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Poisson–Arago Spot

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About this simulation

Scalar Fresnel diffraction from an opaque circular disk approximates the sphere’s silhouette. The incident wave is monochromatic and planar. The on-axis intensity equals the unobstructed intensity I₀. Screen brightness uses fixed exposure; refraction and reflection are omitted.

What students can explore

  • Can a shadow have a bright centre? Change the sphere radius, wavelength and screen distance.
  • Light bending around an opaque sphere creates a bright point at the centre of its shadow. Switch to geometric rays to compare.

Learning objectives

  1. 1Can a shadow have a bright centre? Change the sphere radius, wavelength and screen distance.

Questions teachers ask

How does this work?

Scalar Fresnel diffraction from an opaque circular disk approximates the sphere’s silhouette. The incident wave is monochromatic and planar. The on-axis intensity equals the unobstructed intensity I₀. Screen brightness uses fixed exposure; refraction and reflection are omitted.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

<iframe src="https://kiwibee.io/en/simulations/poisson-arago-spot-simulation/embed" title="Poisson–Arago Spot | KiwiBee" loading="lazy" allowfullscreen style="width:100%;height:min(70vh,620px);min-height:420px;border:0;border-radius:16px"></iframe>

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