Broadband photorefractive interferometer system for full field imaging of periodic and transient displacement fields

Photorefractive interferometry (PRI) offers a number of important intrinsic advantages over conventional interferometry techniques. The focus of this work lies on the exploitation and extension of the concept of \textquotedblleft two-wave mixing \textquotedblright \ PRI for the spectrally resolved detecting/imaging of mixed acoustic vibrations, and for the visualization of transient surface acoustic wave (SAW) propagation.In order to gain a better insight of the photorefractive effect and its advantages and limitations in vibrometry applications, a theoretical basis is given on the two-wave mixing process in photorefractive materials, and implemented for 2 new photorefractive interferometry approaches proposed in this work.The first proposed approach allows to selectively detect weak periodical vibrations, with minimum cross-talk from large vibrations. The method was extended for spectrally resolved imaging of one frequency component from a mixing-frequency vibration pattern, thus offering a rapid alternative for nonlinear acoustics nondestructive testing (NDT) based on scanning laser vibrometry. A stroboscopic imaging technique based on photorefractive interferometry is proposed for the visualization of SAW propagation with nanosecond time resolution by simple us of a standard charge-coupled device (CCD) camera.

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