The programme examines the use of holographic interferometry to record minute surface deformations on vibrating objects.
|Module code and title:
|ST291, Images and information
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|Stuart Freake; Keith Hodgkinson
|BBC Open University
|Holograms; Interferometry; Lasers; Speckle
|Keith Hodgkinson displays one of the hologram seen on a previous programme. He induces interference fringes in real time on this hologram by pressing the object. Hodgkinson goes on to explain the reason for these fringes and points out possible practical applications for holographic interferometry. Stuart Freake briefly introduces the next demonstration. Keith Hodgkinson uses holographic apparatus at Loughborough University's Department of Mechanical Engineering to demonstrate how one can pick up and freeze movement in a holographic system. He points out the various components of the apparatus and then produces a hologram of himself playing a viola.The fringes representing the vibrating viola are clearly seen. Stuart Freake briefly points out the fringes and their characteristics. Shots of a hologram of a petrol internal combustion engine. The fringes, representing contours of equal motion, are indicative of the strain set up during engine operation. Commentary by Stuart Freake. Keith Hodgkinson demonstrates a technique, using time averaging, for obtaining holographic interferograms for a relatively simple system such as a loudspeaker. He points out the disadvantages of this technique. Stuart Freake and Keith Hodgkinson go on to explain and demonstrate another- technique for obtaining holographic interferograms for a loudspeaker, this time with a stroboscopic (pulsed ruby laser) set tip. They demonstrate the principles involved in freezing a moving object by playing a strobe light on an electric fan and then go on with the holographic demonstration proper. Stuart Freake goes on to examine the speckle effect. This was once a major problem for holography but can now be used to produce interferograms with ordinary television cameras rather than high resolution film. He demonstrates the effect and explains how it occurs. Keith Hodgkinson demonstrates an audio analogy of the speckle effect to help explain why the effect occurs. The output is displayed on an oscilloscope screen. Stuart Freake relates the audio analogy to what is happening in the lens of the television camera. He then goes on to demonstrate a system based on speckle effect which works in real time using live fringes.
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