Seminars & Colloquia Calendar

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Mathematical Physics Seminar

The caustic of colours in Newton’s prism

Michael Berry – University of Bristol, Europe

Location:  Zoom
Date & time: Wednesday, 21 December 2022 at 10:45AM - 11:45PM

Abstract: A single ray of white light, incident on a glass prism, emerges as a family of diverging rays. These originate not from a point focus but from a virtual caustic (envelope of the coloured rays): a tiny structure hidden inside Newton’s prism. The ‘caustic of colours’ is a different singularity from the familiar coloured caustics such as rainbows. Dispersion is typically weak, leading to analytical approximations that completely describe the virtual caustic and enable rendering to simulate its visual colours. The caustic region is very small; observing it with a beam narrow enough to resolve its colours without spreading would require a prism many metres in size. Observability depends on the third power of dispersion, so the caustic, though not its colours, might be detectable by extension outside the visual range, for example in water.

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