environment.air_index#

Unified Interface for Air Refractive Index Models.

This module provides a high-level dispatcher function, refractive_index_air, to conveniently access various models for calculating the refractive index of air. This allows users to easily switch between models based on their specific requirements for accuracy, environmental conditions, or consistency with other tools.

The supported models include:

  • Ciddor (1996): A highly accurate model for a wide range of wavelengths and atmospheric conditions.

  • Edlén (1966): A widely used model, implemented here with the NIST temperature correction for the water vapor term to improve accuracy.

  • Birch & Downs (1994): A revised Edlén-style equation, also implemented with the NIST temperature correction for the water vapor term.

  • Kohlrausch: A model based on the formula used in Zemax OpticStudio.

Kramer Harrison, 2025

Functions

refractive_index_air(wavelength_um, conditions)

Calculates the refractive index of air using a specified model.
refractive_index_air(wavelength_um: float, conditions: EnvironmentalConditions, model: str = 'ciddor') → float[source]#

Calculates the refractive index of air using a specified model.

This function acts as a dispatcher to various air refractive index models. The environmental conditions (temperature, pressure, humidity, CO2) are encapsulated in the conditions object.

Parameters:

  • wavelength_um – The wavelength of light in a vacuum, in micrometers (μm).

  • conditions – An EnvironmentalConditions object containing the environmental parameters (temperature, pressure, humidity, CO2).

  • model – The model to use for the calculation. Supported models are: ‘ciddor’, ‘edlen’, ‘birch_downs’, ‘kohlrausch’. This is case-insensitive. Defaults to ‘ciddor’.

Returns:

The calculated refractive index of air.

Raises:

  • ValueError – If an unsupported model is specified.

  • TypeError – If conditions is not an EnvironmentalConditions object.

Example

>>> from optiland.environment import EnvironmentalConditions
>>> conditions_std = EnvironmentalConditions(
...     temperature=15.0,
...     pressure=101325.0,
...     relative_humidity=0.0,
...     co2_ppm=400.0,
... )
>>> n_ciddor = refractive_index_air(0.55, conditions_std, model="ciddor")
>>> print(f"Refractive index at 0.55 µm is {n_ciddor:.8f}")
Refractive index at 0.55 µm is 1.00027764