Illumination Edge Research Articles

Effect and applications of patterned laser illumination on superconducting films

Patterned laser illumination incident upon superconducting films is shown to be capable of creating dynamic superconducting-normal ($S\ensuremath{-}N$) interfaces with almost any desired pattern. The width of such a dynamic interface for a sharp illumination edge is shown to be the effective quasiparticle diffusion length. In the limit of strong phonon trapping in the film, the effective quasiparticle diffusion length approaches the thermal healing length obtained from the heat diffusion model. However, this is not the appropriate limit in general for thin films immersed in liquid helium. The ability to create dynamic $S\ensuremath{-}N$ patterns can be used in probing spatial inhomogeneity of superconducting films and tunnel junctions. An Al-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$-Pb junction was used to demonstrate the technique. For the first time, the spatial distribution of tunneling probability was obtained through the measurements of local Josephson current. It is shown that this is a much more reliable technique than attempting to infer the tunneling probability from the excess quasiparticle tunneling current due to a local laser or electron beam excitation.

Recognition of reflection and illumination edges by the human visual system

A simple two-stage lateral-inhibition mechanism is described that permits edges due to changes in surface illumination and orientation to be distinguished directly in the retina from those due to changes in spectral reflectivity. It is based on the assumption that the spectral content of the reflected light changes acrpss a reflectivity edge, whereas it remains relatively constat across an illumination edge.

The detectability of an unsharp edge in an additive noisy background.

The detectability of one part of an illuminated field which has a straight edge as the border to the remaining part of the field was studied experimentally while the illumination of the total field had an irregular contrast based on a gaussian-noise spatial structure. The two parts of the field had different average illuminations. The detectability of the edge was studied for various illumination differences, field areas, edge lengths, and sharpnesses. The results are discussed in terms of the characteristics of the background noise and the visual system. The observations are interpreted in terms of a model that assumes spatial differentiation and spatial integration.