# Optical material library

`GSIM_MATERIAL_CARDS` contains the built-in fallback optical models. Project and PDK cards take precedence.

## Built-in cards

### Silicon

| Lookups | Supported values | Defaults | Paper |
| --- | --- | --- | --- |
| `Si` (default), `Si-Salzberg` | `λ = 1.357–11.04 µm`<br>`T` fixed | `T = 299.15 K` | [Salzberg and Villa 1957](<https://doi.org/10.1364/JOSA.47.000244>) |
| `Si-Li-293K` | `λ = 1.2–14.0 µm`<br>`T = 100–750 K` | `T = 293 K` | [Li 1980](<https://doi.org/10.1063/1.555624>) |

### Silicon nitride

| Lookups | Supported values | Defaults | Paper |
| --- | --- | --- | --- |
| `SiN` (default), `SiN-Luke` | `λ = 0.310–5.504 µm` | — | [Luke et al. 2015](<https://doi.org/10.1364/OL.40.004823>) |

### Fused silica

| Lookups | Supported values | Defaults | Paper |
| --- | --- | --- | --- |
| `SiO2` (default), `SiO2-Malitson` | `λ = 0.21–6.7 µm`<br>`T` fixed | `T = 293 K` | [Malitson 1965](<https://doi.org/10.1364/JOSA.55.001205>) |

### Lithium niobate

| Lookups | Supported values | Defaults | Paper |
| --- | --- | --- | --- |
| `LN` (default), `LiNbO3-Zelmon` | `λ = 0.4–5.0 µm`<br>`axis = o or e`<br>`T` fixed | `T = 21 °C` | [Zelmon et al. 1997](<https://doi.org/10.1364/JOSAB.14.003319>) |
| `LiNbO3-MgO5-Gayer` | `λ = 0.5–1.62 µm`<br>`axis = o or e`<br>`T = 20–100 °C` | `T = 24.5 °C` | [Gayer et al. 2008](<https://doi.org/10.1007/s00340-008-2998-2>) |

## Refractive index

Curves span each model's full wavelength validity and use its default temperature.

```python
from gsim.common.materials import resolve_material_snapshot

snapshot = resolve_material_snapshot("Si", wavelength_um=1.55)
print(snapshot.refractive_index)
```

Lookup is case-sensitive. A project card with the same name replaces that fallback.

## Analytic PDK cards

Project cards can use `pdk_schema.AnalyticDispersion` with scalar `n` or `n_squared` output, including AN800's modified Sellmeier equations. The resolver converts the simulation wavelength to each declared input unit (`um`, `nm`, or `m`), evaluates the stored equation and parameters, and enforces the card's wavelength validity. These models produce a lossless snapshot with zero extinction coefficient.

Analytic inputs other than wavelength and `eps_real` output are not supported by the scalar index resolver. Invalid or non-real equation results raise `MaterialModelError`; out-of-range wavelengths raise `WavelengthOutOfRangeError`.