Physical and numerical conventions

Wavelength and optical constants

PyOptik accepts vacuum wavelength quantities. Always attach units—for example 1550 * ureg.nanometer—to avoid ambiguity. Bare numeric inputs are retained for compatibility and interpreted as metres.

The complex refractive index uses the convention N = n + i k: n is the real refractive index and k is the non-negative extinction coefficient. The convenience methods material.n(wavelength), material.k(wavelength), material.relative_permittivity(wavelength), and material.absorption_coefficient(wavelength) expose common derived values. The relative permittivity is N² and the intensity absorption coefficient is α = 4πk / λ.

Interface and multilayer power

Fresnel and thin-film calculations use the same n + i k convention. reflectance, transmittance, and absorptance are fractions of normal optical power flux and satisfy R + T + A = 1 up to numerical precision. The complex reflection_amplitude and transmission_amplitude retain phase information. Multilayer results use the characteristic-matrix field convention; power fractions are usually the portable quantities when comparing different polarization bases.

Dispersion and group delay

compute_group_delay_dispersion returns conventional frequency-domain GDD, dτ_g/dω = d²β/dω² × length. Its units are time squared (typically fs²). compute_group_delay_wavelength_slope is deliberately separate because it returns dτ_g/dλ, a wavelength-space derivative with different units.

Interpolation and validity ranges

Tabulated materials use linear interpolation by default. Pass interpolation="pchip" to MaterialPage.load or TabulatedMaterial for monotonic piecewise-cubic interpolation without overshoot. Both methods use linear endpoint extrapolation when out_of_range="warn"; set out_of_range="raise" for strict validity enforcement, or out_of_range="clip" to evaluate at the nearest source boundary.

Comparisons at validity endpoints tolerate floating-point round-off introduced by unit conversion. Thus, for example, 600 nm remains inside a source range ending at 0.6 µm.

Provenance and conditions

Every loaded material provides material.provenance. It contains the source reference, upstream catalog ID and URL when available, source path, stated wavelength range, and the upstream YAML CONDITIONS and COMMENTS fields. Use it when recording simulation inputs or preparing results for publication.

page = catalog.get("specs/SCHOTT-optical/N-BK7")
material = page.load()
print(material.provenance)