Heterodyne holographic interferometry
Abstract
The sources of error of a heterodyne holographic interferometer for the determination of displacement and mechanical strain of an arbitrarily shaped object were investigated. Laser properties, rotating grating, interferometer, coherent imaging, photodetection and electronic phase measurement are discussed. The importance of a sufficient signal to noise ratio and signal level of the modulated detector output is shown. The accuracy of the phase measurements is limited by phase fluctuations due to refraction index fluctuations and mechanical drift. An automated system which measures phase differences between two neighboring points on the object is described. It is shown that the displacement and strain components can be measured using one hologram and three or five points of observation, with an accuracy of 10 nm and 1 microstrain. Interferometers with heterodyne phase detection are discussed.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- December 1981
- Bibcode:
- 1981STIN...8333120B
- Keywords:
-
- Holographic Interferometry;
- Imaging Techniques;
- Optical Heterodyning;
- Error Analysis;
- Gratings (Spectra);
- Phase Detectors;
- Phase Error;
- Photometers;
- Signal To Noise Ratios;
- Instrumentation and Photography