Holographic interferometry.
Since its inception three decades ago, holographic interferometry has proven to be a powerful nondestructive testing technique for the measurement of displacement and its derivatives. It is a whole-field, noncontact method which requires the use of a hologram to record three-dimensional information about the surface of an object. After a stress is applied to the object, its new surface geometry is compared with the previously recorded state. Changes of the surface of the object, which are manifest as a series of interference fringes superimposed on the image of the object, can be observed statically or in real time to reveal the displacement. Current state-of-the-art techniques such as heterodyne and digital phase shifting interferometry, which have extended the resolution of holographic interferometry far beyond fringe counting, are reviewed. Particular emphasis is placed upon applications in biomedical engineering and medicine, although potentially applicable techniques from other disciplines are examined. The paper is broken into two main parts. In the first part, the scope and potential limitations of this branch of metrology are presented. In the second part, a review of applications in biomedical engineering is presented. The references cited in the first section are the seminal papers in the field. The applications section, which relies upon the results of the first section, presents a critical review of the literature by analyzing the results of a few representative studies.