# pygrin¶

A basic collection of routines to ray trace through graded index (GRIN) lenses with a parabolic radial profile.

## Usage¶

Example Light paths in a 0.25 pitch GRIN lens from an ancient Melles Griot Catalog:

```
import pygrin
n = 1.608
gradient = 0.339
length = 5.37
diameter = 1.8
pitch = pygrin.period(gradient, length)
ffl = pygrin.FFL(n,pitch,length)
efl = pygrin.EFL(n,pitch,length)
na = pygrin.NA(n,pitch,length,diameter)
angle = pygrin.max_angle(n,pitch,length,diameter)
print('expected pitch = 0.29, calculated %.2f' % pitch)
print('expected FFL = 0.46 mm, calculated %.2f' % ffl)
print('expected NA = 0.46, calculated %.2f' % na)
print('expected full accept angle = 55°, calculated %.0f°' % (2*angle*180/np.pi))
print('working distance = %.2f mm'%(efl-ffl))
```

Produces:

```
expected pitch = 0.29, calculated 0.29
expected FFL = 0.46, calculated 0.47
expected NA = 0.46, calculated 0.46
expected full accept angle = 55°, calculated 55°
working distance = 1.43 mm
```

But the real utility of this module is creating plots that show the path of rays through a GRIN lens. For examples, see <https://pygrin.readthedocs.io>

## Installation¶

Source code is available at <https://github.com/scottprahl/pygrin> or the module can be installed using pip:

```
pip install --user pygrin
```