MULTIPLE-WAVELENGTH HOLOGRAPHIC-INTERFEROMETRY

A number of interesting and useful interferometric measurements can be obtained by using more than one wavelength. The following report disc usses how holography enhances both the possibilities and results obtai ned from multiple-wavelength interferometry. A discussion of approache s is followed by a number of examples from our own laboratory work in this area. In the first example, two widely separated wavelengths are employed to exploit the dispersive properties of a solution to measure temperature and concentration simultaneously. In this case holographi c recording makes phase-shifting interferometry possible with a snapsh ot recording. In the second example, the use of anomalous dispersion a t the resonance of a gas is exploited to measure species concentration . This is accomplished by direct optical subtraction of the two differ ent wavefronts, one at resonance and the other off resonance. Finally, two closely spaced wavelengths are reflected from a diffuse surface a nd subtracted optically by holography to contour a surface.