The Design Editor is the window where you build a coating. You add and order layers, choose each layer’s material and thickness, set the substrate and the surrounding media, and pick which surface you are designing. Every other window — Optical Evaluation, Admittance, Refinement, the tolerance tools — reads from this same shared design, so anything you change here is reflected everywhere at once.

A design carries two coatings: a front coating on the incident side and a back coating on the exit side. The Front and Back tabs at the top switch which one you are editing. In both tabs the layer touching the substrate is listed first, so the two coatings read consistently.

Settings

Reference wavelength λ₀ — the wavelength that drives the QW and FW thickness columns. A typical value for visible coatings is 550 nm. When you change λ₀, layers keep their quarter-wave counts: a quarter-wave layer stays a quarter-wave, and only its physical thickness rescales.

Substrate — the substrate material and its physical thickness in millimetres. When you evaluate the whole part (both sides), the substrate is treated as optically thick, so reflections inside it combine as intensities rather than amplitudes.

Incident / Exit media — the media on either side of the part, usually air on both. Pick any catalog material for immersed or cemented designs.

Surface and Ignore other side — the controls that decide which coating the optimizer moves and what every window evaluates. See Surface & Evaluation Modes for the full behavior.

Average over illumination cone — optional convergent- or divergent-beam averaging, off by default. When on, every reflectance, transmittance and absorptance result is averaged over a cone of incidence angles instead of a single collimated ray, and a live readout shows the numerical aperture, f-number and full aperture for the half-angle you enter. You choose the intensity distribution across the cone (uniform, Lambertian, or a table you enter) and the number of angular sample points. Because the averaging happens in one place, every operand and every window that evaluates the design is cone-averaged automatically while it is on. With a cone active, s and p polarization are still computed but are formal — a cone is physically rigorous only for averaged polarization, since each ray has its own plane of incidence.

The layer table

Each row is one layer: its material, four thickness columns, a lock toggle, and buttons to move, duplicate or delete it. The four thickness columns show the same physical layer in different units, and all four are editable — edit any one and the other three update from it. Physical nm is the stored value.

Column	Unit	Definition
nm	physical thickness	d
OT	optical thickness	n(λ₀) · d
QW	quarter-waves at λ₀	4 · n(λ₀) · d / λ₀
FW	full-waves at λ₀	n(λ₀) · d / λ₀

The lock toggle freezes a layer’s thickness: locked layers are excluded from optimization and synthesis, which is useful for protecting an adhesion or substrate-adjacent layer. The toolbar above the table adds and removes layers, inverts the layer order, locks or unlocks the whole side at once, and copies the current side’s stack onto the other surface. You can also insert, delete and duplicate rows from the keyboard.

Stack geometry

Below the table, a cross-section diagram shows the incident medium, the front coating, the substrate, the back coating and the exit medium, colored by material. Beneath it, a summary reports the layer count and total physical thickness for each side. The substrate, media and reference-wavelength settings collapse into this panel so the layer list keeps its vertical space.

How to read it

The cross-section is the quickest sanity check that the stack you built is the stack you meant — the right number of layers in the right order, the substrate in the middle, the media at the edges. The per-side totals tell you how much material the coating will take to deposit. The Optimize and Eval badges at the top show which side the optimizer is moving and which surface is being scored, so you always know what the numbers in the analysis windows refer to.

Coating layers are coherent — the transfer-matrix method combines their amplitudes. When you evaluate the whole part, the substrate is treated as incoherent: it is optically thick, so interference inside it averages out and the front, substrate and back contributions combine as intensities. In a single-surface evaluation the substrate is simply a semi-infinite exit medium.

References

• H. A. Macleod, Thin-Film Optical Filters, 5th ed., Ch. 2 (transfer matrix), §2.6.4 (two-sided combination).
• H. A. Macleod, Thin-Film Optical Filters, 5th ed., §3.1 (optical thickness units), §16 (cone response at oblique incidence).