Real Materials

Use wavelength-dependent refractive indices from DiffTMM's bundled catalogs instead of constant numbers. The Material class supplies dispersive n(λ) and absorptive k(λ) data, looked up by name and passed directly to any solver.

Notebook: 3_real_materials.ipynb

Inspect a material's dispersion

Material(name).ior(wvln) returns the complex refractive index at the given wavelengths (μm) — real part n, imaginary part k:

import torch
from difftmm import IsotropicFilmSolver, Material, list_materials

device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
print(len(list_materials()), "known materials")

wvln = torch.linspace(0.40, 0.80, 100, device=device)
for name in ["SiO2", "TiO2", "Ag"]:
    n = Material(name, device=device).ior(wvln)   # complex tensor
    print(name, "n@550nm =", n[27].real.item(), "k@550nm =", n[27].imag.item())

SiO₂ is a low-loss dielectric, TiO₂ a high-index dielectric, and Ag a metal with a large imaginary index in the visible.

$Refractive index n(λ) and extinction coefficient k(λ) for SiO₂, TiO₂, and Ag across the visible band$

Anti-reflection coating

Pass material names straight into the solver — they're auto-wrapped in Material. Here a two-layer TiO₂/SiO₂ AR coating on an N-BK7 substrate:

solver = IsotropicFilmSolver(
    mat_in="air",
    mat_out="N-BK7",
    mat_ls=["TiO2", "SiO2"],
    thickness_ls=[0.06, 0.10],     # 60 nm / 100 nm
    device=device,
)

wvln  = torch.linspace(0.45, 0.75, 60, device=device)
theta = torch.tensor([0.0], device=device)            # normal incidence
ts, tp, rs, rp = solver.simulate(theta=theta, wvln=wvln)

R = (rs.abs() ** 2).squeeze()      # broadband reflectance

Broadband reflectance of the Air | TiO₂ | SiO₂ | N-BK7 anti-reflection coating

Surface plasmon resonance

A metal layer in the Kretschmann configuration shows a sharp p-polarized reflection dip as surface plasmons are excited — driven by silver's large imaginary refractive index. Sweep the angle at 633 nm through a 50 nm silver film on a glass prism:

solver = IsotropicFilmSolver(
    mat_in=1.52,            # glass prism
    mat_out="air",
    mat_ls=["Ag"],
    thickness_ls=[0.05],     # 50 nm Ag
    device=device,
)

theta = torch.linspace(0.7, 1.2, 200, device=device)   # ~40-70 deg, radians
wvln  = torch.tensor([0.633], device=device)
_, _, _, rp = solver.simulate(theta=theta, wvln=wvln)

R_p = (rp.abs() ** 2).squeeze()    # reflection dip marks the plasmon resonance

Kretschmann surface plasmon resonance: a sharp p-polarized reflection dip vs. angle at 633 nm through a 50 nm silver film

This SPR calculation is one of the cases DiffTMM is validated against the reference NumPy TMM library. See 3_real_materials.ipynb for the full plots.