Material Editor

The Material Editor is where you manage every refractive-index source TFStudio knows about. Each material provides a refractive index n(λ) and an extinction coefficient k(λ); absorbing materials have k > 0. Every dropdown in the app that asks you to pick a material reads from here.

Materials are grouped into catalogs by source:

Catalog	Source	Editable
Built-in	A curated set of 16 common optical materials.	Read-only
AGF	Zemax .agf files placed in your TFStudio data folder’s Materials subfolder.	Via the file
User	Materials and catalogs you create inside TFStudio.	Yes
RefractiveIndex	Materials you import from the refractiveindex.info database.	Yes

The left panel holds a catalog selector, a search box, and the material list; the right panel shows the selected material on two pages, n & k and Mechanical. Built-in and AGF materials show read-only details (properties, dispersion formula, tabulated data, and an n/k chart); user and imported materials open in an editable form. The name, id, colour and wavelength range stay above the two pages, since they identify the material whichever page is open.

Settings

Catalog selector: choose a single catalog or All. The selector shows each catalog’s material count, and beneath it sit the actions for managing the selected catalog.

Search: filter the list by name (case-insensitive). The filter respects the catalog you have selected.

Import AGF: load a Zemax .agf glass file as a new catalog. AGF files store internal transmittance versus wavelength; TFStudio converts that to k(λ) automatically. AGF files you place in your TFStudio data folder’s Materials subfolder are also picked up automatically when the app starts. A glass whose dispersion formula number is not one TFStudio evaluates is left out of the catalog, and the import message names it. A file picked up at startup has no window to report in, so import it with Import AGF to see which glasses were left out.

Import material files: load materials written by other coating programs, any mix of them in one pick:

Program	Files
TFCalc	.mat from the MATERIAL and SUBSTRAT folders
Essential Macleod	.tfx from a materials database folder, or .mtx written by File → Export → Material
OptiLayer	.lm and .sub

The import dialog lists every material it read with its program and data type (table with its point count, or the formula in the program’s own name), and previews the highlighted one: formula and coefficients or the table rows, and an n/k chart. Untick what you do not want, choose the catalog to add to, or create a new one.

TFCalc and Essential Macleod files do not record their wavelength unit. The dialog assumes nanometres, reads the unit from an Essential Macleod database’s own settings when the .tfx file sits in its database folder, and has a switch to micrometres for when the preview shows the curve in the wrong place.

Formula materials keep their formula where TFStudio has the same form. The TFCalc forms it lacks (Hartmann, Drude, and every k formula) are sampled onto a table over the range the file states. An Essential Macleod internal-transmittance table has no equivalent here and is left out; the k column is imported as it is. The compressed files of the Essential Macleod materials library cannot be read: open such a material in Essential Macleod and save it into your database first.

A table point with k below zero is imported as written and marked in the dialog, with the count in the preview. Essential Macleod’s own materials hold a few such points, and so do some refractiveindex.info tables; they are the residue of the fit that produced the table. A negative extinction coefficient would be gain, so every calculation reads k = 0 at such a point, and the n,k grid of the Material Editor marks the row.

Browse RII: open the refractiveindex.info browser to pick from the online database (an internet connection is needed the first time you fetch a material). The material is added to your chosen user catalog and then lives locally.

New Catalog: create an empty user catalog to organize your own materials.

Duplicate: copy the selected catalog (from any source) into a new, editable user catalog. Copy to catalog copies a single material into a user catalog, which is the way to make an editable variant of a read-only material.

Creating a material

Open a user catalog and choose New material. The n & k page holds the optical data; pick a data type there:

1. Tabular: paste or type a λ, n, k table. You can paste directly from a spreadsheet (Ctrl+V), and the grid supports keyboard navigation, sorting and per-cell editing.
2. Formula: choose a dispersion formula (Sellmeier, Cauchy, Conrady, Schott, Herzberger and other standard forms), enter its coefficients, and optionally add a λ, k table for absorption. The formula is rendered in full so you can confirm the convention. The Cauchy and general Sellmeier forms take as many terms as you add; a term left at zero is dropped when the material is saved.

A live n/k chart updates as you edit, and the wavelength range you set bounds where the material is valid and the span the chart shows. Under the chart, type a wavelength to read n and k there, and a sampled table lists the curve’s numbers. The same probe and table sit under the chart of a read-only material. Where a formula has no finite value, the preview gives no n.

A material TFStudio cannot compute is never given a stand-in index. A formula it has no evaluator for, or a table with no row that holds both a wavelength and an n, makes the material unavailable: a design that uses it lists it among its unavailable materials, and calculations are blocked until you replace it. Saving the design keeps such a definition as it was written, so nothing in it is lost.

Between the table points

A table says nothing about the wavelengths between its points, so every tabulated n and k column carries a rule for reading it there. The control under the grid offers two:

• Shape-preserving cubic (PCHIP), the default for a new material. The curve passes through every supplied point and stays inside the values of each bracketing pair, so a non-negative k table cannot acquire optical gain from interpolation overshoot, and it has a slope everywhere, which is what phase and dispersion calculations need.
• Linear, straight lines between the points. This is how Essential Macleod and TFCalc evaluate a table, and a material imported from either keeps it, so a design imported with such materials reproduces the numbers it produced there. The slope changes abruptly at each point; the GD/GDD window breaks its curves there rather than draw through the jump.

The rule belongs to the material, not to a window, so it reaches every calculation made with it, travels with a material embedded in a design, and is what the two programs disagree on between measured points. Neither rule adds information the table does not hold: where the answer depends on the curvature of n(λ) between measurements, a smooth dispersion fit is the honest model. Outside the tabulated range both rules hold the nearest endpoint value constant.

Smooth dispersion fit

An editable tabular material can store an explicit smooth fit for calculations that need higher derivatives. Transparent materials can use Cauchy or a one- to three-term Sellmeier model for n; k uses a non-negative Urbach form when the table contains enough positive values, otherwise it remains zero. Metals can use a coupled Drude or Drude-Lorentz dielectric model, which fits n and k together.

The fit covers its own wavelength range, set in Fit from and Fit to and separate from the validity range at the top of the form. It starts at the range the design is evaluated over, where the table reaches that far, because that is where the fit has to be right; outside the fit range the table itself is read. Where the fit ends inside the table, n and k step from the fit to the table by the fit’s own residual there. The fit panel names that step at each end, and the GD/GDD and Material Dispersion windows break their curves at it rather than draw through it. A fit that ends at the table’s first or last row has no step. The range is stored with the fit and comes back the next time the material is opened.

A range covering more than a decade of photon energy is reported as such. No single model holds free-electron behaviour, an interband edge and the transparent region at once, so a fit over all of it is poor everywhere, and the range the design is evaluated over is offered in its place with the residual it reaches.

Choose Fit or Refit to calculate it. TFStudio shows RMS and maximum residuals for both n and k, plus a residual plot. Inspect those errors before using the model. A Cauchy or Urbach fit to the table also shows each coefficient with its standard error. For the metal models it also reports a parameter left on one of the model’s own limits, and an oscillator that changes n across the range by less than the residual: neither is a measurement of the material, and the residual alone does not say so. The fit is not created silently. It is stored on the material, travels with an embedded user material, and is removed automatically when its source table changes. Built-in materials remain read-only; copy one to a user catalog before fitting a different representation.

Mechanical constants

The Mechanical page holds what a material is besides its dispersion.

Constant	Unit	What it is
Young’s modulus	GPa	Stiffness under tension.
Poisson’s ratio		Sideways contraction while it stretches.
Linear expansion	ppm/K	How much it grows per kelvin.
dn/dT	ppm/K	How the refractive index moves with temperature.
Intrinsic stress	MPa	The stress a film of it is deposited with, tensile positive.
Reference temperature	°C	The deposition temperature that intrinsic stress refers to.
Surface energy	J/m²	The energy a fresh surface costs, which is what a crack or a delamination pays for.

Both temperature coefficients are entered in ppm/K, the way catalogs print them: an expansion coefficient of 0.00000055 per kelvin is typed as 0.55.

Every box stands on its own and any of them may be left empty, which means unknown rather than zero: a material whose stress you measured but whose modulus you never looked up carries the stress alone. The constants are part of the material, so they follow it into a user catalog, into a copy, and into a design file that embeds it. A glass imported from an AGF catalog arrives with its expansion coefficient, Young’s modulus and Poisson’s ratio already filled in, which is what those files carry.

How to read it

For a built-in or imported material, the n/k chart shows the real index n (left axis) and, when present, the extinction coefficient k (right axis, dashed). The properties panel lists the d-line index, Abbe number, density and wavelength range when the source provides them, and the dispersion formula and coefficients when the material is formula-based. A material with a flat, zero k is non-absorbing across the plotted range. Its Mechanical page lists the constants the catalog stated and nothing else; a material that states none says so.

Catalogs are saved to your TFStudio data folder’s Materials subfolder and persist between sessions, so an imported or hand-built material is available the next time you open the app.

References

• M. N. Polyanskiy, refractiveindex.info (public-domain dispersion data).
• F. N. Fritsch and J. Butland, “A Method for Constructing Local Monotone Piecewise Cubic Interpolants,” SIAM Journal on Scientific and Statistical Computing 5, 300-304 (1984).
• A. D. Rakić et al., “Optical properties of metallic films for vertical-cavity optoelectronic devices,” Applied Optics 37, 5271-5283 (1998), doi:10.1364/AO.37.005271.
• Beer–Lambert relation for extinction from internal transmittance: k(λ) = −λ / (4π d) · ln τ_int(λ).