Speckle Pattern Interferometry of Vibration Modes

An optical facility is described for the study of the vibrational behavior of engineering test pieces. Time-average holography
and electronic speckle pattern methods of analysis are combined into one system. The speckle pattern method is used for the identification
of resonances, frequency tuning, and object alignment, thereby optimizing the number of holographic exposures. An evaluation is
made of the electronic speckle pattern method for the detection of vibration modes of three-dimensional objects. The method is shown
to detect resonant vibration readily on object faces inclined at angles up to 60° to the viewing direction.