ESPI—The ultimate holographic tool for vibration analysis?

Abstract

Electronic speckle pattern interferometry—ESPI—may be described as image holography, where the TV-target has replaced the the photographic film as recording medium while the optical reconstruction is simulated by videoprocessing and display. ESPI can do similar interferometric measurements as holography, but the technique is especially suitable for measurements on vibrating objects. Here the object's vibration mode is displayed as easily interpretable fringe patterns across the monitor image without time delay and at a high repetition rate. ESPI permits measurements on difficult, unstable objects in adverse environments. Using optical phase-modulation techniques in ESPI, we obtain an extended measuring range (lower-upper limits 0.01–10 000 NM), separate contours of constant amplitude and phase, dynamic display of the vibration cycle and direct comparison between vibrating objects. The ESPI technique has been applied in various industrial and biomedical projects, which will be described. The general properties outlined above together with some samples of vibrating objects will be illustrated by a short movie.