The grating projection system: a laser light pattern projection technique for long distance illumination based on the Talbot effect

Abstract

Inspired by the Talbot effect, a grating projection system was designed. Periodic patterns were produced from a projection of a diffraction grating illuminated by a spherical wave of monochromatic coherent light. The diffracted light was collimated by a lens, the focal distance of which was at the centre of the incident spherical wave. Experiments demonstrated that the diffracted orders were also spherical waves centred on the same transverse plane as the incident light. The periodic illumination observed at different locations along the optic axis was proven to be the result of interference between the diffracted orders. It was demonstrated that this system could be used to measure velocities up to 20 m s−1 of particles crossing the fringes at distances up to 3 m.

Analysis of array illumination generalized by the combination of a binary phase grating and a lens

“…Usually a phase grating is used for Talbot array illuminator because a phase grating has high diffraction efficiency. Though it is not necessary to need a lens to generate array illumination, sometimes a lens is used in industry measurement because a lens has a convergent effect 15 ,which is very important when the light is too weak to be measured. Omitting the definite size of a lens, a lens is considered as a phase element.…”