lsurf.materials.cauchy_refractive_index

lsurf.materials.cauchy_refractive_index(wavelength, A=1.458, B=0.00354, C=0.0)

Compute refractive index using Cauchy equation.

The Cauchy equation is a simple empirical dispersion formula, valid in regions of normal dispersion (away from absorption bands).

Parameters:

• wavelength (float) – Wavelength in meters.

• A (float) – Constant term (refractive index at infinite wavelength). Default is for typical crown glass.

• B (float) – First-order dispersion coefficient in μm². Default is for typical crown glass.

• C (float) – Second-order dispersion coefficient in μm⁴. Default is 0.

Returns:

n – Refractive index at given wavelength.

Return type:

float

Notes

Cauchy equation:

n(λ) = A + B/λ² + C/λ⁴

where λ is in micrometers.

Suitable for glasses and transparent materials in visible range. Less accurate than Sellmeier near absorption edges.

References

[1]

Cauchy, A.-L. (1836). Bull. Sci. Math., 14, 6-10.

Examples

>>> n_550nm = cauchy_refractive_index(550e-9, A=1.5, B=0.004)
>>> print(f"n = {n_550nm:.4f}")