The Role of Retro-Reflective Materials in Holography

Abstract

In taking holograms of solid components, laser light i reflected from the surface of the component to the hologram. In general, the surfaces involved are diffuse, which scatter the reflected light cau ing large intensity los es of the incident illumination and also a depolarization of the highly polarized incident laser light. To illuminate large diffu e surfaced components requires large expensive lasers. The authors have used mall inexpensive la er and retro-reflective coatings on large components, enabling all the incident low intensity laser illumination to be reflected to the hologram. The polarization of the laser light remain unaffected after reflection at the component surface. By retaining the polarization of the incident illumination, high contrast real time fringes are obtained in hologram interferometers. The authors di Cll s the history of retro-reflection referring to British and US Patents and have reviewed the uses of such materials in holography. The main constituent of the latest retro-reflective paints and tapes is an extremely small phere having a core of very high refractive index glass, the outer surface of the sphere being chemically treated to give a lower refractive index: orne retro-reflecli e tape use conventional glass spheres. Such small spheres have been used as imaging lenses with both monochromatic and non-monochromatic component illumination to create 3D images, the images being comparable to those obtained by lenticular or fly’s-eye creen techniques.