A Technique for Obtaining Improved Real-time Holographic Interferometric Data Using Pulse Modulated Illumination

Book excerpt: Calculations and experiments were performed to show that the fringe patterns on a vibrating structure, as observed using real-time holographic interferometry, has a substantially increased contrast ratio if the laser illumination is amplitude modulated by a sequence of pulses which are synchronized with the vibration. The time and effort required to obtain interferometric data using this method is an order of magnitude less than that needed when using time-average holographic interferograms. Potential applications include experimental studies of fatigue damage, crack detection and propagation, flaw detection in composite and honeycomb structures as well as vibration analysis of structural members.