Refractive index of He (Helium)

import lightsmith as ls

# He (Helium): Cuthbertson and Cuthbertson 1936: n 0.275–0.546 µm
he = ls.fetch_refractiveindex("main", "He", "Cuthbertson", ref="c5c2f188e848453def5970e347399d653df2ffc2")
print(he.range_nm)  # (275.3, 546.2) nm
eps = he.eps([388])  # complex permittivity

import json, urllib.request
import lightsmith as ls

url = "https://materials.lightsmith.dev/v1/datasets/ds_db9367ad91f0/lightsmith"
he = ls.Tabulated.model_validate(json.load(urllib.request.urlopen(url)))
print(he.source)  # citation and provenance travel with the data

# ... load he as above, then:
sim = ls.Simulation(
    particles=[ls.Particle(shape=ls.Sphere(radius_nm=50), material=he)],
    medium_index=1.0,
    wavelengths=ls.WavelengthRange(start_nm=400, stop_nm=546, num=81),
)
res = ls.solve(sim)  # exact Mie for a sphere
print(res.q_ext)     # extinction efficiency at each wavelength