Refractive index of K (Potassium)

import lightsmith as ls

# K (Potassium): Monin and Boutry 1974: n,k 0.254–0.620 µm; 195 K
k = ls.fetch_refractiveindex("main", "K", "Monin", ref="c5c2f188e848453def5970e347399d653df2ffc2")
print(k.range_nm)  # (253.6, 620) nm
eps = k.eps([397])  # complex permittivity

import json, urllib.request
import lightsmith as ls

url = "https://materials.lightsmith.dev/v1/datasets/ds_d8b680aea8cd/lightsmith"
k = ls.Tabulated.model_validate(json.load(urllib.request.urlopen(url)))
print(k.source)  # citation and provenance travel with the data

# ... load k as above, then:
sim = ls.Simulation(
    particles=[ls.Particle(shape=ls.Sphere(radius_nm=50), material=k)],
    medium_index=1.0,
    wavelengths=ls.WavelengthRange(start_nm=400, stop_nm=620, num=81),
)
res = ls.solve(sim)  # exact Mie for a sphere
print(res.q_ext)     # extinction efficiency at each wavelength