Python interface to RefractiveIndex database

The original database
https://github.com/polyanskiy/refractiveindex.info-database

Installation

pip install refractiveindex

Usage

import numpy as np
from refractiveindex import RefractiveIndexMaterial

# Tabulated nk material
SiO = RefractiveIndexMaterial(shelf='main', book='SiO', page='Hass')

SiO.get_refractive_index(600)
# 1.96553846

SiO.get_extinction_coefficient(600)
# 0.001

SiO.get_epsilon(600)
# (3.8633404437869827+0.003931076923076923j)

# Formula-based material
bk7 = RefractiveIndexMaterial(shelf='specs', book='SCHOTT-optical', page='N-BK7')
bk7.get_refractive_index(589.3)
# 1.5168...

# Array input
wavelengths = np.array([400, 500, 600, 700])
SiO.get_refractive_index(wavelengths)
# array([2.15092857, 1.999, 1.96553846, 1.942])

Units

All methods accept an optional unit= parameter. Default is nm. The following calls are all equivalent:

bk7.get_refractive_index(589.3)                 # nm (default)
bk7.get_refractive_index(5893, unit='A')         # Angstrom
bk7.get_refractive_index(5.893e-7, unit='m')     # meters
bk7.get_refractive_index(0.5893, unit='um')      # µm
bk7.get_refractive_index(16978, unit='cm-1')     # wavenumbers
bk7.get_refractive_index(508.8, unit='THz')      # terahertz
bk7.get_refractive_index(2.108, unit='eV')       # electron volts

The same parameter works for get_extinction_coefficient, get_epsilon, and get_wl_range.

Here $c$ is the speed of light, $h$ is the Plank constant, $e$ is the elementary charge.

Valid wavelength range

Every material exposes the wavelength range over which its data are defined:

# Returns (min, max) in the requested unit
bk7.get_wl_range()            # e.g. (300.0, 2500.0)   nm
bk7.get_wl_range(unit='um')   # e.g. (0.3, 2.5)        µm
bk7.get_wl_range(unit='cm-1') # e.g. (4000.0, 33333.3) cm⁻¹

Result is always returned as (min, max).

Out-of-range behavior

No exception is raised for out-of-range wavelengths, but the returned value is not reliable:

Always check get_wl_range() before querying if you are not certain the wavelength is within the measured range:

lo, hi = mat.get_wl_range()
if lo <= wavelength <= hi:
    n = mat.get_refractive_index(wavelength)
else:
    raise ValueError(f"wavelength {wavelength} nm is outside the valid range [{lo}, {hi}] nm")

Notes:

• Here the time dependence is assumed to be $\mathrm{e}^{-\mathrm{i} \omega t}$, so $\mathrm{Im}(\varepsilon) > 0$ is responsible for the losses. For the opposite convention, use exp_type:

  SiO.get_epsilon(600, exp_type="exp(+iwt)")  # (n - ik)^2
  # (3.8633404437869827-0.003931076923076923j)
  

  The default is exp_type="exp(-iwt)". You can also write "exp(iwt)", j instead of i, and ω instead of w, for example "exp(-jωt)". Here j is the imaginary unit, so only the sign selects the convention. The old names "exp_minus_i_omega_t" and "exp_plus_i_omega_t" also work.
• If there is a space in the name, write underscore instead, i.e. not page='Rodriguez-de Marcos' but page='Rodriguez-de_Marcos'.
• All 9 dispersion formula types used by the refractiveindex.info database are supported: Sellmeier (1), Sellmeier-2 (2), Polynomial (3), RefractiveIndex.INFO (4), Cauchy (5), Gases (6), Herzberger (7), Retro (8), and Exotic (9).
• The database is automatically downloaded on first use to ~/.refractiveindex.info-database.

How to get material page names

You can find the proper "page" name by hovering your cursor on the link in the Data section

Or you can look up folders in this repository
https://github.com/polyanskiy/refractiveindex.info-database

Similar projects

• PyTMM by Pavel Dmitriev — the original database parsing code this project was based on
• RefractiveIndex.jl — Julia interface to refractiveindex.info database

Possible problems

If the upstream database has changed its structure, upgrade the package

pip install --upgrade refractiveindex

and remove the database folder at ~/.refractiveindex.info-database.

TODO

1. Include EODG data