Visualization of patterns corresponding to the Fourier components of a vibration by interference holography

Two techniques were applied to visualize patterns of an object in harmonic vibration. The compensation technique for unwanted rigid body motions can be used with time-average holography, where a very narrow reference bream is led to the hologram via the object under investigation. It is possible to take time-average holograms of objects vibrating with a variable amplitude, which is impossible otherwise. The second technique is double-pulse holography. The high demands on the rigidity of the setup can then be diminished and also vibrations with more than one direction of motion and variable amplitude can be studied. To obtain reproducible results a synchronization between the mechanical vibration and the laser system is realized. It is possible to fire the light pulses in a predetermined phase of the vibration and to visualize on a metal plate the vibration pattern corresponding to one of the Fourier components from a complex vibration.