Materials: responsibilities and callers#

The material interface describes optical properties. A material supplies real refractive index n(wavelength, **kwargs) and dimensionless extinction coefficient k(wavelength, **kwargs), with wavelength in micrometers. The propagation model controls travel through the medium; surface interaction models control refraction, reflection and coatings. Neither belongs in a dispersion equation. Spatial GRIN propagation remains a separate, unimplemented feature.

Choosing and constructing a material#

Public material responsibilities#
Type	Responsibility and state owner	Construction and principal callers
`BaseMaterial`	Property interface, subclass registry, propagation attachment, cache context and native deserialization dispatch. No optical equation.	Subclassed by material implementations; queried by all runtime consumers.
`IdealMaterial`	Constant index and extinction in live backend arrays. Index 1 is air only when extinction is zero.	Constructed by users, `MaterialFactory` and file readers for constant media; used in tracing and index optimization.
`AbbeMaterial`	d-line index/Abbe specification. The selected polynomial or Buchdahl model owns the live parameters and prediction equation.	Users, glass optimization and readers with index/Abbe data. Polynomial evaluation is limited to 0.38–0.75 µm; Buchdahl has no declared limits.
`AbbeMaterialE`	e-line index/Abbe specification using the e-line Buchdahl model. Shares parameter delegation with the d-line wrapper.	Users and readers with e-line specifications; the same tracing and persistence callers as `AbbeMaterial`.
`MaterialFile`	Existing refractiveindex.info YAML adapter. Owns live coefficients, sampled arrays and thermal fields, and retains filename-based JSON. Shared helpers evaluate its equations and interpolation.	Users with a YAML file and the `Material` catalog wrapper. Its normal table evaluation defaults to endpoint clamping, including one-sample tables; `bounds="raise"` opts into strict table support.
`Material`	Catalog resolution, name/reference identity and lookup provenance on top of `MaterialFile`. It does not implement another dispersion engine.	`MaterialFactory`, `MaterialCatalog.get`, named-glass file readers, glass selection and user code.
`DataMaterial`	Owns an immutable, spatially uniform sampled or analytic definition and optional independent extinction table. Requires no file, catalog or registration. Native JSON contains the complete optical definition and copied metadata.	`from_samples`, `from_coefficients` or a native definition dictionary; OSLO sampled-index input and explicit material overrides. Used by the same property, plotting and persistence callers as other materials.

AbbeModel is a prediction interface, not a material. AbbePolynomialModel, BuchdahlDModel and BuchdahlEModel own their equations and reference-line conventions. Fresh predictions derive coefficients from current parameters; the wrappers expose those exact parameters and provide material persistence.

MaterialSpec and MatchPolicy describe catalog lookup choices. MaterialRegistry owns discovery, registered YAML sources and resolution; MaterialCatalog is its catalog-scoped browsing facade. These are not optical evaluators. MaterialFactory converts surface specifications into material instances: an existing material is accepted directly, and a dictionary there continues to describe a lookup specification. Restore an inline native object with BaseMaterial.from_dict before passing it to a surface.

Owned data and persistence#

from optiland.materials import BaseMaterial, DataMaterial

measured = DataMaterial.from_samples(
    [0.4, 0.6, 0.8], [1.6, 1.55, 1.5], name="measured glass",
    extinction={
        "kind": "tabulated_k",
        "wavelengths_um": [0.45, 0.75],
        "values": [0.001, 0.002],
    },
    metadata={"source": "laboratory measurement"},
)
analytic = DataMaterial.from_coefficients(
    "formula 2", [0, 1.03961212, 0.00600069867,
                  0.231792344, 0.0200179144, 1.01046945, 103.560653],
    wavelength_range=(0.3, 2.5), name="analytic example",
)
restored = BaseMaterial.from_dict(measured.to_dict())
assert restored.definition == measured.definition

The definition contains a dispersion tagged as tabulated or formula, an optional extinction tagged as tabulated_k, and reserved thermal: null. Formula identifiers are formula 1 through formula 9, using the existing refractiveindex.info conventions. A formula remains analytic; it is never replaced with fitted or sampled indices. Negative finite indices are permitted in the generic material interface. Import/export adapters enforce their own format’s physical restrictions.

Sample arrays are sorted together and require at least two distinct positive wavelengths. All optical data must be finite; extinction must be nonnegative. Each table rejects queries beyond its own support by default. Missing extinction means zero at all finite positive wavelengths. Formula bounds are optional and enforced when supplied. Scalar evaluation returns a one-element array; array queries keep their shape and Torch wavelength gradients. Imported coefficients are constants, not trainable parameters: create a replacement definition to change them.

The frozen definition and its tuple fields cannot be edited. Input containers, serialized containers and finite JSON metadata are copied; metadata and display names do not affect optical evaluation. BaseMaterial.from_dict dispatches the class and restores the registered propagation model. Existing public material JSON formats continue to work; there are no aliases for earlier unreleased material prototypes.

Choosing a table bounds policy#

DataMaterial accepts a keyword-only bounds="raise" or bounds="clamp" on its constructor and both factories. MaterialFile and its catalog wrapper Material expose the same option with "clamp" as their existing default. The option applies to every tabulated property of the material, with each n/k table using its own wavelength interval. It does not change the stored samples or the support reported by spectral_range.

from optiland.materials import DataMaterial, Material, MaterialFile

measured = DataMaterial.from_samples(
    [0.4, 0.8], [1.6, 1.4], bounds="clamp",
)
assert measured.n(0.9).item() == 1.4
strict_file = MaterialFile("measurements.yml", bounds="raise")
strict_catalog = Material("N-BK7", catalog="schott", bounds="raise")

Clamping holds the nearest endpoint value. It is an explicit assumption about unknown dispersion or absorption outside the supplied interval, not additional measurement data. The clamped interpolation’s wavelength derivative is zero outside the table; later thermal corrections can still depend on wavelength. Gradients with respect to live file-table endpoint values remain available. The default exception for owned data prevents silently tracing with this assumption. A strict one-sample file table accepts only its recorded wavelength; clamping makes it constant.

The policy is read-only after construction, is part of material cache state and is written as bounds in native material JSON. Construct a replacement to choose another policy. Old public MaterialFile/Material JSON without this field still loads with clamping, and new saves record it explicitly. This allows applications to opt into strict table evaluation now and retain their chosen behavior if a later breaking release changes the file-material default.

Analytic equations are independent of table interpolation: a declared DataMaterial formula range is always enforced, while MaterialFile keeps its existing analytic extrapolation behavior. On from_coefficients, the bounds option therefore affects only an optional tabulated extinction curve. Missing extinction remains the documented zero assumption. Invalid/nonpositive DataMaterial wavelengths still fail even with clamping enabled.

OSLO can preserve owned index samples but cannot encode this explicit clamping choice. Its writer rejects clamped DataMaterial objects before replacing the destination; use native JSON to retain the policy. Catalog-name exports in external formats retain the destination program’s evaluation conventions.

Shared implementation ownership#

dispersion.py owns all nine formula equations and coefficient arity checks. Both DataMaterial and MaterialFile call it.
buchdahl.py owns the Buchdahl coordinate transform and polynomial evaluation for any order. The existing three-term Abbe models call it; higher-order models can reuse it with their own coefficients. Reference wavelengths, alpha, fitted constants, validity limits and coefficient generation belong to the individual model, not this algebra module.
spectral.py owns finite sample validation and linear interpolation, with an explicit bounds policy chosen by the caller. It preserves the constant single-sample behavior required by existing YAML data.
definition.py owns private immutable records and native definition validation/encoding. It contains no file access, backend arrays or cache.
rii.py decodes YAML spectral blocks to plain intermediate records. MaterialFile binds those values to its existing live arrays; it does not retain a second immutable copy of mutable optical state.
BaseMaterial owns property caching. Mutable built-ins report all live optical state; DataMaterial reports its immutable definition and bounds policy. New custom subclasses evaluate uncached unless they explicitly implement _cache_state. Graph-bearing queries bypass result caching.

Runtime and persistence callers#

Consumer boundaries#
Consumer	Contract and responsibility
Surface groups and paraxial/real ray tracing	Query index at the ray wavelength. Material ownership is independent of whether rays are traced sequentially or through the nonsequential adapter.
Interaction models and thin-film calculations	Query n and k, then own complex-index conventions, Fresnel coefficients, layer interference and polarization. Materials do not implement coatings.
`HomogeneousPropagation`	Advances rays and uses extinction for attenuation, and owns propagation distance units and absorption conversion.
`NSQMaterial`	Adapts a material to nonsequential tracing and attaches a surface BSDF; it delegates optical dispersion instead of duplicating its equations.
Optimization material variables	Update live Ideal/Abbe parameters or choose catalog glass. Owned imported definitions are constant data and are replaced as complete definitions.
Native JSON	Uses `to_dict` and `BaseMaterial.from_dict`. Data definitions are self-contained; file/catalog materials retain their public reference format.
OSLO reader/writer	Reader constructs sampled `DataMaterial` when distinct saved indices are present. Writer preserves homogeneous positive n tables with no extinction; other owned definitions require native JSON. The label is never interpreted as a catalog reference.
Zemax and CODE V writers	Reject `DataMaterial` before opening the destination. An n/Abbe fit or a guessed glass name would lose the imported definition. All three external writers preflight both incident and outgoing media for custom propagation before air, catalog, model-glass or mirror shortcuts. This check does not implement spatial-material export.
Plotting and information display	Use `display_name` and `spectral_range('n'/'k')`. `plot_nk` intersects requested and known limits and requires an explicit range if none are known. It plots in µm and converts to host arrays only at the display boundary.

Adding catalog transmission/thermal data or new file encodings requires a separate feature with its own physical validation and persistence tests. Material temperature/pressure keywords are not automatically connected to the global Optic environment; that caller-level change is outside this material rework.

Extending material models#

A fitted glass model with live index, Abbe number or partial-dispersion parameters is a BaseMaterial implementation (or a prediction strategy behind a material wrapper). It is not an immutable imported data definition. Reuse buchdahl_coordinate(wavelength, reference_wavelength, alpha) and evaluate_buchdahl(index, coefficients, omega) for Buchdahl models. Pass coefficients in increasing power order, starting with the linear term. Different fits can have different orders and reference conventions without sharing regression assets or becoming the same optical model.

Derive coefficients from the current parameters during evaluation; retaining a derived tensor graph across optimizer steps or backward calls gives stale values or invalid gradients. Reuse immutable regression data separately from that derived state. Use backend operations and preserve parameter and wavelength gradients. A new subclass is uncached by default; opt in only with a complete _cache_state including every optical parameter and model choice. Caching does not refresh coefficients stored by the subclass itself.

Serialize the model’s defining parameters in to_dict alongside super().to_dict(). Its from_dict reconstructs those parameters; BaseMaterial.from_dict restores propagation centrally. Do not serialize derived coefficients as a second authority. Native loading and GUI background workers must import the material class so its registry entry exists. GUI undo and document replacement use the same native persistence contract.

Provide display_name for labels and spectral_range('n'/'k') for known validity limits, validating the property name through the base contract. Information displays use this label for unregistered material families; explicit formatter registrations and a configured default still take precedence. Unknown limits remain None; plotting then requires an explicit range. Consumers must not infer catalog identity from a display label, or assume an abbe member is numeric: BaseMaterial.abbe() is a method while the Abbe wrappers expose a live parameter. Callers needing a spectral-line quantity should evaluate n at the stated wavelengths. An optimization variable owns its choice of model and must preserve all independent model parameters when updating one of them. Import/export mappings need explicit, tested semantics; sharing an equation does not make different fitted models interchangeable.

A future spatial material is another BaseMaterial implementation. It can compose an existing material as its homogeneous spectral background, without forcing its field or propagation controls into DataMaterial.definition. Keep position/environment arguments in n/k(..., **kwargs) and require the position needed by the optical law. In an opted-in cache, spatial context must participate in the key even when all wavelengths are equal.

This extension point does not make tracing, paraxial analysis, wavefront launch phase, drawings or coatings position-aware. A GRIN implementation must update those callers or reject unsupported use, and define medium coordinates, boundary events, index/gradient consistency and a single owner of optical-path and attenuation integration. Custom propagation must remain explicit so homogeneous-only exporters can reject it. A spatial law attached to the default homogeneous propagator is not a supported GRIN configuration.