A coated part can have a coating on each side, and “the performance” can mean the front coating alone, the back coating alone, or the whole part together. TFStudio settles both questions — which coating you are designing and what the numbers mean — with just two controls in the Design Editor. They are the single source of truth: every other window (Optical Evaluation, the Specification, all the tolerance tools, and the optimizers) follows them and shows a read-only badge of the result, so two windows can never score the same design differently.
The two controls
Section titled “The two controls”Surface — a Front / Back / Both dropdown. It chooses which coating you
are designing and which stack the optimizer is allowed to move. When Both
is selected, a Symmetric (back = front) sub-checkbox appears; ticking it
links the back coating to an exact mirror of the front, so both sides are
optimized together as one identical stack.
Ignore other side — a checkbox. When checked, the design is evaluated as the active surface alone, sitting on a semi-infinite substrate with no back-surface reflection — the standard idealization for designing a single coating. When unchecked, the design is evaluated as the whole physical part: front coating, finite substrate, and back coating, combined together. The checkbox is disabled for Both, because two real coatings are always evaluated as the full system.
A new design starts at Front + Ignore other side — you design one front coating against air and a semi-infinite substrate, which is the most common starting point.
How the two controls combine
Section titled “How the two controls combine”The Front and Back tabs in the layer table are always present, but the ignored side’s tab goes inactive — you cannot edit a coating you have told the program to ignore. Its layers stay in the design, dormant, and return the moment you clear the checkbox.
| Surface | Ignore other side | Front tab | Back tab | Optimizes | Evaluates |
|---|---|---|---|---|---|
| Front | off | active | active | front | TOTAL |
| Front | on (default) | active | inactive | front | FRONT only |
| Back | off | active | active | back | TOTAL |
| Back | on | inactive | active | back | BACK only |
| Both | — (disabled) | active | active | both | TOTAL |
| Both + Symmetric | — (disabled) | active | inactive (= front) | both, linked | TOTAL |
“Front, don’t ignore” and “Both” both evaluate the total part — the only difference is what the optimizer is free to move. With Front selected the optimizer moves only the front coating (any back coating is included but fixed); with Both it also frees the back stack.
The badges
Section titled “The badges”Because the two controls live only in the Design Editor, every other window shows what it is doing as a read-only badge:
Eval: FRONT / BACK / TOTAL— appears in Optical Evaluation, Integral Values, the Specification, Color, Monte-Carlo, Systematic Deviations, Layer Sensitivity, the Variator, Inhomogeneities and Roughness/Scattering. It is the same value in all of them.Optimize: FRONT / BACK / BOTH / BOTH (sym)— appears additionally in the optimizer windows (Refinement, Needle Variation, Gradual Evolution, Manual Needle) to show which coating is being moved.
How the substrate is handled
Section titled “How the substrate is handled”| Ignore other side | Substrate model | Back surface |
|---|---|---|
| Checked (single surface) | Semi-infinite — light exits into the substrate and never returns | None — no back-surface reflection |
| Unchecked (total) | Finite and incoherent — internal reflections combine as intensities | Real: the bare-substrate reflection, or the back coating if one exists |
A single-surface coating designed with “Ignore other side” is evaluated exactly as the coating in isolation — the correct idealization for that task — while clearing the checkbox folds in the real back surface to show what the finished, two-sided part actually does.
These settings are stored on the design, so they save with the project and a design reopens in the mode it was built in. Integral Values is a whole-part figure and follows these modes too. The per-surface windows — group delay, electric field, ellipsometry, the admittance diagram and the refractive-index profile — instead carry their own Front / Back control, since each shows a single coating on the substrate in isolation. The refractive-index profile adds a Total option that lays the front coating, substrate and back coating out as one continuous structural (n, k vs depth) profile.
References
Section titled “References”- H. A. Macleod, Thin-Film Optical Filters, 5th ed., §2.6.4 (combining a coated substrate’s two surfaces incoherently).