Historically, the concept of replacing the photographic emulsion by video recording and display occured to several independent groups almost simultanously. Macovsky(1) in USA, Schwomma(2) in Austria and Kopf(3) in West-Germany considered the technique to be based on pure holography. The Lougborough group in England, headed by Butters and Leendertz(4) viewed the technique more as an off-spring of their speckle work and they also introduced the name ESPI as an abbreviation for electronic speckle pattern interferometry. Although the ESPI-name might be considered appropriately descriptive, its association with coarse, annoying speckles has undoubtedly hampered the general acceptance of the technique. Video holography might be a name with better sales appeal, but might be confused with techniques for direct transmission of three-dimensional holographic images(5).

http://iopscience.iop.org/article/10.1088/0305-4624/11/1/303/pdf

Electronic speckle pattern interferometry

In this paper we describe a double-pulsed electronic speckle interferometry system. Two separated speckle patterns are recorded within few microseconds using a charge-coupled device camera, the two images are then stored in a frame grabber and the subtraction method is applied. A quantitative analysis of the fringes using the spatial-carrier phase-shift method is presented. The results show that this method is well suited to study transient vibrations.

/pdf/double-pulse-electronic-speckle-interferometry-23nll0lpkl.pdf

Double pulse-electronic speckle interferometry

We describe a double-pulse electronic-speckle-interferometry system. Two separate speckle patterns of an object being tested are recorded within a few microseconds with a CCD camera. Their two images are stored in a frame grabber. The fringes obtained from subtraction are quantitatively analyzed by the spatial-carrier phase-shift method. Using three directions of illumination and one direction of observation, one can record at the same time all the information necessary for the reconstruction of the three-dimensional deformation vector. Applications of this system for measuring the rotating objects are discussed for the case for which a derotator needs to be used. Experimental results are presented.

/pdf/double-pulse-electronic-speckle-interferometry-for-vibration-2tgn33zdkl.pdf

Double-pulse electronic speckle interferometry for vibration analysis.

The use of digital image processing techniques for electronic speckle pattern interferometry is discussed. A digital TV-image processing system with a large frame memory allows us to perform precise and flexible operations such as subtraction, summation, and level slicing. Digital image processing techniques make it easy compared with analog techniques to generate high contrast fringes. Some experimental verifications are presented in the cases of surface displacement and vibration amplitude measurements.

Electronic speckle pattern interferometry using digital image processing techniques.

An application of digital image processing techniques to speckle-shearing interferometry is described. A present system consists of an image-shearing camera using a Fresnel biprism of small angles and a digital TV-image processing facility. This interferometer makes it easy to measure in quasi-real-time spatial derivatives of surface displacement and modal vibration amplitude of objects. A statistical theory is applied to analyze the formations of these fringes due to 3-D displacement. Interpretation of the result leads to conditions of maximum fringe contrast and the limitation of this technique. Experimental results in the three cases of slope of normal displacement, surface strain, and slope of vibration amplitude measurements are presented.

Digital speckle-pattern shearing interferometry.

This paper describes the incorporation of a pulsed ruby laser into an electronic speckle pattern interferometer. A technique is described for observing vibrational and transient events with a double pulsed laser and some typical results are given. Results of the application of the interferometer to non-destructive testing are included.

H.C. Pollard

Papers

Pulsed lasers in electronic speckle pattern interferometry