2 (Fig. 3) must be loaded.

  • The color coordinates can be specified in color target, for example, in La*b* system:
  • a*=25, b*=60 (for reflectance R);
  • a*=-60, b*=50 (for back side reflectance BR);
  • L*=50% (for R/BR)
  • Solar transmittance > 50% (can be specified using integral target).
  • Thicknesses of the surrounding SiO2 layers should be greater than 40 nm.
  • The design can contain only one metal-dielectric layer of Ag-SiO2.


Good designs can be found starting from the sandwich structures SiO2 (78 nm) - Ag-SiO2 (ThickVar Material) any reasonable thickness - SiO2 (78 nm) with the help of gradual evolution with subsequent constrained optimization. Thickness of the  Ag-SiO2 films are about 15-17 nm.

color space Lab

Fig. 5. Color coordinates of reflectance and back side reflectance of the design with the profile shown in Fig. 8.

solar transmittance calculation

Fig.6. Solar transmittance of the design shown in Fig. 8 is greater than 50%.

refractive index depends on thickness

Fig. 7. Reflectance and back side reflectance of the solution shown in Fig. 8.

metal-dielectric coating

Fig. 8. A 8-layer metal-dielectric solution satisfying all conditions presented above: the design contains only one Ag-SiO2 layer, this layer is surrounded by SiO2 layers with thicknesses definitely larger than 40 nm.

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