Real-time monitoring of vibration fringe patterns by optical reconstruction of digital holograms: mode beating detection

A new technique capable of monitoring two- dimensional vibration fringe patterns in real- time is presented. It is based on optical reconstructing of time- averaged digital holograms. Recording of the holograms is realized in a quasi- Fourier off- axis setup whilst reconstructing in an extended Fourier transform setup capable of spatial filtering of the hologram reconstructions. The effectiveness of the proposed device, tested on a silicon wafer, was verified by performing operations such as monitoring of vibration modes, adjusting the hologram recording parameters, or searching for resonant frequencies. Additionally, mode beating between two distant vibration frequencies is observed and reported. The proposed technique is suitable for various scientific and industrial applications. (c) 2006 Optical Society of America.