In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
Thy Godlike crime was to be kind,
To render with thy precepts less
The sum of human wretchedness,
And strengthen Man with his own mind;
But baffled as thou wert from high,
Still in thy patient energy,
In the endurance, and repulse
Of thine impenetrable Spirit,
Which Earth and Heaven could not convulse,
A mighty lesson we inherit.
Like thee, Man is in part divine,
A troubled stream from a pure source;
And Man in portions can foresee
His own funereal destiny;
His wretchedness, and his resistance,
And his sad unallied existence:
To which his Spirit may oppose
Itself—and equal to all woes,
And a firm will, and a deep sense,
Which even in torture can descry
Its own concenter'd recompense,
Triumphant where it dares defy,
And making Death a Victory.