The Refractive Index Profile draws the refractive index n(z) and extinction coefficient k(z) as a step function of depth through the front coating. It is a structural view of the design rather than an optical one: it makes the actual index contrast between layers visible at a glance, which is a quick way to confirm the stack is built from the materials you intended and to see how strong the high/low index alternation is.

Each layer’s dispersive n and k are evaluated at the chosen wavelength and laid out from the incident medium through the layers to the substrate.

Settings

Wavelength — the wavelength at which each material’s index is sampled, in nm. It defaults to the design’s reference wavelength. Because the materials are dispersive, changing it shifts the index values.

Quantity — plot the refractive index n, the extinction coefficient k, or both together on twin axes.

Side — profile the front coating, the back coating, or the total structure. Front and back each lay their layers out from the incident medium through to the substrate. Total is a structural view of the whole part — the front coating, the substrate and the back coating laid end to end in one continuous profile; because the substrate is far thicker than the coatings it is drawn as a compressed middle section, with a break on either side, so the coating layers stay readable.

How to read it

The horizontal axis is physical depth in nanometres; colored bands and dotted lines mark the layer boundaries and materials. The height of each step is the index of that layer — tall contrast between neighbouring steps means a strong optical interface. A non-zero k step flags an absorbing layer.

The readout reports the index range, the layer count, and both the physical and optical total thickness, and the data table lists n and k versus depth. Reading this against the Electric Field profile shows which layer carries the standing-wave peak.

References

• H. A. Macleod, Thin-Film Optical Filters, 5th ed., §2.2 — refractive index conventions.