Compensation-friendly two-wavelength contouring method in holographic interferometry

Abstract

The development efforts in two-wavelength contouring methods of holographic interferometry are mainly along one line: The lateral shift between two images that are recorded at two different wavelengths but are both reconstructed at one of them is to be eliminated as automatically as possible. The present paper takes an opposite approach. A manual elimination process is intentionally maintained, and it is supported by precise visual monitoring. The advantage of this approach is threefold. First, the final accuracy of the elimination is visually displayed and controlled with interferometric precision. Second, exaggerated tilt compensation can result in the subtraction of an extra compensation fringe system from the real one to be measured. In this way, object positioning inaccuracies can be compensated and in addition the upper limit of the measuring range can be extended. In our experiments, a threefold measuring range extension was demonstrated. Third, the intensities of the two reconstructed images can be adjusted to each other if needed. Tilt compensation and intensity adjustment are especially advantageous features at the realization of the comparative two-wavelength contouring by difference holographic interferometry.