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

Basics of Holography is a general introduction to the subject written by a leading worker in the field It begins with the theory of holographic imaging, the characteristics of the reconstructed image, and the various types of holograms Practical aspects of holography are then described, including light sources, the characteristics of recording media and recording materials, as well as methods for producing different types of holograms and computer-generated holograms Finally, important applications of holography are discussed, such as high-resolution imaging, holographic optical elements, information processing, and holographic interferometry The book includes comprehensive reference sections and appendices summarizing some useful mathematical results Numerical problems with their solutions are provided at the ends of chapters This is an invaluable resource for advanced undergraduate and graduate students as well as researchers in science and engineering who would like to learn more about holography and its applications in science and industry

Basics of Holography

Holographic interferometry is a very powerful technique for the measurement of small deformations and displacements of opaque solid objects. Unfortunately, the quantitative interpretation of the fringe patterns is somewhat involved, and the large number of papers published on this subject in the past 10 years has caused considerable confusion. This review paper is an attempt to rationalize the field by classifying the many different interpretation schemes into four main techniques, and by offering guidelines for the choice of technique for different applications.

The interpretation of holographic interferograms

Holographic, speckle and moiré techniques in optical metrology

Examples of industrial holographic measurements. Some of the holograms were exposed in workshop environment. Holograms were made of detached machine parts that, between exposure and real-time observation, were taken out of the holographic rig and used in the machine.

Industrial Holographic Measurements

A method of evaluating time-average holograms which gives the vibration amplitudes of an object is described. The method is based on the holodiagram, from which a value of sensitivity ( k value) is obtained. For sinusoidal vibrations of an object, a k values are calculated from the roots of the zero order Bessel function; these give the values of the vibration amplitude at the dark interface fringes directly by multiplication with the wave-lenght of the laser light and appropriate k value. a k values are tabulated for the first twenty fringes. a He values which incorporate the wavelenght of the commonly used He-Ne laser are also tabulated. The evaluation of a hologram of a metal sheet is described. Finally the difference between the position of fringes obtained from objects with sinusoidal and square-wave amplitudes of vibration is shown.

Simplified interpretation of interference fringes obtained by time-average holography

A structure dynamic model of an airplane fin built by Saab-Scania, Sweden, has been vibration tested by the holographic time-average technique. The investigation was performed at Volvo-Flygmotor, Sweden, in their vibration laboratory. Holograms were made at every resonance frequency and, in all, eleven different patterns were created in the interval from 0 to 3 400 Hz. The inner structure of the fin model was revealed by inducing a temperature difference between the two exposures of a double-exposed hologram.

H. Bjelkhagen

Papers

Simplified interpretation of interference fringes obtained by time-average holography

Holographic time-average vibration study of a structure dynamic model of an airplane fin