Interferometric hologram evaluation and real-time vibration analysis of diffuse objects

Heterodyne Holographic Interferometry

Two-reference-beam holographic interferometry

Since its invention in 1965, holographic interferometry has found many applications, mainly in deformation and vibration analysis of solid objects, but also in the investigation of transparent objects with refractive-index changes and in holographic contouring. In numerous works, all kind of methods for the observation and interpretation of the interference fringe pattern have been elaborated. However, in spite of many propositions for quantitative evaluation of holographic interferograms, the major applications of holographic interferometry in industry are still based on qualitative interpretation of the interferograms. The historical reasons are: insufficient accuracy and density of data obtained from interference fringe counting, lack of automated fringe evaluation methods which avoid time consuming manual evaluation, and furthermore quantitative methods often required complicated optical arrangements to simplify the calculation and interpretation.

Two-Reference-Beam Holographic Interferometry

Publisher Summary Interferometry is an old and very powerful technique to measure the deviation between two wavefields with a sensitivity of a fraction of a wavelength. In holographic interferometry, at least one of the wavefields to be compared interferometrically is stored in a hologram. The hologram is usually recorded experimentally with the help of a reference wave. However, computer-generated holograms constructed theoretically may also be used to supply special, previously not existing wavefields. In most cases, the hologram itself also acts as the beamsplitter for the superposition of the two wavefields. Holographic interferometry has some unique properties, which makes it superior to classical interferometry; wavefields from the same object, but under different conditions and at different times, can be compared. This is an essential prerequisite to compare interferometrically different states of solid objects with opaque, diffusely scattering surfaces. Transient wavefields can be frozen instantaneously by short exposure times. Time averaged wavefields can be recorded and compared afterward. This results in reduction of noise and increase of accuracy and stability.

I Heterodyne Holographic Interferometry

Holograms recorded with a number of reference beams are sensitive to alignment when reconstructed Interference effects due to misalignment are evaluated, and as a result optimal recording parameters can be suggested

Some characteristics of multibeam holography

Using circularly polarized light, high‐quality holograms can be obtained, containing information on the polarization characteristics of the object. A theoretical derivation and some experimental demonstrations are given.

Improved polarization holography

Holography with 1-mW Laser

Triple exposure holographic interferometry provides knowledge of the displacement vector. Between the first two exposures the object is displaced by a calibrated amount, and before the last exposure it is translated by an unknown amount.

Measuring the displacement vector by holographic interferometry

The quality of the first-order diffracted laser beam that emerges from an acousto-optic light modulator has been studied, while changing the diameter and the convergence of the incident beam.

J. Politch

Papers

Some characteristics of multibeam holography

Improved polarization holography

Holography with 1-mW Laser

Measuring the displacement vector by holographic interferometry

Analyzing the quality of the first order diffracted laser beam emerging from an acousto-optic modulator