Layer stacks¶

kind: "layer_stack", model lightsmith.problems.LayerStackProblem. A planar multilayer between a semi-infinite superstrate and a semi-infinite substrate. Computes reflection, transmission and absorption against wavelength, angle and polarisation.

Fields¶

Field	Meaning
`superstrate`	The incidence medium, a material
`layers`	`Layer(thickness_nm, material, coherent=True)`, listed from the superstrate side to the substrate side. Set `coherent=False` for thick slabs, such as a 1 mm substrate.
`substrate`	The exit medium, a material
`wavelengths`	Vacuum wavelengths in nm
`angles_deg`	Angles of incidence in the superstrate (default `[0]`)
`polarizations`	Any of `"s"` and `"p"` (default both)
`options`	Per-method solver options

Result¶

SpectrumResult:

r, t and a per polarisation, indexed [angle][wavelength];
r_amplitude and t_amplitude as (real, imaginary) pairs, when every layer is coherent;
provenance and warnings.

SpectrumResult.difference(other) gives the maximum and RMS differences between two spectra on the same grids.

Solvers¶

auto order: TMM → RCWA → FDTD.

TMM is exact and fast, handles incoherent layers, and is differentiable.
RCWA treats an unpatterned stack as a single-harmonic problem.
FDTD handles normal incidence only.

Example¶

import lightsmith as ls
from lightsmith.problems import Layer, LayerStackProblem

bragg = LayerStackProblem(
    superstrate=ls.ConstantIndex(n_real=1.0),
    layers=[Layer(thickness_nm=600 / 4 / n, material=ls.ConstantIndex(n_real=n))
            for _ in range(10) for n in (2.3, 1.45)],
    substrate=ls.ConstantIndex(n_real=1.52),
    wavelengths=ls.WavelengthRange(start_nm=450, stop_nm=800, num=351),
)
res = ls.solve(bragg)