Sandwich holography - An analogue method for the evaluation of holographic fringes
Abstract
Sandwich-hologram interferometry represents some of the advantages of real-time hologram interferometry but without the need of interferometric precision during reconstruction. A series of holographic plates can be exposed during a stepwise loading of the object. In the reconstruction stage, any two holograms can be compared interferometrically simply by being sandwiched together, e.g., with their emulsions outwards. A tilt of the sandwich hologram during reconstruction will introduce shearing fringes on the holographic image that are either added to or subtracted from fringes caused by object tilt. Evaluation of object tilt can be made by measuring the analogous but much larger sandwich tilt needed to eliminate the fringes on the reconstructed object. The sandwich hologram makes possible the elimination of spurious fringes as well as the evaluation of the sign of displacement and of the maximal object stress and strain. When sandwich holography is used for contouring purposes, the interference planes intersecting the object can be tilted during reconstruction more than 90 deg in any direction.
- Publication:
-
The Engineering Uses of Coherent Optics
- Pub Date:
- 1976
- Bibcode:
- 1976euco.proc..631A
- Keywords:
-
- Diffraction Patterns;
- Holographic Interferometry;
- Photographic Plates;
- Wave Front Reconstruction;
- Holography;
- Instrument Errors;
- Optical Correction Procedure;
- Performance Tests;
- Photographic Emulsions;
- Real Time Operation;
- Sandwich Structures;
- Technology Utilization;
- Instrumentation and Photography