Optical Ray Tracer

A 3D optical ray tracer written in Python and NumPy, built as part of Imperial College London's second-year physics computing project. It propagates bundles of rays through sequences of refracting surfaces using a vector form of Snell's law, locates focal points, and quantifies imaging performance through spot diagrams and RMS spot-size analysis against the diffraction limit.

What it does

• Vector refraction. physics.refract implements Snell's law in full vector form on arbitrary surface normals, returning the refracted direction and handling total internal reflection.
• Optical elements. A small class hierarchy (OpticalElement → Sphere → SphericalRefraction, plus Plane/OutputPlane) where each element knows how to intercept and propagate a ray. Spherical surfaces compute their own paraxial focal point.
• Compound lenses. PlanoConvex and ConvexPlano lenses are composed of two refracting surfaces, allowing direct comparison of the two orientations of the same singlet.
• Ray bundles. RayBundle generates concentric rings of parallel rays, propagates them through any element sequence, and produces 3D track plots, focal-plane spot diagrams, and the RMS spot size of the bundle.
• Aberration analysis. The analysis tasks sweep input beam radius and compare the geometric RMS spot size against the diffraction scale λf/2r, locating the beam radius at which spherical aberration overtakes diffraction as the dominant blur. The plano-convex vs convex-plano comparison shows the classic result that orientation alone changes the aberration of an identical lens.

Package structure

raytracer/
├── rays.py        # Ray and RayBundle
├── physics.py     # vector Snell's law refraction
├── elements.py    # OpticalElement, Sphere, SphericalRefraction, Plane, OutputPlane
├── lenses.py      # PlanoConvex and ConvexPlano singlet lenses
└── analysis.py    # analysis tasks: focal points, spot diagrams, aberration sweeps
tests/             # pytest suite, including code-quality checks (pylint, pydocstyle, darglint)

Example

Trace a bundle through a single refracting surface and measure the spot at its focal plane:

from raytracer.rays import RayBundle
from raytracer.elements import SphericalRefraction, OutputPlane

surface = SphericalRefraction(z_0=100, aperture=10, curvature=0.03, n_1=1.0, n_2=1.5)
screen = OutputPlane(surface.focal_point())

bundle = RayBundle(rmax=5.0, nrings=5, multi=6)
bundle.propagate_bundle([surface, screen])

bundle.track_plot()              # 3D ray paths
bundle.spot_plot()               # spot diagram at the focal plane
print(f"RMS spot size: {bundle.rms():.4f} mm")

Running the tests

pip install -e .
pytest

The test suite checks both physical correctness of the tasks and code quality via pylint, pydocstyle and darglint.

Background

Written for Imperial's Year 2 Physics Computing Lab (Project A). The project brief and test scaffolding were provided by the course; all ray-tracing physics, element classes, lens models and analysis are my own implementation.