An appraisal and developments of laser holography for interferometric engineering measurement

Holography is a two-stage method of imagery in which both amplitude and phase information characterizing a wavefront are recorded, and subsequently reconstructed. Only with the advent of laser light sources in the early 1960s did the method become practical, motivating research into applications. One of these, holographic interferometry, was based on the fact that a reconstructed wavefront from a hologram could be used as a reference for interferometric comparison. This enabled interferometry to be extended to objects having scattering surfaces of any shape, and the potential of the method in engineering measurement was considered to be high. A literature survey carried out at the start of this project (1967 to 1968), and reported in Chapter 2, revealed that many potential applications in the fields of stress analysis, vibration analysis, fault detection in materials and structures, and dimensional inspection, had been proposed but were not quickly materializing. This was seen to be partly due to practical difficulties necessitating laboratory procedures, and partly due to difficulties in analysing interferograms to obtain specific measurements. Accordingly, the aims of this project were: (i) to develop apparatus and methods that would simplify and improve the practice of holographic interferometry and the interpretation of results; (ii) to investigate fringe interpretation, and to assess the accuracy and general feasibility, in relation to practical measurements of surface deformation. [Continues.]