API Reference

DiffTMM exposes a small, focused API: a set of film solvers that compute the optical response of a multi-layer stack, plus a Material class that supplies wavelength-dependent refractive indices.

Every solver follows the same pattern — construct it with the stack geometry (incident medium, interior layers, exit medium, thicknesses), then call simulate(theta, wvln) to get the Fresnel coefficients:

solver = Solver(mat_in=1.0, mat_out=1.52, mat_ls=[2.1, 1.46], thickness_ls=[0.08, 0.12])
ts, tp, rs, rp = solver.simulate(theta, wvln)   # shape (batch, n_wvlns, n_angles)

All thicknesses are in micrometers (μm), angles in radians, and wavelengths in μm.

• Isotropic Solver

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  IsotropicFilmSolver — the fast 2×2 transfer matrix method for isotropic stacks. The default choice for most coatings (~190× faster than NumPy TMM).

  Isotropic Solver

• Anisotropic Solver

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  FilmSolver (alias AnisotropicFilmSolver) — the general 4×4 transfer matrix method for birefringent media, with per-axis (nx, ny, nz) layers.

  Anisotropic Solver

• Incoherent Solver

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  IncoherentIsotropicFilmSolver — marks layers coherent/incoherent so thick substrates don't produce unphysical Fabry–Perot ripples.

  Incoherent Solver

• Materials

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  Material — wavelength-dependent complex refractive index from bundled glass (Sellmeier) and thin-film (n+k) catalogs, looked up by name.

  Materials

Output convention

The coherent solvers (isotropic, anisotropic) return complex amplitude coefficients ts, tp, rs, rp — square the magnitude for power (T = |t|², R = |r|²). The incoherent solver returns real power coefficients Rs, Rp, Ts, Tp directly, because incoherent calculations discard phase by design.