Vibration Analysis by Double Pulsed Laser Holography

The use of a giant pulse laser with 30 ns double pulses makes it possible to holograph different phases of an object vibration within time intervalls from 100 μs to 1 ms onto the same plate. The vibration phases into which the first and second laser pulse are fired can be exactly preselected by means of an electronic trigger system. The simultaneous reconstruction of the holograms taken by the first and the second laser pulse generates on the object surface a system of interference fringes which are loci of equal displacement. Adjoining fringes correspond to displacement differences of half a wavelength of the laser's light. In this way, it is possible, for instance, to visualize the vibration pattern of car bodies and drive units excited by the running engine.

The method of measurement and a hologram camera especially constructed for making double pulsed holograms of automobiles are described. Several examples of application are quoted in order to illustrate this technique.