Refractive index of air, and vacuum-air wave length conversion.

## Project description

Code for calculating refractive index of air, under varying atmospheric conditions, is provided in this module. Functions for conversion of wave length of light in vacuum to that in air, and vice-versa are also defined.

The code is based on the documentation for the NIST online refractive index of air calculator.

## Examples

Refractive index can be calculated using two different equations: one due to Edlén and another due to Ciddor.

```>>> ref_index.ciddor(wave=633.0, t=20, p=101325, rh=20)
1.0002716285340578
>>> ref_index.edlen(wave=633.0, t=20, p=101325, rh=20)
1.0002716291691649
>>> ref_index.edlen(wave=633.0, t=20, p=101325, rh=80)
1.0002711197635226
>>> ref_index.ciddor(wave=633.0, t=20, p=101325, rh=80)
1.0002711183472626
>>> ref_index.edlen(wave=633.0, t=60, p=101325, rh=80)
1.0002339748542823
>>> ref_index.ciddor(wave=633.0, t=60, p=101325, rh=80)
1.0002340241754055
```

Conversion of wave length of light in vacuum to that in air, and vice-versa. Both of these functions use the Ciddor equation, as implemented in ciddor_ri() and ciddor().

```>>> ref_index.vac2air(633.0)
632.82500476826874
>>> ref_index.air2vac(632.82500476826874)
633.00000139949032

>>> ref_index.vac2air(np.array([633.0, 550.0, 400.0]))
array([ 632.82500477,  549.84723175,  399.88692724])
>>> x = ref_index.vac2air(np.array([633.0, 550.0, 400.0]))
>>> ref_index.air2vac(x)
array([ 633.0000014 ,  550.00000164,  400.00000243])
```

Note that the reversibility of air2vac() is ~1e-5nm.

Default temperature is 15∘C, pressure is 101325Pa, relative humidity is 0, and CO2 concentration is 450µmole/mole. All these can be changed.

```>>> ref_index.vac2air(633.0, t=20, p=100000.0, rh=50)
632.83051710791892
>>> ref_index.air2vac(632.83051710791892, t=20, p=100000.0, rh=50)
633.00000131884678
```

For more details please see the docstring for the module. Detailed description of the equations can be found in the NIST documentation.

## Installation

The module can be installed using pip and easy_install.

```\$ pip install ref_index
```

or,

```\$ easy_install ref_index
```

## Credits

All equations used in this module come from the documentation for the NIST online refractive index calculator, written by Jack A. Stone and Jay H. Zimmerman.

Please send comments and suggestions to the email id prasanthhn in the gmail.com domain.

## Project details 