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.. |doi| image:: https://zenodo.org/badge/DOI/10.5281/zenodo.8370821.svg :target: https://doi.org/10.5281/zenodo.8370821 :alt: doi

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.. |test| image:: https://github.com/scottprahl/pygrin/actions/workflows/test.yaml/badge.svg :target: https://github.com/scottprahl/pygrin/actions/workflows/test.yaml :alt: Testing

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.. |downloads| image:: https://img.shields.io/pypi/dm/pygrin?color=68CA66 :target: https://pypi.org/project/pygrin/ :alt: Downloads

.. |lite| image:: https://img.shields.io/badge/try-JupyterLite-68CA66.svg :target: https://scottprahl.github.io/pyspeckle/ :alt: Try Online

pygrin

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

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.. image:: https://raw.githubusercontent.com/scottprahl/pygrin/main/docs/pitch.png :alt: full pitch lens

Example

Properties of 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

Use pip::

pip install pygrin

or conda::

conda install -c conda-forge pygrin

or use immediately in your browser via the JupyterLite button below

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Citation

If you use pygrin in academic or technical work, please cite:

Prahl, S. (2026). pygrin: A Python module for ray tracing through gradient-index (GRIN) lenses (Version 0.6.1) [Computer software]. Zenodo. https://doi.org/10.5281/zenodo.8370821

BibTeX

.. code-block:: bibtex

   @software{pygrin_prahl_2026,
     author    = {Scott Prahl},
     title     = {pygrin: A Python module for ray tracing through gradient-index (GRIN) lenses},
     year      = {2026},
     version   = {0.6.1},
     doi       = {10.5281/zenodo.8370821},
     url       = {https://github.com/scottprahl/pygrin},
     publisher = {Zenodo}
   }

License
-------
``pygrin`` is licensed under the terms of the MIT license.