Following the path of light: recovering and manipulating the information about an object

Abstract

The light diffused by an illuminated object contains information about it but, as it propagates, the information changes its appearance and sometimes seems even lost. The more conventional way to retrieve this information is to make an image of the object by means of some optical device, like a lens or a mirror. Nevertheless this is not the only way to proceed: pin-hole photography, for instance, recovers some part of the information by simply selecting a single light ray from each point of the object, on the other hand, holography recovers the largest part of information about the object by registering an interference pattern. Moreover, propagating light can be manipulated in such a way that the final recovered information results dramatically different from the original one. The only way not to get confused in the description of all these phenomena in the didactic practice with High-School students is to follow the path of light asking how the information is present during the propagation of the light. We tested this approach experimentally by realizing 2D images with pin-hole cameras and photo-cameras and 3D images with a holographic setup and implementing spatial filtering in the focal plane of a lens: the result was a deeper understanding by students.